tren - Advanced File Renaming


tren is a powerful command line file/directory renaming tool. It implements a variety of sophisticated renaming features than can be a bit complex to learn. For this reason, this document is split into two general sections: "REFERENCE" and "TUTORIAL AND DESCRIPTION". If you are new to tren, start by studying the latter section first. It will take you from very simple- to highly complex tren renaming operations. Once you've got a sense of what tren can do, the reference section will be handy to look up options and their arguments.


tren is very powerful and can easily and automatically rename things in ways you didn't intend. It is strongly recommended that you try out new tren operations with the -t option on the command line. This turns on the "test mode" and will show you what the program would do without actually doing it. It goes without saying that you should be even more careful when using this program as the system root or administrator. It's quite easy to accidentally rename system files and thereby clobber your OS. You have been warned!!!


SYNOPSIS [-aCcdfhqtvXx] [-A alphabet] [-I file] [-i range]  [-P esc] \
        [-R sep] [-r old=new] [-S suffix] [-w width]     file|dir ...


You may specify tren options in one of three ways:

  1. On the command line
  2. In an "include" file specified with -I filename on the command line
  3. Via the $TREN environment variable

Options specified on the command line are evaluated from left to right and supercede any options specified in the environment variable. Think of any options set in $TREN as the "leftmost command line options".

All options must precede the list of files and/or directories being renamed. If one of your rename targets start with the - character, most command shells recognize the double dash as an explicit "end of options" delimiter: -opt -opt -- -this_file_starts_with_a_dash

The list of items targeted for renaming must name directories or files that exist or be a wildcard that expands to existing directories or files. If you specify a non-existent renaming target, tren will display an error and stop further processing.

Most shells aren't too fussy about space between an option that takes an argument, and that argument:

-i 1

Use whichever form you prefer. Just be aware that there are places where spaces matter. For example, you can quote spaces on your command line to create renaming requests that, say, replace spaces with dashes..

Some options below are "global" - they change the state of the entire program permanently and cannot be undone by subsequent options. Some options are "toggles", they can be turned on- and off as you move from left- to right on the command line. In this way, certain options (like case sensitivity, regular expression handling, and so on) can be set differently for each individual renaming request (-r). (If you're very brave, you can select the -d option to do a debug dump. Among many other things, the tren debugger dumps the state of each renaming request, and what options are in effect for that request.)


-A alphabet

Install a user-defined "alphabet" to be used by sequence renaming tokens.

(Default: Built-in alphabets only)

The alphabet is specified in the form:


Both the name and the characterset are case- and whitespace-sensitive (if your shell permits passing spaces on the command line). The "0th" element of the alphabet is the leftmost character. The counting base is the length of characterset. So, for instance, the following alphabet is named Foo, counts in base 5 in the sequence, a, b, c, d, e, ba, bb, ...:

-A Foo:abcde

Ask interactively before renaming each selected file or directory.

(Default: off)

If you invoke this option, tren will prompt you before renaming each file. The default (if you just hit Enter) is to not rename the file. Otherwise, you have the following options:

n - Don't rename the current file

y - Rename the current file

! - Rename all the remaining files
    without further prompting

q - Quit the program

These options are all insensitive to case.

If you're doing forced renaming (-f), this option will interactively ask you first about making any necessary backups and then renaming the original target. If you decline to do the backup renaming, but accept the renaming of the original target, the file or directory that already exists with that name will be lost!.


Turn off backups during forced renaming.

(Default: Do Backups)

Ordinarily, tren will refuse to do a renaming if the new name for a file- or directory already exists. You can override this with the -f (forced renaming) option. By default, forced renaming makes a backup copy of the existing file (by appending .backup to its name or some other suffix you specify with the -S option) before doing the renaming. This prevents existing files from being lost due to a renaming. The -b option inhibits backups and allows renaming over existing file- and directory names, thereby losing the original file- or directory.


Do case sensitive renaming

(Default: This is the program default)

This option is provided so you can toggle the program back to its default behavior after a previous -c on the command line.

This option is observed both for literal and regular expression-based renaming (-x). .


Collapse case when doing string substitution.

(Default: Search for string to replace is case sensitive)

When looking for a match on the old string to replace, tren will ignore the case of the characters found in the file name. For example: -cr Old=NEW Cold.txt fOlD.txt

This renames both files to CNEW.txt and fNEW.txt respectively. Notice that the new (replacement) string's case is preserved.

This option is observed both for literal and regular expression-based renaming (-x).


Dump debugging information

(Default: Off)

Dumps all manner of information about tren internals - of interest only to program developers and maintainers. This option provides internal program state at the time it is encountered on the command line. For maximum debug output, place this as the last (rightmost) option on the command line, right before the list of files and directories to rename. You can also place multiple -d options on the command line to see how the internal tables of the program change as various options are parsed.

This option also shows each incremental change to a file name as each renaming request specified on the command line is applied. This can be helful when figuring out a new/complex renaming operation. This is most easily used by invoking the "quiet" and "test" modes: -tqd -r... -r... file file...
-e casetype

Force case change to casetype.

(Default: No forced case.)

This option supports a number of casetype arguments to transform the case of the file name:

c - Capitalize the file name
l - Force file name to lower-case
s - Swap case of file name characters
t - Force file name to title case
u - Force file name to upper-case

"Title case" just means that any alphabetic character following a non-alphabetic character will be capitalized: -et fee_fi_fo # -> Fee_Fi_Fo

Notice that these case transformations are a kind of special built-in renaming request with one important difference: The -i "instance" setting is ignored. That's because the -e option isn't based on replacing an "old" string like the -r renaming option, but rather operates on the file name as a whole.

There is, however, a way to limit the effect of the case forcing options because the -T or "target" option is observed. You can thus limit the which portion of the file name should have its case changed: -T4:6 -eu fee_fi_fo # -> fee_FI_fo

Force renaming even if target file or directory name already exists.

(Default: Skip renaming if a file or directory already exists by the same name as the target.)

By default, tren will not rename something to a name that is already in use by another file or directory. This option forces the renaming to take place. However, the old file or directory is not lost. It is merely renamed itself first, by appending a suffix to the original file name. (Default: .backup, but you can change it via the -S option.) This way even forced renames don't clobber existing files or directories.

-h Print help information.
-I file

"Include" command line arguments from file

It is possible to perform multiple renaming operations in one step using more than one -r option on the tren command line. However, this can make the command line very long and hard to read. This is especially true if the renaming strings are complex, contain regular expressions or Renaming Tokens, or if you make heavy use of command line toggles.

The -I option allows you to place any command line arguments in a separate file in place of- or in addition to the tren command line and/or the $TREN environment variable. This file is read one line at a time and the contents appended to any existing command line. You can even name the files you want renamed in the file, but they must appear as the last lines of that file (because they must appear last on the command line).

Whitespace is ignored as is anything from a # to the end of a line:

# Example replacement string file
# Each line appended sequentially
# to the command line

-xr t[ext]+=txt     # Appended first
-r =/MYEAR/ -r foo=bar
your.file          # Appended last

You may "nest" includes. That is, you can include file x, that includes file y, that includes file z and so on. However, its easy to introduce a "circular reference" when you do this. Suppose file z tried to include file x in this example? You'd be specifying an infinite inclusion loop. To avoid this, tren limits the total number of inclusions to 1000. If you exceed this, you'll get an error message and the program will terminate.

Note that wildcard metacharacters like * and ? that are embedded in file names included this way are expanded as they would be from the command shell.

You can define an environment variable, TRENINCL, to specify a path to search to find the named include file(s). tren will use the first (leftmost) instance of the include file it finds along this path. If none are found, tren uses the file path as passed on the command line. This allows relative- and absolute include file paths to be used along with files in an include path:

export TRENINCL=$HOME/.tren:/some/where/else
cp file1 $HOME/.tren/ -I file1 -I foo/file2 -I /foo/bar/file3 *

'file1' will be found in $HOME/.tren/
'file2' will be found relative to current dir
'file3' will be found on absolute path

Note that when defining TRENINCL, you must use the path delimiter appropriate for the operating system in question. For Windows, this is ;, For all other supported OSes, it is :.

-i instances

Specifies which "instances" of matching strings should be replaced.

(Default: 0 or leftmost)

A file may have multiple instances of the old renaming string in it. The -i option lets you specify which of these (one, several, all) you'd like to have replaced.

Suppose you have a file called foo1-foo2-foo3.foo4. The leftmost foo is instance 0. The rightmost foo is instance 3. You can also refer to instances relative to the right. So the -1 instance is the last (rightmost), -2, second from the last, and so forth.

Often, you just want to replace a specific instance:

-i :3 -r foo=boo
-i :-1 -r foo=boo

Both of these refer to the last instance of old string foo (found at foo4 in our example name).

Sometimes, you'd like to replace a whole range of instances. An "instance range" is specified using the : separator in the form:

-i first-to-replace:stop-here

Notice that the "stop-here" instance is NOT replaced. In our string above, the option:

-i 1:-1 -r foo=boo

Would change the file name to:


You can also provide partial ranges:

-i 1: # Instance 1 to end of name

-i :-2 # Instances to (not including) next-to-last

-i :   # All instances

If you provide an instance range that makes no sense or is out of range, tren will ignore the argument and leave the instance specification unchanged.

-P char

Use char as the escape symbol.

(Default: \)


Quiet mode, do not show progress.

