Mass Renamer is a simple console tool to bulk rename files using either simple patterns or regex patterns. mren is the short name for it - it looks unique enough not to overlap with other commands.

Why?

My workflows often produce quite a lot of similarly named files, which I need to rename using a pattern only, not file properties. 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 and set up, especially so for small simple renamings
• most of them are GUI oriented - that's not always a desirable thing
• I wanted something as simple as possible, keeping it repeatable.

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

How to use

You can download the latest compiled executable from Releases or compile yourself (see below). Put executable anywhere you like on your PATH variable. In console call mren with 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 actually taken. If you are satisfied with the preview of action - 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.

Source mask and Rename pattern

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

• simple pattern mode (default):
  • uses substitutions:
    • %a ... %z - any number of any characters, ungreedy; remembers what it matched to be used in rename pattern;
    • %0 ... %9 - 1 or more digits, greedy; remembers what it matched to be used in rename pattern;
    • * - any number of any characters, discarded, i.e. cannot be used in rename pattern;
    • ? - any single character, discarded, i.e. cannot be used in rename pattern;
    • %% - escape % - i.e. results in single literal % symbol.
  • all other characters are treated literally;
  • simple patterns are converted into regex patterns internally; there could 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. Can be overriden with Regex Options flags right in the Source pattern (see Specify options - inline).

Example 1 - simple pattern

Say we have a number of files called something like Some title.mkv_snapshot_01.02.03.jpg (MPC-HC screenshots). We want to rename those to 01.02.03 Some title.jpg form for the sake of comparisson.

FIRST STEP - 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 like:

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

See the Would rename files: section for final results. Now we are satisfied with the preview and can add -y option to run the action:

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).

Let's do the dry run using regex (-p option):

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

NOTE: Regex pattern in the command above is intentionally simplified to not use named caption groups. If you are an advanced regex user - you can use full power of C# flavor regex.

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 be replaced with empty strings if we use normal quotes ". The program would receive .jpg instead of $2 $1.jpg if " quotes were used.

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 regex power (well, complexity too).

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 - in csproj file uncomment PublishAot, comment PublishSingleFile. Results in ~4 MiB file, natively compiled. It won't be reliant on .NET framework.