A simple console tool to bulk rename files using either glob-like or regex patterns.

Why?

My workflows often produce quite a lot of similarly named files, which I need to rename using a pattern. Doing that manually is tedious.

There are quite a lot of tools for bulk renaming on Windows. Problem is:

• they are too difficult, with miriad of options, which makes them difficult to use
• most of them are GUI oriented - that's not always a desirable thing
• I wanted something as simple as possible, keeping it repeatable.

That was my reasoning to write this tool for my own usage.

You are free to use it as you wish. Any suggestions or pull requests are welcome.

How?

mren is the short name for Mass Renamer. mren looks to be unique enough, so that it shouldn't cause overlaps with other commands.

You can download the latest compiled executable from Releases or compile yourself (see below). Put executable anywhere you like on your PATH variable.

mren needs arguments:

• folder where to look for files (. for the current folder),
• source mask (see below),
• rename pattern (see below).

By default mren does a DRY RUN only, i.e. no action is taken. Add -y option to apply.

NOTE: Currently there's no way to undo changes. If you are using recursive -r mode or overwrite -w mode - make sure to ALWAYS DO A DRY RUN first.

For source mask and rename pattern - there are 2 modes:

• glob-like (default):
  • uses substitutions:
    • %A ... %Z - any number of any characters, ungreedy;
    • %0 ... %9 - 1 or more digits, greedy;
    • * - any number of any characters, omitted, i.e. cannot be used in rename pattern;
    • ? - any single character, omitted, i.e. cannot be used in rename pattern;
    • %% - results in single literal %, escape.
  • all other characters are treated literally;
  • are converted to regex patterns internally; there might be some bugs with this conversion.
• regex patterns mode (-p option):
  • uses .NET (C#) regex patterns and substitutions syntax for both source mask and rename pattern; refer either to Microsoft docs or to regex101.com C# docs for regex syntax details.

In both modes we must match a full relative (to target folder) name string, so start (^) & end ($) anchors are added in the background. You don't need to add them.

Also, case INsensitive matching is used, hard-coded for now.

Example 1 - glob-like

Say we have a files called something like Some title.mkv_snapshot_01.02.03.jpg. We want to rename those to 01.02.03 Some title.jpg form.

With glob-like (default) patterns we can do a preview:

mren . '%A.mkv_snapshot_%B.jpg' '%B %A.jpg'

NOTE: if mren.exe is not on your PATH variable - you might need to either run as ./mren.exe if the file is located in the current folder, or to use a full path to the executable.

Which gives us output:

Scanning for files in ".", using patterns "%A.mkv_snapshot_%B.jpg" ---> "%B %A.jpg".

Sample match:
  "Some title.mkv_snapshot_01.02.03.jpg"
  1: A = "Some title"
  2: B = "01.02.03"

Would rename files:
  "Some title.mkv_snapshot_01.02.03.jpg" ···> "01.02.03 Some title.jpg"

Files matched: 1 out of 1 found
Files to be renamed: 1

Now we have made sure that the result is indeed what we wanted - we can add -y option to run the action. Using glob-like that would be:

mren . '%A.mkv_snapshot_%B.jpg' '%B %A.jpg' -y

Example 1 - regex patterns

We can do the same thing as before using regex pattern and substitution directly (-p option).

Regex in command below is not using named caption groups - this is done intentionally to simplify patterns. Let's do the dry run using regex (-p option):

mren . '(.*)\.mkv_snapshot_(.*)\.jpg' '$2 $1.jpg' -p

NOTE the single quotes ' used in the command above - shells (PowerShell here) can interfere with program execution by substituting environment variables. $1 and $2 in this case would most likely be replaced with empty strings if we use normal quotes ". The program would actually get .jpg instead of $2 $1.jpg.

We'll get a similar output from regex:

Scanning for files in ".", using patterns "(.*)\.mkv_snapshot_(.*)\.jpg" ---> "$2 $1.jpg".

Sample match:
  "Some title.mkv_snapshot_01.02.03.jpg"
  1: 1 = "Some title"
  2: 2 = "01.02.03"

Would rename files:
  "Some title.mkv_snapshot_01.02.03.jpg" ···> "01.02.03 Some title.jpg"

Files matched: 1 out of 1 found
Files to be renamed: 1

The only difference is that we now have full control, including caption groups naming.

Syntax

mren syntax help that you can get via the program itself:

Description:
  Mass Renamer - a tool to rename files in bulk using either glob-like or regex patterns.

Usage:
  mren <TargetFolder> <SourceMask> <RenamePattern> [options]

Arguments:
  <TargetFolder>   The target folder where to rename files. Relative and absolute paths could be used.
  <SourceMask>     The source mask for matching files.
                   In glob-like mode (default) pattern must match full filename. Pattern supports named matches in form of %A ... %Z for any text, %0 ... %9
                   for numeric matches, %% for % escaping. You can also use '*' and '?' as wildcards, but those will be omitted in the result.
                   Alternatively you can use '-p' flag and use C# regex pattern directly.
  <RenamePattern>  The pattern to rename files to.
                   Glob-like pattern (default) allows to use named matches from SourceMask in form of %A ... %Z, %0 ... %9. You can use %% for % escaping in
                   this mode.
                   Alternatively you can use '-p' flag and use C# regex substitutions directly.

Options:
  -y, --apply      Apply changes. Dry run otherwise.
  -r, --recursive  Process files recursively (with sub-folders).
                   If specified - filename relative to TargetFolder will be used.
                   You SHOULD do a dry run (without '-y'), as logic is a bit different.
  -p, --pattern    Treat SourceMask and RenamePattern as regex PATTERNS directly. '-p' to avoid confusion with recursive.
  -w, --overwrite  Overwrite files during renaming, if target already exists.
                   CARE !!! DESTRUCTIVE !!!
  --version        Show version information
  -?, -h, --help   Show help and usage information

Compilation from sources

I've set up a single-file publishing with only en-US locale, reliant on .NET 8.0. To get the executable yourself (~350 KiB):

• clone the repo
• go into solution or project folder
• run dotnet publish (.NET 8.0 SDK must be installed)

Other build options:

• Build a self-contained executable - set SelfContained to true in csproj file. Results in ~60 MiB file. It won't be reliant on .NET framework. Could be trimmed to reduce the size.
• Build an NativeAOT executable - uncomment PublishAot, comment PublishSingleFile in csproj file. Results in ~4 MiB file, natively compiled. It won't be reliant on .NET framework.