(Default: Display progress)

Ordinarily, tren displays what it is doing as it processes each file. If you prefer to not see this "noisy" output, use the -q option. Note that this does not suppress warning and error messages.

It doesn't make much sense to use this option in test mode (-t), although you can. The whole point of test mode is to see what would happen. Using the quiet mode suppresses that output.

-R char

Use char as the separator symbol in renaming specifications.

(Default: =)

-r <old=new>

Replace old with new in file or directory names.

Use this option to specify which strings you want to replace in each file name. These strings are treated literally unless you also invoke the -x option. In that case, old is treated as a Python style regular expression.

Both old and new may optionally contain renaming tokens described later in this document.

If you need to use the = symbol within either the old or new string, simply escape it: \=

If it is convenient, you can change the separator character to something other than = via the -R option. Similarly, you can change the escape character via the -P option.

You can have multiple instances of this option on your tren command line: -r old=new -r txt:doc old-old.txt

This renames the file to:


Remember that, by default, tren only replaces the first (leftmost) instance of the old string with the new.

Each rename specification on the command line "remembers" the current state of all the program options and acts accordingly. For example: -cr A=bb -Cr B=cc ...

The A=bb replacement would be done without regard to case (both A and a would match), whereas the B=cc request would only replace B.

-S suffix

Suffix to append when making backup copies of existing targets.

(Default: .backup)

If you choose to force file renaming when the new name already exists (-f), tren simply renames the existing file or directory by appending a suffix to it. By default, this suffix is .backup, but you can change it to any string you like with the -S` option.

-T range

Target the range of characters within file name subject to renaming.

(Default: Entire file name is subject to renaming.)

Ordinarily, tren applies renaming requests and forced case conversions to the entire file name. The -T option allows you to specify some substring of the name as the "target" for renaming. The "range" argument is in the same slice notation used for the -i command. So, for example: -T1:3 -r=XYZ abcdefg # -> aXYZdefg

Similarly: -T 1:4 -es aXYZdefg # -> axyzdefg

The -T option operates on all subsequent renaming or case forcing operations to the right of it on the command line. So, if you want to go back to the default behavior of applying renaming to the entire file, you have to set the "target" back to the entire file name: -T1:4 -es -T: -rg=-X axyzdeg # -> aXYZde-X

As with the -i option, range slices that make no sense or are out of range, are simply ignored, and the portion of the file name targeted for renaming is left unchanged.


Test mode, don't rename, just show what the program would do.

tren is very powerful and capable of doing nasty things to your file and directory names. For this reason, it is helpful to test your tren commands before actually using them. With this option enabled, tren will print out diagnostic information about what your command would do, without actually doing it.

If your renaming requests contain random renaming tokens, test mode will only show you an approximation of the renaming to take place (because new random name strings are generated each time the program runs).


Print detailed program version information and keep running.

This is handy if you're capturing tren output into a log and you want a record of what version of the program was used.

-w length

Set the length of diagnostic and error output.

(Default: 80)

tren limits output to this length when dumping debug information, errors, warnings, and general information as it runs. This option is especially useful when you're capturing tren output into a log and don't want lines wrapped: -w999 ..... 2>&1 > tren.log

tren makes sure you don't set this to some unreasonably small value such that output formatting would be impossible.


Treat the renaming strings literally

(Default: This is the program default)

This option is provided so you can toggle the program back to its default behavior after a previous -x on the command line.


Treat the old string in a -r replacement as a Python style regular expression for matching purposes.

(Default: Treat the old string as literal text)



ONE MORE TIME: tren is a powerful file and directory renaming tool. Be sure you know what you're about to do. If you're not, run the program in test mode (invoke with the -t option) to see what would happen. You have been warned!

The following sections are designed for the new- or occasional tren user. They begin with the simplest of tren operations and incrementally build more and more complex examples, eventually describing all of tren's capabilities.


tren is a general purpose file and directory renaming tool. Unlike commands like mv, tren is particularly well suited for renaming batches of files and/or directories with a single command line invocation. tren eliminates the tedium of having to script simpler tools to provide higher-level renaming capabilities.

tren is also adept at renaming only part of an existing file or directory name either based on a literal string or a regular expression pattern. You can replace any single, group, or all instances of a given string in a file or directory name.

tren implements the idea of a "renaming token". These are special names you can embed in your renaming requests that represent things like the file's original name, its length, date of creation, and so on. There are even renaming tokens that will substitute the content of any environment variable or the results of running a program from a shell back into the new file name.

tren can automatically generate sequences of file names based on their dates, lengths, times within a given date, and so on. In fact, sequences can be generated on the basis of any of the file's stat information. Sequence "numbers" can be ascending or descending and the count can start at any initial value. Counting can take place in one of several internally defined counting "alphabets" (decimal, hex, octal, alpha, etc.) OR you can define your own counting alphabet. This allows you to create sequences in any base (2 or higher please :) using any symbol set for the count.

A Word About Program Defaults

tren has many options, but its defaults are designed to do two things: a) Simplify the most common operations by making them the default (no options required on the command line), and 2) Reduce the risk of accidentally modifying more of the file name than you intented. So, by default:

tren treats renaming requests literally. That is, the "old string" you specify for replacement is treated as literal text. It requires a command line option (-x) to treat it as a regular expression. However, any renaming tokens found in either the old- or new strings of a renaming request are interpreted before the renaming takes place.

tren renaming is case sensitive. If you want to ignore case, use the -c option.

tren will only replace the first (leftmost) instance of "old string" with "new string". If you want more- or different instances replaced, use the -i option.

tren will not allow you to rename a file or directory if one with the new name already exists. Such attempts will cause no change to the file or directory being processed and an error message will be displayed. This is intentional to force you to manually rename or remove the file or directory that would have been clobbered by a rename. You can override this default and force a renaming via the -f option. This will cause the orginal file or directory itself to be renamed with a .backup suffix. You can change this suffix via the -S option.

Getting Help

There are three command line options that can give you some measure of help and information about using tren:

-d Dumps debug information out to stderr. You can insert multiple instances of this option on the command line to see how the program has parsed everything to the left of it. This is primarily intended as a debugging tool for people maintaining tren but it does provide considerable information on the internal state of the program that advanced users may find useful.
-h Prints a summary of the program invocation syntax and all the available options and then exits.
-v Prints the program version number and keeps running.

Controlling Program Output

As tren runs, it produces a variety of diagnostic and status information. There are a number of options you can use to control how this works:

-q Sets "quiet" mode and suppresses everthing except error messages.
-w num Tells tren to wrap lines after num characters have been printed. If you're capturing output to a log, set this to a very high number like 999 to inhibit line wrapping.

Error and debug messages are sent to stderr. Normal informational messages are sent to stdout. If you want to capture them both in a log, try something like this (depending on your OS and/or shell): ..... 2>&1 >tren.log

Managing Complexity

As you learn more of the program features, the tren command line can get long, complex, and easy to goof up. It's also hard to remember all the various options, how they work exactly, and which specific one you need. For this reason, it is highly recommended that - once you have a renaming request working the way you like - if you plan to use it again, save it as an "include" file. That way you can reuse it easily without having to keep track of the details over and over. Instead of this:

tren.pu -c -i -1 -r .jpeg=.jpg file ...

Do this: -I jpeg-to-jpg.tren file...

What's in the jpeg-to-jpg.tren file? Just this:

# tren Command Line
# Converts '.jpeg' (in any case mixture) file name suffix to '.jpg'

# Make the replacement case insensitive
-c   # Reset this later on the command line with -C

# Only replace the rightmost instance
 -i -1

# The actual replacement request
-r  .jpeg=.jpg

Notice that you can stick comments in the file anywhere you like and that they begin with #. Notice also that the various options can be entered on separate lines so it's simpler to read the include file. If you find it useful, you can even include other include files in an include file:

# Get the jpeg -> jpg suffix renaming

-I  jpeg-to-jpg.tren

# Let's make it fancy

-i -1 -r .jpg=.fancy.jpg

If you do this, take care not to create a circular include. This can happen when an include file tries to include itself, either directly, or via another include file. tren limits the total number of includes to a very large number. If it sees that the number has been exceeded, it suspects a circular include and will issue an error message to that effect and exit.

You can insert include options anywhere you like on the command line and you can have as many as you like (up to a large number you'll never hit in practice). Each include reference will be replaced with the contents of that file at the position it appears on the command line.

If you find yourself using certain options most- or every time you use the program, you can put them in the $TREN environment variable. tren picks this up every time it starts. This minimizes errors and reduces typing tedium. Just keep in mind that some options can be overriden later on a command line, and some cannot. For instance, suppose you do this:

export TREN=-f -c

The -c option to ignore case can be undone on the command line with a -C option. However, the -f option cannot be undone.

So ... choose the options you want to make permanent in the environment variable wisely.

Renaming Basics

tren supports a variety of renaming mechanisms. The one thing they have in common is that they're built with one or more renaming requests that will be applied to one or more file- or directory names. Renaming requests look like this on the tren command line: ... -r old=new ... -r old=new ... list of files/directories

No matter how complicated they look, the basic logic of the renaming request stays the same: "When you find the string old in the file- or directory name, change it to the string new.

The old and new renaming strings are built using a variety of building blocks:

Old Strings Are Built With: New Strings Are Built With:
Literal Text Literal Text
Regular Expressions Renaming Tokens
Renaming Tokens  

You can use any of these building blocks alone or combine them to create expressive and powerful renaming schemes.

Literal String Substitution

Literal String Substitution is just that - it replaces one literal string with another to rename the target file or directory. This is the most common, and simplest way to use tren. This is handy when you have files and directories that have a common set of characters in them you'd like to change. For instance: -r .Jpeg=.jpg *.Jpeg

This would rename all files (or directories) whose names contained the string .Jpeg and replace it with .jpg. Well ... that's not quite right. Unless you specify otherwise with the -i option, only the first (leftmost) instance of ``old`` is replaced with ``new``. So, for example, if you started out with the file, My.Jpeg.Jpeg and ran the command above, you'd end up with a new file name of My.jpg.Jpeg

You can omit either old or new strings in a renaming specification, but never both.

If you omit the old string, you're telling tren to change the whole file name: -r =MyNewFilename foo  #New Name: MyNewFilename

Be careful with this one. If you apply it to a list of files or directories, it's going to try and name them all to the same name. By default, tren will refuse to overwrite an existing file name, so it will stop you from doing this. If you absolutely insist on this via the -f option, you'll get a bunch of files ending with .backup. Say you have files a, b, and c: -fr =NewName a b c

When the command completes, the files will have been renamed in this fashion:

a -> NewName.backup.backup
b -> NewName.backup
c -> NewName

If you omit the new string, you're telling tren to remove the leftmost instance of old string (or other instances via the -i option described below) from the file- or directory name. For example: -rfoo= foo1-foo2-foo3.foo4  # New name: 1-foo2-foo3.foo4

If you try to omit both old and new strings, you're effectively telling tren to change the existing file name to ... nothing (a null string). This is impossible because file names must be at least one character long. tren enforces both this minimum length AND the maximum legal length of new file names. It will print an error and exit if your renaming attempt would violate either of these limits. (As of this writing, the maximum file- or directory name length allowed by the operating systems on which tren runs is 255 characters.)

Substitution Instances

As we just saw above, sometimes the old string appears in several places in a file- or directory name. By default, tren only replaces the first, or leftmost "instance" of an old string. However, using the -i option you can specify any instance you'd like to replace. In fact, you can even specify a range of instances to replace.

Instances are nothing more than numbers that tell tren just where in the name you'd like the replacement to take place. Positive numbers means we're counting instances from the left end of the name. The leftmost instance is 0 (not 1!!!).

You can also count backwards from the right end of the string using negative numbers. -1 means the last instance, -2 means next-to-last, and so on. In summary, counting from the left starts at zero and counting from the right starts at -1.

Suppose you have a file called:


The leftmost foo1 is instance 0 of old string foo. It is also instance -4. The rightmost foo4 is instance 3 of old string foo, and also instance -1.

You can specify a single instance to replace: -i 1 -r f=b foo1-foo2-foo3.foo4 #New Name: foo1-boo2-foo3.foo4 -i -1 -r f=b foo1-foo2-foo3.foo4 #New Name: foo1-foo2-foo3.boo4

You can also specify a range of instances to replace using the notation:

-i first-to-replace:stop-here

All instances from the "first-to-replace" up to, but NOT including "the stop-here" are replaced: -i 1:3 -r f=b foo1-foo2-foo3.foo4 #New Name: foo1-boo2-boo3.foo4 -i -4:-2 -r f=b foo1-foo2-foo3.foo4 #New Name: boo1-boo2-foo3.foo4

-i : means "replace all instances": -i: -r f=b foo1-foo2-foo3.foo4 #New Name: boo1-boo2-boo3.boo4

You can also use partial range specifications: -i 1: -r f=b foo1-foo2-foo3.foo4 #New Name: foo1-boo2-boo3.boo4 -i :-2 -r f=b foo1-foo2-foo3.foo4 #New Name: boo1-boo2-foo3.foo4

Note that you cannot specify individual, non-adjacent instances. There is no way to use a single tren command to replace, say, the only the 2nd and the 4th instance of an old string. Doing that requires two renaming requests. As we'll see in the section below, the good news is that we can do them both on a single tren invocation.

Limiting Renaming To Only Part Of Name

Sometimes you just want to rename a part of a file- or directory name (aka a name "substring"). As described below, you can use a Regular Expression to do this, but this can be complicated and is often overkill for simple substitutions. tren gives you the ability to limit the renaming action to a "targeted" portion of the name using the -T option. You simply supply a "slice" describing the portion of the name to be renamed: -i: -T :3  -r=x  abcdef.text # -> xdef.text -i: -T :-4 -re=E abcdef.text # -> abcdEf.text

It's important to understand how -i and -T interact. Even though all instances of a matching old string are specified via the -i: option, the -T option that follows it limits the portion of the name being considered for renaming. For instance, in the second example, removing the -T targeting gives us: -i: -re=E abcdef.text # -> abcdEf.tExt

So, -T lets you specify what substring of the full name is a candidate for renaming. All other renaming operations like -i, -r, and so on operate only upon the substring specified by -T.

If you specify multiple renaming operations on the command line, any -T targeting will remain in effect for each renaming request. For instance: -T -1 -r=OO -r=x foo

This will yield incremental renamings of:

foo  -> foOO
foOO -> foOx   # Final name

In other words, each incremental renaming request honors the current state of the -T option. To turn off targeted renaming - that is, make the whole file name the target again - simply include -T : on the command line. All renaming requests to the right of it will then target the whole name: -T -1 -r=OO -T: -rO=x foo  # Yields: foxO

More About Slice Notation

Both the -i and -T options use "slice" notation so it's useful to understand a bit more about how "slices" are constructed.


Although both options use slice notation, they mean very different things. In the case of -i, the slice specifies which instances of an old string are to be replaced. In the case of -T, the slice defines which characters in the original file name are "targeted" for renaming.

tren is written in the Python programing language. The slice notation is lifted directly from that language. if you're a Python programmer, you can skip this section :)

Imagine you have a file name like this:


Each character in the name has an "index" or number that tells you what position is occupies in the name. You can count from the left end of the name starting with 0:

Character        Index From Left
---------        ---------------
a                0
b                1
x                8
t                9

You can also count backwards relative to the right end of the name:

Character        Index From Right
---------        ---------------=
a                -10
b                -9
x                -2
t                -1

Notice that left-relative indexes are positive numbers beginning with 0, but right-relative indexes are are negative numbers beginning at -1.

So, what's a slice? A slice is a way of specifying a range of one or more values. In the case of the -T option, "values" means "positions in the name string targeted for renaming." In the case of the -i option, "values" means which instances of a given string should be renamed.

In our example above, the bcd portion of the name could be defined several different ways:


The general form of a slice is:

first character/instance:stop on this character/instance

This can be tricky to get used to. The number on the righthand side is not included in he slice - it is where the slice ends.

There are other shortcut forms of slice notation:

 :3         # Same as 0:3
3:          # From 4th char/instance through/including end
 :          # All chars/instances are included in the slice

In short, slices are a compact way to specify a range of things. If you specify a slice that makes no sense like -4:3, tren will just ignore it and not do any consequent renaming.

Multiple Substitutions

You can put as many renaming requests on a tren command line as you like (.... well, up to the length limit imposed by your operating system and shell, anyway). As we just saw, this can be handy when a single renaming request can't quite do everything we want.

BUT ... there's a catch. In designing your renaming requests, you have to keep in mind that tren processes the command line from left to right, incrementally constructing the new name as it goes. That is, the leftmost renaming request operates on the original file- or directory name. The next renaming request to the right operates on that new name, and so on. In other words, each renaming request modifies the name produced thus far by all the renaming requests to the left of it on the command line.

For instance: -r foo=bar -r foo=baz  foo1-foo2-foo3.foo4

Produces ... wait a second ... why on earth are there two renaming requests with identical old strings on the same command line? Shouldn't this produce a final name of baz1-foo2-foo3.foo4?

Nope. After the leftmost renaming request has been processed, the new name is bar1-foo2-foo3.foo4. Remember that, by default, tren only replaces the leftmost or 0th instance of an old string. So, when the second renaming request is processed, the instance 0 of foo is now found in the string foo2. So, the final name will be, bar1-baz2-foo3.foo4.

The lesson to learn from this is that multiple renaming requests on the command line will work fine, but you have to do one of two things (or both):

  1. Make sure you're tracking what the "intermediate" names will look like as the new file name is being constructed, renaming request, by renaming request.
  2. Make sure the renaming requests operate on completely disjoint parts of the file name.


Similarly, tren remembers the last state of each option as you move from left to right on the command line. For instance: -i1 -r f=F -r o=O foo1-foo2-foo3.foo4

You might be tempted to believe that this would produce:


But it doesn't. It produces:


instead because the -i 1 appears prior to both renaming requests and thus applies to each of them. If you want the first instance of "o" to be replaced, you need a command line like this: -i1 -rf=F -i0 -ro=O foo1-foo2-foo3.foo4

This sort of thing is generally true for all options, so be sure they're set the way you want them to the left of a renaming request.

As a practical matter, this can get really complicated to track. If in doubt, it's always better to run two separate tren commands in, say, a shell script to make the renaming explicit, rather than to obscure things with clever command line trickery.

So, let's go back to our example from the previous section. We want to replace the 2nd and 4th instances of the string "foo" in our file name. We do this with two renaming requests on the same command line, considering what each one does to the name as it is encountered: -i1 -r foo=bar -i2 -r foo=bar foo1-foo2-foo3.foo4

A good way to get an idea of how incremental renamings would take place is to run tren is test and debug modes because debug will dump an incremental renaming sequence description as it goes: -tdq -rfi=fud -et fee_fi_fo

The (partial) debug output will show you this: DEBUG: Renaming Sequence: fee_fi_fo--->fee_fud_fo--->Fee_Fud_Fo

More About Command Line Pitfalls

As we just saw, you can get surprising results as tren works its way through the command line from left to right. There are other potential pitfalls here, so it's helpful to understand just how tren processes your command line, step-by-step:

  1. Prepend the contents of $TREN to the user-provided command line.

    This allows you to configure your own default set of options so you don't have to type them in every time.

  2. Resolve all references to include files.

    This has to be done before anything that follows, because include files add options to the command line.

  3. Build a table of every file name to be renamed.

    We'll need this information if any of the renaming requests use the file attribute- or sequence renaming tokens (discussed later in this document).

  4. Build a table containing each renaming request storing the current state of every program option at that point on the command line.

    This allows tren to apply options differently to different renaming requests on the same command line. This came in handy in our example of the previous section.

  5. Resolve any renaming tokens found in either the old or new portions of the renaming request.

    At this point, both old and new are nothing more than simple strings (although old may be interpreted as a regular expression rather than literally if the option to do so is in effect).

  6. Process each file found on the command line in left to right order, applying each renaming request, in the order it appeared from left to right on the command line.

Simple eh? Well, mostly it is ... until it isn't. As we just saw, incrementally building up a new name with multiple renaming requests can produce unexpected results and we have to plan for them.

Similarly, you can inadvertently accidentally give a file the wrong name entirely ... this is usually a Bad Thing.

Say you have two files, x and y. You want to rename x to y and y to z1. Well, order matters here. Say you do this: -fr x=y -r y=z1 x y

Let's see what happens in order:

  1. File x renaming:

    x -> y
    y -> z1
So, file x is renamed z1 (!)
  1. File y renaming:

    y -> z1 .... oops, x1 exists, we need a backup
      z1 -> z1.backup
    y -> z1

Um ... not quite what we wanted. However, if we shuffle around the order of renaming arguments AND the order in which to process the files, we can get what we want:  -r y=z1  -r x=y   y x

Notice that we can drop the -f option because there is no longer a naming conflict (see the next section for more about forced renaming).


Always remember" The Rightmost Renaming Request "Wins"!

The point here, as we've said already, is that you have to be very careful when constructing command lines, keeping track of options, and what order you specify both renaming requests and the files- and directories to be renamed. As always, the simple way around this is to run multiple, separate tren commands, each with its own single renaming request.

Forcing Renaming

By default, tren will not allow you to perform a renaming operation if the new name already exists. For example, say you have three files, a, aa, and b, and you try this: -r a=b a aa b

tren will skip the renaming of file a because a file named b already exists. It will, however, continue to run and rename aa, to ba.

This is designed to prevent you from accidentally clobbering files that already exist. You can, however, override this default behavior and force the renaming to take place in such situations, using the -f option. Even then, the existing file isn't lost, it is simply renamed itself by appending the suffix .backup to its original name. That way, if you made a mistake, you haven't lost the original file. So, in our example above, the command becomes: -fr a=b a aa b

When it's done, we end up with these files:

b          # The original 'a' file
b.backup   # The original 'b' file
ba         # The original 'aa' file

If you don't like the suffix, .backup, you can change it to any string (of length 1 or greater) via the -S option: -S .bku -fr a=b a aa b

Now the backed up file will be named b.bku.

tren will even backup files that are themselves backups. This can be handy if your renaming request ends up mapping more than one file- or directory name to the same new name: -fr =newname a b c

This produces files named:

newname               # The original 'c' file
newname.backup        # The original 'b' file
newname.backup.backup # The original 'a' file

You can inhibit this behavior and prevent backups with the -b option. This effectively erases the original file- or directory of that name. This is very dangerous and should rarely be used. It's better to do the backups and delete them later when you're sure you do not need them. The underlying operating system rules for renaming will still apply in this case. For instance, most OSs will not allow you rename a file over the name of an existing directory and vice versa.


The Unix mv command will allow you to move a file into a directory:

mv file dir

However, this is an mv "move" semantic, and is not properly a renaming operation. The underlying file system will not permit a file to be renamed over a directory or vice versa. tren reflects this OS semantic ... it's not intended to be a reimplementation of mv.

Ignoring Case

"Literal" string substitution means just that - tren must find an exact instance of old in the file name being renamed and replace it with new. So, the default is to do case sensitive matching. There are times, however, when you want to ignore case when doing this matching. For example, suppose you have file names with a variety of suffixes in various case combinations like .jpeg, .Jpeg, and .JPEG. Suppose you'd like these to all be changed to .jpg. Rather than having to do three separate renaming operations it's handy to just ignore case when matching the old string for replacement. That's what the -c option is for: -i -1 -c -r.jpeg=.jpg *.jpeg *.Jpeg *.JPEG

Notice that the case insensitivity only applies to the matching of the old string. Once tren has determined such a match exists, the new string is used literally with case intact.

You can turn case sensitivity on- and off for various renaming requests on the same command line. -C turns case sensitivity on, and - as we just saw - -c turns it off: -cr X=y -Cr A=b ...

The X=y renaming request will be done in a case insensitive manner, whereas the A=b will be done only on literal instances of upper case A in the target file names.

Case Transformation

Sometimes you want to actually force the case of the characters in a filename to change. You do this with the -e option. This option takes one of several arguments:

c - Capitalize the file name
l - Force file name to lower-case
s - Swap case of file name characters
t - Force file name to title case
u - Force file name to upper-case

"Title case" just means that any alphabetic character following a non-alphabetic character will be capitalized: -et fee_fi_fo # -> Fee_Fi_Fo

These case transformations are a kind of special built-in renaming request with one important difference: The -i "instance" setting is ignored. That's because the -e option isn't based on replacing an "old" string like the -r renaming option, but rather operates on the file name as a whole.

You can, however, limit what portion of the filename is "targeted" for case conversion via the -T option: -T 4:6 -et fee_fi_fo # -> fee_Fi_fo

As with all renaming requests, -e is just another incremental renaming operation on the command line: -rfi=fud -et fee_fi_fo # -> fee_fud_fo -> Fee_Fud_Fo

You can actually see these incremental transformations by specifying the -d option on the command line.

The Strange Case Of Mac OS X And Windows

Mac OS X and Windows have an "interesting" property that makes case renaming a bit tricky. Both of these operating systems preserve case in file and directory names, but they do not observe it. (It is possible to change this behavior in OS X when you first prepare a drive, and make the filesystem case sensitive. This is rarely done in practice, however.)

These OSs show upper- and lower- case in file names as you request, but they do not distinguish names on the basis of case. For instance, the files Foo, foo, and FOO, are all the same name in these operating systems, and only one of these can exist in a given directory. This can cause tren to do the unexpected when your renaming command is doing nothing more than changing case. Suppose you start with a file called Aa.txt and run this command: -rA=a Aa.txt

tren will immediately complain and tell you that the file aa.txt already exists and it is skipping the renaming. Why? Because from the point-of-view of OS X or Windows, aa.txt (your new file name) is the same as Aa.txt (your original file name). You can attempt to force the renaming: -frA=a Aa.txt

Guess what happens? Since tren thinks the new file name already exists, it backs it up to aa.txt.backup. But now, when it goes to rename the original file ... the file is gone (thanks to the backup renaming operation)! tren declares an error and terminates.

This is not a limitation of tren but a consequence of a silly design decision in these two operating systems. As a practical matter, the way to avoid this issue is to never do a renaming operation in OS X or Windows that only converts case. Try to include some other change to the file name to keep the distinction between "old name" and "new name" clear to the OS. In the worst case, you'll have to resort to something like: -rA=X Aa.txt -rX=a Xa.txt

Using Regular Expressions

Ordinarily tren treats both the old string you specify with the -r option literally. However, it is sometimes handy to be able to write a regular expression to specify what you want replaced. If you specify the -x option, tren will treat your old string as a regular expresion, compile it (or try to anyway!) and use it to select which strings to replace. This makes it much easier to rename files that have repeated characters or patterns, and groups of files that have similar, but not idential strings in their names you'd like to replace.

Say you have a set of files that are similar, but not identical in name, and you want to rename them all:


Suppose you want to rename them, replacing two or more instances of b with X. It is tedious to have to write a separate literal -r old=new string substitution for each instance above. This is where regular expressions can come in handy. When you invoke the -x option, tren understands this to mean that the old portion of the replacement option is to be treated as a Python style regular expression. That way, a single string can be used to match many cases: -x -r bb+=X *.txt

This renames the files to:


Keep in mind that a literal string is a subset of a regular expression. This effectively means that with -x processing enabled you can include both regular expressions and literal text in your "old string" specification. The only requirement is that the string taken as a whole must be a valid Python regular expression. If it is not, tren will display an error message to that effect.

For more detail on the Python regular expression syntax, see:

Because Python regular expressions can make use of the = symbol, you need a way to distinguish between an = used in a regular exression and the same symbol used to separate the old and new operands for the -r option. Where this symbol needs to appear in a regular expression, it has to be escaped like this: \=. (You can also get around this by changing the old/new separator character with the -R option.)

As with literal string renaming, regular expression renaming requests honor both the case sensitivity options (-C and -c) as well as the instance option, -i. So, for example: -x -ci -1 -r Bb+=X sbbsbbbsbbbbsbbbbbs

You'll rename the file to sbbsbbbsbbbbsXs

Changing The Renaming Separator & Escape Characters

There may be times when the default renaming separator (=) and/or escape character (\) make it clumsy to construct a renaming request. This can happen if, say, either the old- or new string in a literal renaming needs to use the = symbol many times. Another case where this may be helpful is when constructing complex regular expressions that need to make use of these characters.

The -R and -P options can be used to change the character used for renaming separator and escape character respectively. You can use any character you like (these must be a single character each), but bear in mind that the underlying operating system understands certain characters as being special. Trying to use them here will undoubtedly deeply confuse your command shell, and possibly your file system. For example, the / character is used as a path separator in Unix-derived systems. It's therefore a Really Bad Idea to try and use it as a renaming separator or escape character.

Interactive Renaming

By default, tren attempts to perform all the renaming requests on all the file- and directory names given on the command line automatically. It is sometimes helpful to work interactively wherein you're asked what to do for each proposed renaming. Interactive renaming is requested via the -a, "ask" option: -a -rfoo=Bar foo1.txt foo2.txt foo3.txt

tren will compute each file's proposed new name and ask you what you want to do. You have 4 possible choices:

N, n, or Enter - No, don't rename this file
Y, y           - Yes, rename the file
!              - Yes, rename everything further without asking
Q, q           - Quit the program

There is one slight subtlety here to watch for when doing forced renaming. As we've seen, if you select the -f option and the new file name already exists, tren will backup the existing file name before doing the renaming. In interactive mode, you will be asked whether or not to proceed with the renaming both for the file in question and for any consequenent backups. If you decline to do the backup but accept the primary renaming, this will have the same effect as the -b option: The existing file- or directory will be overwritten by the renaming operation.

If the -b option is selected in interactive mode, then you'll only be prompted for the primary file renamings (because -b suppresses the creation of backups).

An Overview Of Renaming Tokens

tren implements the notion of renaming tokens. These can be a bit complex to grasp at first, so we'll introduce them "gently" in the next few sections and then dive into the detail thereafter.

It is sometimes useful to be able to take a group of files or rename them using some property they possess like creation date, size, owner's name, and so on. This is the purpose of renaming tokens.

Renaming tokens are nothing more than special symbols that represent "canned" information tren knows about the file- or directory being renamed, information from the OS itself, and information used to sequence or order the files being renamed.

For instance, if you insert the /MYEAR/ token into a old- or new string definition, tren will replace it with the year the file or directory being renamed was last modified and use that string in the renaming process: -ryear=/MYEAR/ My-year.txt # New name: My-2010.txt

Renaming tokens can appear in either the old or new string components of a -r renaming argument. Wherever they appear, they are "resolved" by tren before any renaming is attempted. By "resolved", we mean that the renaming token will be replaced with a string that represents its meaning. For example: -i :  -r boo=/SIZE/ boors-and-boots.txt

This replaces all the instances of the literal string boo with the length of the file boors-and-boots.txt. When we're done the file will be renamed something like:


This is a silly example but it serves to illustrate the point - all renaming tokens get turned into strings before any renaming is attempted.


Deep under the covers of it all, tren really only knows how to do string replacement. That is, it can replace some old string with some new string. All the rest of the features you see are sort of syntactic sugar to make it easy for you to express your renaming intent. When tren runs, it must resolve all that fancy syntax and boil it down to creating a new file name the underling operating system knows how to produce via its renaming services.

A really handy way to use renaming tokens is to name your files in a particular order. For example, suppose you and your friends pool your vacation photos but each of your cameras uses a slightly different naming scheme. You might want to just reorder them by the date and time each picture was taken, for example. That way you end up with one coherent set of named and numbered files. You might start with something like this:

DSC002.jpg      # Bob's camera,  taken 1-5-2010 at noon
dc0234.Jpg      # Mary's camera, taken 1-5-2010 at 8am
032344.jpeg     # Sid's camera,  taken 1-3-2010 at 4pm

It would be nice to get these in order somehow. We can, by combining attribute renaming tokens (that know things about the file being renamed) and sequence renaming tokens (that know how to order all the files being renamed by some key like date, length, who owns it, and so on): -r =/MYEAR//MMON//MDAY/-MyVacation-/+MDATE::0001/.jpeg *.jp*

Every place you see something in the form /.../, think, "That is a renaming token whose value will be filled in by tren." This syntax is the same whether you're using an attribute-, system-, or sequence renaming token.

This would rename all the files in the current directory ending with .jp*. The /MYEAR/... would be replaced with the date the picture was taken ( well, actually, the date the file was last modified). The /+MDATE::0001/ refers to a starting sequence number to uniquely identify files modified on the same date. The other strings, -MyVacation- and .jpeg, are inserted literally in the final file names. After we ran this command, the files above would end up with these names:

20100103-MyVacation-0001.jpeg       # Sid's
20100105-MyVacation-0001.jpeg       # Mary's
20100105-MyVacation-0002.jpeg       # Bob's

Notice that the files taken on the same date have been sequenced by the time-of-day they were taken because we included the /+MDATE.../ sequence renaming token in our pattern. The + here means to construct the sequence in ascending order. A - would specify descending order.


Notice that there is no old string in our example above. That is, there is nothing to the left of the = symbol in the -r option. This effectively means "replace everything" in the existing file or directory name with our newly concocted naming scheme.

Of course, you don't have to replace the entire file name when using tokens. It's perfectly legitimate to replace only a portion of the existing name: -r file=/MYEAR/MMON//MDAY/-file  file-1 file.2

This would rename our files to: 20100101-file-1 and 20100101-file.2 Notice that we combined literal text and a renaming token to do this.

You can even use renaming tokens in your old string specification. For instance, suppose you manage a number of different systems and you set their system name in an environment variable called SYSNAME and this same name is used to identify backup files. You might then do something like this: -xr '/$SYSNAME/.*bku$=/FNAME/.old' *

If your system name was matrix, then the command above would only rename files whose names began with matrix and ended with bku. If your system name were morton, then the command above would only rename files whose names began with morton and ended with bku.

Notice that we combined a reference to an environment variable within a regular expression. This was done to do the match on "names beginning with... and ending with ...". Also notice that the renaming token /FNAME/ is just the original name of the file.

In order for this to work, we had to single quote the renaming request. This is because Unix shells will themselves try to replace $SYSNAME which is not what we want. If we don't single quote (thereby turning off shell variable interpolation) and run this, say, on a machine called "matrix", the command will be handed to tren looking like this: -xr /matrix/.*.bku=/FNAME/.old *

tren will then promptly error out and tell you that it doesn't know about a renaming token called /matrix/.

There are a several things to keep in mind when doing things like this:

  1. The /$SYSNAME/ in the old string is used to find the text to rename, whereas the same renaming token in the new string means insert the contents of that environment variable here.
  2. Renaming tokens are always evaluated before any regular expression processing takes place. It's up to you to make sure that when the two are combined (as we have in the example above), that the final result is still a valid Python regular expression. This may involve explicit quoting of the renaming tokens used in the old string specification.

tren has many other kinds of renaming tokens. Their structure and use is described in some detail in the section below entitled "Renaming Tokens: The Gory Details".

Renaming Token Pitfalls

As we saw in earlier sections, tren command line option and file name interaction can be tricky. It can depend on order and on whether the various renaming requests "collide" with each other as a new file name is computed. A similar potential collision exists between renaming tokens and renaming requests. Recall from "More About Command Line Pitfalls" that renaming tokens are resolved before a renaming request is processed. This means that the string substitution (literal or regular expression) of the renaming operation can conflict with the characters returned when the renaming token was resolved. For example, suppose we do this: -r =New-/FNAME/ -r My=Your MyFile.txt

The first renaming request computes the name New-MyFile.txt. However, the second renaming request further modifies this to New-YourFile.txt. In effect, the second renaming request is overwriting part of the string produced by the renaming token reference. This is an intentional feature of tren to allow maximum renaming flexibility. However, you need to understand how it works so you don't get unexpected and strange results. For example, look what happens when you reverse the order of the renaming requests in this case: -r My=Your -r =New-/FNAME/ MyFile.txt

My gets replaces with Your, but as soon as the second renaming request is processed, the whole string is thrown away and replaced with the final name New-MyFile.txt. This is yet another example of, "The Rightmost Renaming Request Wins".

Renaming Tokens: The Gory Details

As we've just seen, a renaming token is nothing more than a string representing something tren knows about. These fit in one of three categories:

  • An attribute of the file or directory being renamed
  • An attribute of the underlying operating system environment
  • A sequence that reflects some ordering principle

Renaming tokens are delimited by / characters, in the form:


tren replaces these tokens with the corresponding information (see descriptions below) wherever you indicated in either the old or new strings of a -r rename command.

Currently, tren defines a number of renaming tokens. Future releases of tren may add more of these, so it's good to periodically reread this material.

What's The Difference Between An "Attribute" And A "Sequence"?

Some renaming tokens return attributes (of either a file or the underling operating system). Some return sequences. So, what's the difference?

An "attribute" is a value associated with the file- or directory being renamed (or something about the underlying operating system). It could be the length of the file, the last year it was modified, and so on. For example, /MYEAR/ returns the year the file being renamed was last modified, /SIZE/ returns the length of the file, and /FNAME/ returns the original name of the file before renaming. So, if we do this: -r=/FNAME/-/MYEAR/-/SIZE/ file, file ...

Every file will be renamed in the form of:

original_name-YYYY-length  # Example: myfile-2010-4099

So... attributes are string substitutions wherein the string tells you something about the file or system on which you're working.

"Sequences", on the other hand, are just numbers that represent some ordering principle. Say you use the sequence renaming token ordered by size, /+SIZE::001/ to rename 10 files of different sizes: -r=/+SIZE::01/-/FNAME/ file, file, ...

This will produce a new set of files named like this:


Where, 01-original_name will be the shortest length file and 10-original_name will be the longest length file.

So... sequences are strings of numbers used to put things in some order.

You can always tell the difference between an attribute- and sequence renaming token, because sequence renaming tokens always start with either a + or - sign (to indicate ascending or descending counting respectively). This distinction is important because some attribute- and sequence renaming tokens share the same name. For instance, /FNAME/ is an attribute token representing the original name of the file before it was renamed. However, /+FNAME::003/ is a sequence renaming token that returns the position (order) of the file name in alphabetic order starting counting from 003. Although they are both based on the file name (hence the common renaming token symbol), they do very different things.

How tren Uses File Metadata

To keep track of all these attributes and/or to compute sequences, tren needs the so-called "metadata" associated with the files- and directories you've named on the command line. This metadata includes information like who owns them, how long they are, what date they were modified, and so on. (This information is commonly described in a data structure called stat. Even non-Unix systems like Windows have some version of this data structure.)

The file attribute- and sequence renaming tokens are built on this metadata, so it's worth taking a moment to understand just how it is used. tren keeps track of the following information for every file- or directory you've named on the command line:

  • The order the file appears on the command line
  • The order the file appears alphabetically
  • The original name of the file before any renaming took place
  • The date/time it was last accessed
  • The date/time it was last modified
  • The date/time its directory entry (inode) was last modified
  • The inode number for the file
  • The device number where the directory entry (inode) lives
  • The numeric group ID the file belongs to
  • The name of the group the file belongs to
  • The numeric user ID of the file owner
  • The name of the user that owns the file
  • The mode or permissions for the file
  • The number of links to the file
  • The size of the file

tren then later uses this information to resolve file attribute renaming tokens, compute the value of a particular sequence renaming token and so on as it finds them in your renaming requests. For example, a sequence renaming token based on group name will order the sequence alphabetically by group name whereas one based on group ID will order it numerically.

It is likely that you'll only be interested in a small subset of these. For completness, though, tren keeps track of all the metadata available about the files- or directories named on the command line and makes it available in the form of renaming tokens.

Most commonly, you'll find yourself using the command line, alphabetic, original name, length, and various time/date renaming tokens.

General Attribute Renaming Tokens

These tokens are derived from information about the file or directory being renamed.


Windows Users Take Note!

tren is portable across many operating systems because it is written in the Python programming language. Python mostly works the exact same way everywhere. However, Windows presents some problems because it does not quite work the same way as Unix-derived OSs do. In particular, if you need to make use of the /GROUP/ or /USER/ renaming tokens on Windows, consider installing the win32all extensions to your Windows Python installation. If you don't, tren will base its order on the generic names WindowsUser and WindowsGroup which it will apply to every file- or directory under consideration.

In any case, /DEV/, /GID/, /INODE/, /NLINK/, and /UID/ are not meaningful under Windows and default to 0. Avoid using these tokens on Windows systems, since these will return the same value for every file- or directory.

  • /DEV/    Returns File- Or Directory's Device ID

    This is the ID of the device containing the file being renamed. You might want to rename files so that all the files on a given device start with the same key. That way, their names group together in a sorted directory listing: -r=/DEV/-/FNAME/ file | dir, file | dir, ...

    You end up with a sorted directory listing that looks something like:


    The file names are still preserved in our renaming reqest above, now they're just preceded by the device ID of the where they live with a trailing - separator.

  • /FNAME/  Returns Original File- Or Directory Name

    This is the name of the file- or directory you are renaming before you apply any renaming requests. This allows you to create new names based, in part, on the old name: -r=/FNAME/-suffix  ...  # Adds "-suffix" to original name -r=prefix-/FNAME/  ...  # Adds "-prefix" to original name -r /FNAME/=newname ...  # Same as "-r=newname" -r /FNAME/=/FNAME/ ...  # Does nothing: old/new are same
  • /GID/    Returns File- Or Directory's Group ID

    This is the number for the group to which the file- or directory belongs. One way to use this is to prepend it to every file name, thereby having all files (and or directories) in the same group list together in a sorted directory listing: -r=/GID/-/FNAME/ *
  • /GROUP/  Returns File- Or Directory's Group Name

    Essentially the same as /GID/ except it returns the name of the group rather than the number. Again, this is useful when clustering names together in a sorted directory listing: -r=/GROUP/-/FNAME/ *
  • /INODE/  Returns File- Or Directory's Serial Number

    This is typically an identifier to the directory entry for the file- or directory being renamed. /DEV/ and /INODE/ taken together provide a unique systemwide identifier for the file- or directory being renamed.

  • /MODE/   Returns File- Or Directory's Permissions

    This is a numeric string that represents the permissions of the file- or directory being renamed in standard Unix format.

  • /NLINK/  Returns Number Of Links To File- Or Directory Being Renamed

    Most operating systems allow a single file to have multiple names. These names are "linked" to the instance of the file. This replacement token is a numeric string representing the number of such links.

  • /SIZE/   Returns File- Or Directory's Length In Bytes

    This is handy if you want a sorted directory listing to list all the files of the same size together. You simply prepend the file- or directory's length onto its name: -r=/SIZE/-/FNAME/ *

    Now all of the files of, say, length 23 will group together in a sorted directory listing.

  • /UID/    Returns File- Or Directory's User ID

    This is the number for the user that owns the file- or directory being renamed. One way to use this is to prepend it to every file name, thereby having all files (and or directories) owned by the same user cluster together in a sorted directory listing: -r=/UID/-/FNAME/ *
  • /USER/  Returns File- Or Directory's User Name

    Essentially the same as /UID/ except it returns the name of the user rather than the number. Again, this is useful when clustering names together in a sorted directory listing: -r=/USER/-/FNAME/ *

System Renaming Tokens

These tokens are derived from the underlying operating system and runtime environment. Notice that, because command interpreters (shells) on various systems work differently, the first two of these have to be quoted in different ways.

  • /NAMESOFAR/ Current state of new name

    tren allows multiple renaming requests to be specified on the command line . Each of these operates serially on the renaming target name: The leftmost request operates on the original name. The resulting name is handed to the next request to the right and so on.

    /NAMESOFAR/ allows the current state of a new name to be included explicitly in a renaming request. i.e., You can insert the name a renaming request starts out with into its own renaming specification: -rX=y -r=/NAMESOFAR/.text  Xray.txt

    The first renaming request transforms the name from Xray.txt to yray.txt. This is thus the "name so far" with which the second request begins. So, the second renaming request transforms the name yray.txt into yray.txt.text.

  • /$ENV/     Environment variable

    This token is replaced with the value of the environment variable ENV. If that variable does not exist, the token is replaced with an empty string: -r ='/$ORGANIZATION/'-/FNAME/ *  # Unix shells -r =/$ORGANIZATION/-/FNAME/ *    # Windows shells

    This prepends the organization's name to everything in the current directory.

  • /`cmd`/    Arbitrary command execution

    This token is replaced with the string returned by executing the cmd command. Note that newlines are stripped from the results, since they don't belong in file names. Spaces, however, are preserved.

    For instance, you might want to prepend the name of the system to all your shell scripts: -r ='/`uname -n`/'-/FNAME/ *.sh  # Unix shells -r ="/`uname -n`/"-/FNAME/ *.sh  # Windows shells

    This construct is more generally a way to synthesize renaming tokens that are not built into tren. You can write a script to do most anything you like, execute it within the /`cmd`/ construct, and plug the results into your new file name. This effectively provides tren an unlimited number of renaming tokens.


    Be very careful using this. It's possible to construct bizzarre, overly long, and just plain chowder-headed strings that make no sense in a file name using this token. Moreover, if you attempt to insert characters that don't belong in a file- or directory name (like a path separator), construct a file name that is too long (or too short), or just generally violate something about the filesystem's naming rules, this will cause tren to abort and spit out an error. However, you will not be prevented from creating file names that are legal but undesirable, such as file names that begin with the - character. In other words, be careful and be sure you know what you're doing with this renaming token.



Both of these constructs are supported directly from most Unix command shells. That is, most Unix shells will themselves dereference constructs like $ENV and `command`. There's no need to pass them as renaming tokens, you can just use the shell's capabilities: -r =/FNAME/-`uname -n`-$LOGNAME

If you do want to use the renaming token form in a Unix shell, you must single quote them to prevent the shell from "interpolating" the variables before tren is called. If you don't do this, tren will complain about encountering unknown renaming tokens: -r='/`uname -n`/'-/FNAME/ *.sh # Right -r=/`uname -n`/-/FNAME/ *.sh   # Wrong

The real reason for providing these renaming tokens at all is because the Windows command interpreter does not have an equivalent function. The only way to achieve what these do on Windows is via renaming tokens. In Windows, you also have to pay attention to quoting, particularly when there are spaces in a `cmd` renaming token: -r=/FNAME/-/`command opts args`/ ...

This causes tren to complain mightily because it thinks /`command, opts, args, are all separate (invalid) command line arguments. To avoid this problem, you need to pass the renaming token as a single command line entity via quotes: -r=/FNAME/-"/`command opts args`/"  ...
  • /RAND#/    Random Number Generator

    This generates a (quasi) random number string, # digits wide.

    This can be useful when you want to guarantee that no renaming operation will generate a new name that conflicts with an existing name: -r=/MYEAR//MMON//MDAY/-/RAND10/ *

    This generates new file names with a 10 character random number string suffix:


    In this case, just make sure the random number string is long enough to make a name collision unlikely by picking a sufficiently large #.

    # must be a positive integer greater than 0. The random number generator is reinitialized each time the program runs, so test mode operations will only show you the "shape" of the names with the embedded random number strings, not the actual strings you'll end up with.

    Another nice use of this feature is to "mask" the actual file names. Say you have a bunch of encrypted files, but you don't want a casual viewer to even know what they are or what's in them. You might do this: -r=/RAND25/ * 2>&1 >tren.log

    Now you can encrypt tren.log and send it along with the files themselves over a non-secure channel. The recipient can decrypt the log, and figure out what the original file names were, decrypt them, and store them accordingly.

Sequence Renaming Tokens

Sometimes it's useful to rename files or directories based on some property they possess like the date or time of creation, the size of the file, who owns it, and so on. That's the idea behind the attribute renaming tokens described in the previous sections.

But another really interesting use of renaming tokens is to order all the files being renamed based on one of these parameters. For instance, instead of actually embedding the date and time of creation in a file or directory name, you might want to order the files from oldest to newest with a naming convention like:


This guarantees uniqueness in the final name and also sees to it that a sorted directory listing will show you the files or directories in the order you care about.

This is the purpose of sequence renaming tokens. They give you various ways to create sequences that can be embedded in the final file or directory name.


Many sequence renaming tokens described below share the same name with an attribute renaming token described in the previous sections. That's because they are based on the same property of the file- or directory being renamed. However, it's easy to tell which is which: Sequence renaming tokens always begin with either + or - (to indicate ascending- and descending ordering respectively).

So, /GROUP/ is an attribute renaming token that returns the group name for the file. However, /+GROUP.../ is a sequence renaming token that returns a number indicating what position the file is in when all the files named on the command line are ordered by their group names.

General Format Of Sequence Renaming Tokens

Sequence renaming tokens consist of four descriptive components and have the following general format:

/OrderingType:Counting Alphabet:Counting Pattern/

         Ordering (Required):

               +  ascending
               -  descending

         Type (Required):

               The attribute used to create the ordering.

         Counting Alphabet (Optional):

               The name of the counting system to use.

         Counting Pattern (Optional):

               Establishes the first value in the counting
               sequence and/or provides a string to format
               the count.

Note that there is no space between the Ordering flag and Type.

An Ordering flag is mandatory. It will either be + to indicate an ascending count or - to indicate a descending count.

The Type is mandatory. These are documented in the section below entitled, "Types Of Sequence Renaming Tokens".

The Counting Alphabet is optional. Counting alphabets are ways to count in different bases and even to use something other than just numbers to represent the count. These are described in the section below entitled, "Let's Learn The Alphabet".

If you omit naming a specific alphabet, tren will default to counting in Decimal. Note that you cannot omit the alphabet delimiters, so the correct form of a sequence renaming token then becomes:

/OrderingType::Counting Pattern/

A Counting Pattern is optional. Counting patterns are used to do two things: Set the initial value for the count and Describe the layout of how the count should look. This is described in the section below entitled, "Counting Pattern Format".

If you omit a counting pattern, tren will start counting from the zero-th "number" in your chosen alphabet, producing a counting pattern as "wide" as necessary to count all the items being renamed. In that case, the format of a sequence renaming token becomes:

/OrderingType:Alphabet:/    # With explicit alphabet
/OrderingType::/            # With default decimal alphabet

Let's Learn The Alphabet

Sequence renaming tokens are essentially "counters" that return a number string representing where the file- or directory being renamed sits in some order - say, by time, alphabetically or on the command line.

To be as flexible as possible in creating renaming strings, it's helpful to be able to "count" in any base, and use any set of symbols when counting. For instance, you may prefer sequences of letters instead of numbers. Such a sequence might look like this:


And so on.

tren has a number of standard such "counting alphabets" built in for the most common counting situations. As described in the previous section, you specify which of these you want to use in each sequence renaming token reference on the command line. (If you omit naming a specific alphabet, the token will default to counting in Decimal.)

The built in alphabets are:

Binary     -  Counting in Base 2 using numbers
Octal      -  Counting in Base 8 using numbers
Decimal    -  Counting in Base 10 using numbers
HexLower   -  Counting in Base 16 using numbers and lower case letters
HexUpper   -  Counting in Base 16 using numbers and upper case letters
Lower      -  Counting in Base 26 using lower case letters
LowerUpper -  Counting in Base 52 using lower- then upper case letters
Upper      -  Counting in Base 26 using upper case letters
UpperLower -  Counting in Base 52 using upper- then lower case letters


The difference between a "base" and a "symbol set".

In order to make such counting-based renamings as flexible as possible, tren is built to be able to count in any base (2 or higher) and make use of any symbol set. What's the difference? The "base" tells you how many symbols there are in your counting system. In Decimal, for example, there are 10. The "symbol" set, assigns a character to represent each of those positions. In Decimal, we customarily use, "0", "1", "2", and so on. However, there is nothing magical about the symbol set. It is the base that defines the counting system. The symbol set is just an arbitarary representation. For instance, there's no reason we can count in base 10, using the symbols, ")", "!", "#", "$", ... and so on.

This ability to use any symbol set in any base makes it easy to construct counting strings that suit your particular renaming needs. You do this by defining your own, custom counting "alphabet" via the -A command line option:

-A AlphabetName:string-of-characters

Once defined, later renaming tokens on the command line can refer to it via the /...:AlphabetName:.../ syntax discussed previously.

Say we do this: -A Foo:s2X -r=/+MTIME:Foo:/ *

This will rename all the files in the current directory in ascending mtime timestamp order using the following counting scheme:


And so on. You can use most any combination of characters you like to customize your sequence renaming token output. There are a few things to keep in mind, however:

  • The counting base is determined by the number of symbols in the symbol set not what characters you use. In the example above, we're counting in base 3 irrespective of what symbols are used to represent each "number".

  • You can define as many new alphabets as you like on the command line. (Well ... up to the maximum command line length limit imposed by the shell and/or operating system you're using.)

  • The alphabet name is case sensitive. Foo, FOO, and foo are all different alphabet names (assuming they are all defined).

  • There is no requirement that the symbol set be built out of unique characters. tren does no analysis of your symbol set at all, so this is permitted (if not recommended):

    -A  Foo:abcx123xj3,m2
  • Similarly, you can populate your alphabet with any symbols you like, BUT remember they're going to be embedded in some file- or directory name. It's a good idea to make sure you avoid illegal or undesirable characters like /, \, and - in your alphabets so they don't end up getting embedded in a name (or trying to, anyway).

  • If you use non-numerical counting schemes, your sorted directory list will not reflect that order. For example, suppose you have a bunch of files in a directory, and you do this: -r=/-MTIME:LowerUpper:/ *

    Your files will get renamed in descending mtime timestamp order as:


    And so on, where a is the oldest file- or directory. However, when you do a sorted directory listing, the names beginning with upper case characters will be listed first. Why? Because directory sorting is typically based on ASCII order wherein A-Z appear before a-Z.

Counting Pattern Format

When using sequence renaming tokens, it's nice to be able to layout the resulting counting string in some consistent way. You can use an optional "counting pattern" in your sequence renaming token to do this. The renaming pattern is used to specify two things: The width of the sequence string, and, optionally, the starting value for the sequence. For instance:

Pattern      Results
-------      -------

0001    ->   0001, 0002, 0003, ...
0000    ->   0000, 0001, 0002, ...
03      ->   03, 04, 05, ...

To understand counting patterns, you have to understand a few basic rules tren uses to interpret them:

  • The number of characters (of any kind) in the pattern fix the width of the counting string. These characters need not even be in the counting alphabet: -r=/+CTIME::abcde/ *

    This produces files renamed in ascending ctime timestamp order like this:


    And so on.

  • When a count increments such that it would exceed the width of the pattern, it "rolls over" and tren issues a warning message to that effect. Using the example above, we'd get:

    0000  # Count rolls over and warning issued!

    Notice that the count rolls over in the selected counting alphabet, it does not restart from the original counting pattern. In almost every case, you should avoid roll over and make your counting pattern wide enough to hold a full count for all the files- and directories you've named on the command line. One issue here is that rolling over is possibly going to create a name collision and the renaming will either be skipped or have to be forced (with backup) using the -f option.

  • As we've seen, tren treats each position of the counting pattern as a placeholder and "eats" characters as the count goes up. This allows you great flexibility in creating renaming patterns that embed both a count and a literal string via a single sequence renaming token. You just have to make the counting pattern wide enough so that the highest count never consumes your literal string: -r=/+MTIME:HexLower:InHexMtimeOrder-0x00000/ *

    This yields new file names like this:


    Notice that the 0x string may mean "this is a hex number" to the human reader, but it is completely insignificant to tren. If the count were to get large enough - bigger than 5 digits, the 0x string itself would get overwritten. Larger still, and InHexMtimeOrder- would start to get consumed.


    We could avoid the possibility of having the count ever consume our literal text, by taking it out of the sequence renaming token and putting it in as a literal argument to the -r option, thereby separating the text from the count:


    In short, tren treats every character in a counting pattern the same - with complete indifference.

  • Well ... almost "complete indifference". When tren finds characters that are in the selected counting alphabet, it adds them to the count. In this way we start counting at some predermined initial value. Note that tren always produces sequence number starting with 0 and, unless the pattern indicates otherwise: -r=/+CMDLINE::/ a b c


    0   # Formerly a, the 1st command line argument
    1   # Formerly b, the 2nd command line argument
    2   # Formerly c, the 3nd command line argument

But say we wanted to start counting from 1 instead: -r=/+CMDLINE::1/ a b c


  1   # Formerly a, the 1st command line argument
  2   # Formerly b, the 2nd command line argument
  3   # Formerly c, the 3nd command line argument

Similarly, /+CMDLINE::101/ would produce:

101 # Formerly a, the 1st command line argument
102 # Formerly b, the 2nd command line argument
103 # Formerly c, the 3nd command line argument

Because tren is insensitive to characters outside the counting alphabet, you can produce really interesting counting patterns like this: -r=/+CMDLINE::1x0/ a b c


  1x0   # Formerly a, the 1st command line argument
  1x1   # Formerly b, the 2nd command line argument
  1x2   # Formerly c, the 3nd command line argument

If you had enough files named on the command line, the
count would eventually consume the out-of-alphabet


So, by mixing characters that are both in- and out of the counting alphabet in a counting pattern, you "prime" the sequence renaming token to start counting with a certain string. Notice that you can do this in any position within the pattern. Say you do this: -r=/+CMDLINE::x1x4/ *

This will produce a counting sequence like this:


In other words, a character in any position of the pattern that is in the counting alphabet will be added to the count.

This works for all alphabets, any base, and any symbol set: -r=/+FNAME/:Upper:+0S/ *

Yields new file names:

  • There is no notion of starting the count from a "negative number" and counting up. You can sort of synthesize this by sticking a - in front of a sequence renaming token (or at the left end of its counting pattern). Keep in mind, though, that tren only knows how to increment a count so you will always get an "increasing negative number" when you do this: -r=-/+CMDLINE::5/-/FNAME/ a b c

    Will produce new file names:


    If you want the reverse order, specify a descending sequence renaming token: -r=-/-CMDLINE::5/-/FNAME/ a b c

    Will produce new file names:


Types Of Sequence Renaming Tokens

Sequence renaming tokens are thus a way to generate an ordering based on some property common to everything being renamed. That property is used to return a string representing just where in that order a particular file- or directory appears. This string is formatted according to the counting alphabet and counting pattern embedded in the sequence renaming token as described in the previous sections.

Keep in mind that for purposes of sequencing, tren makes no distinction between a file and directory. It merely sequences based on the property you requested.


There is one very important detail to keep in mind here. When tren first starts up, it examines the metadata of every file- and directory name on the command line. It uses this to pre-create the sequences for every possible ordering (alphabetic, by date, within date, by length, and so on) whether or not every file actually ends up being renamed later on. In other words, sequences are built on the list of names passed on the command line NOT on the list of files- or directories that actually get renamed. If your renaming requests only apply to some of the file names you passed on the command line, you may find the resulting sequence unexpected. Say you have three files, a, b, and c and you do this: -rb=/FNAME/-/+FNAME::001/ b c a

Only file b has a matching old string and thus is the only file renamed. However, because it is second alphabetically of all the files named on the command line, it gets renamed to b-002. The way to avoid this surprise is to make sure any renaming request with sequence renaming tokens in it is constructed so that it applies to all the files- and directories named on the command line.

Sometimes, more than one file- or directory named on the command line maps to the same sequencing key. For example, when using the /+GROUP.../ sequence renaming token, dozens of files in a given directory may only map to a few group names. In this situation, all the names that map to the same key will be sequenced alphabetically within the key. So if a and b are in group foo and c and d are in group baz: -r=/+GROUP/::/-/FNAME/ a b c d

Will create the new names:


tren currently supports a variety of sequence renaming tokens. Note that those associated with the various OS timestamps begin with the corresponding first letter:

  • /+-ADATE:Alphabet:Pattern/    Sequence based on atime WITHIN the same date

  • /+-CDATE:Alphabet:Pattern/    Sequence based on ctime WITHIN the same date

  • /+-MDATE:Alphabet:Pattern/    Sequence based on mtime WITHIN the same date

    These return sequences within a given day. This enables renaming constructs like: -r=/MYEAR//MMON/MDAY/-/+MDATE::001/ *

    Yielding files named:

  • /+-ATIME:Alphabet:Pattern/    Sequence based on atime timestamp

  • /+-CTIME:Alphabet:Pattern/    Sequence based on ctime timestamp

  • /+-MTIME:Alphabet:Pattern/    Sequence based on mtime timestamp

    These return sequences in absolute timestamp order. For example:

    touch foo
    touch bar
    touch baz -r =/+MTIME::/-/FNAME


  • /+-CMDLINE:Alphabet:Pattern/  Sequence based on the order of appearance on the command line

    This is nothing more than the command line order: -r=/+CMDLINE/-/FNAME::01/-/FNAME/ z b a


  • /+-DEV:Alphabet:Pattern/      Sequence based on the device ID number on which the file- or directory resides

    This is the a sequence ordered by which device ID contains the file- or directory to be renamed.

    This is not supported on Windows and defaults to an alphabetic sequence equivalent to /+-FNAME.../.

  • /+-FNAME:Alphabet:Pattern/    Sequence based on alphabetic order of all targets on the command line

    This returns a sequence based on the alphabetic order of everything you've named for renaming. Note that this is done on the fully qualified path name for each argument, not just the file- or directory name itself: -r=/+FNAME::/-/FNAME/ a/z b/b



    This is because the original file name a/z sorts alphabetically before b/b.

  • /+-GID:Alphabet:Pattern/      Sequence based on the group ID number

    This returns a sequence ordered by the ID number of the group to which the file- or directory belongs.

    This is not supported on Windows and defaults to an alphabetic sequence equivalent to /+-FNAME.../.

  • /+-GROUP:Alphabet:Pattern/    Sequence based on the group name

    This returns a sequence ordered by the name of the group to which the file- or directory belongs.

    This is only supported on Windows if the win32all Python extensions are installed. Otherwise, this defaults to an alphabetic sequence equivalent to /+-FNAME.../.

  • /+-INODE:Alphabet:Pattern/    Sequence based on the inode number

    This returns a sequence ordered by the file- or directory inode numbers.

    This is not supported on Windows and defaults to an alphabetic sequence equivalent to /+-FNAME.../.

  • /+-MODE:Alphabet:Pattern/     Sequence based on permissions

    This returns a sequence ordered by the file- or directories permissions value.

  • /+-NLINK:Alphabet:Pattern/    Sequence based on the nlink count

    This returns a sequence ordered by the number of links associated with the file- or directory.

    This is not supported on Windows and defaults to an alphabetic sequence equivalent to /+-FNAME.../.

  • /+-SIZE:Alphabet:Pattern/     Sequence based on size

    This returns a sequence ordered by the size of each file- or directory.

  • /+-UID :Alphabet:Pattern/     Sequence based on the user ID number

    This returns a sequence ordered by the ID number of the user that owns the file- or directory.

    This is not supported on Windows and defaults to an alphabetic sequence equivalent to /+-FNAME.../.

  • /+-USER:Alphabet:Pattern/     Sequence based on user name

    This returns a sequence ordered by the name of the user that owns the file- or directory.

    This is only supported on Windows if the win32all Python extensions are installed. Otherwise, this defaults to an alphabetic sequence equivalent to /+-FNAME.../.


With a program as feature dense as tren, it's not possible to document every possible use case. The following examples cover many common applications of the program.



You must be running Python 2.4.x or later. tren makes use of features not supported in releases prior to this. (It may also work with Python 2.3.x but is untested on that release.) tren has not been tested with Python 3.x and is presumed not to work with it until/unless otherwise demonstrated.

As a general matter, tren should run on any POSIX-compliant OS that has this version (or later) of Python on it. It will also run on many Microsoft Windows systems. If the Windows system has the win32all Python extensions installed, tren will take advantage of them for purposes of deriving the names of the user and group that own the file or directory being renamed.

This program is EXPERIMENTAL (see the license). This means its had some testing but is certainly not guaranteed to be perfect. As of this writing, it has been run on FreeBSD, Linux, Windows XP, and Mac OS X. It has not, however, been run on 64-bit versions of those OSs.

If you have experience, positive or negative, using tren on other OS/bitsize systems, please contact us at the email address below.


tren is primarily intented for use by power users, sys admins, and advanced users that (mostly) find GUIs more of a nuisance than a help. There are times, however when it would be handy to be able to select the files to be renamed graphically. TundraWare has a freely available macro programmed file browser. It will work nicely in such applications:


Tim Daneliuk


$Id: tren.rst,v 1.201 2011/08/01 18:06:26 tundra Exp $

You can find the latest version of this program at:

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