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Laurence MorganAbout 1 min


Regexp pattern matching for file system objects (eg .*\\.txt)


Returns a list of files and directories that match a regexp pattern.

Output is a JSON list.


rx pattern -> <stdout>

!rx pattern -> <stdout>

<stdin> -> rx pattern -> <stdout>

<stdin> -> !rx pattern -> <stdout>


Inline regex file matching:

cat: @{ rx '.*\.txt' }

Writing a list of files to disk:

rx '.*\.go' |> filelist.txt

Checking if files exist:

if { rx somefiles.* } then {
    # files exist

Checking if files do not exist:

!if { rx somefiles.* } then {
    # files do not exist

Return all files apart from text files:

!g '\.txt$'

Filtering a file list based on regexp matches file:

f +f -> rx '.*\.txt'

Remove any regexp file matches from a file list:

f +f -> !rx '.*\.txt'


Traversing Directories

Unlike globbing (g) which can traverse directories (eg g /path/*), rx is only designed to match file system objects in the current working directory.

rx uses Go (lang)'s standard regexp engine.

Inverse Matches

If you want to exclude any matches based on wildcards, rather than include them, then you can use the bang prefix. eg

» rx READ*                                                                                                                                                              

murex-dev» !rx .*
Error in `!rx` (1,1): No data returned.

When Used As A Method

!rx first looks for files that match its pattern, then it reads the file list from STDIN. If STDIN contains contents that are not files then !rx might not handle those list items correctly. This shouldn't be an issue with rx in its normal mode because it is only looking for matches however when used as !rx any items that are not files will leak through.

This is its designed feature and not a bug. If you wish to remove anything that also isn't a file then you should first pipe into either g *, rx .*, or f +f and then pipe that into !rx.

The reason for this behavior is to separate this from !regexp and !match.


  • rx
  • !rx

See Also

  • f: Lists or filters file system objects (eg files)
  • g: Glob pattern matching for file system objects (eg *.txt)
  • match: Match an exact value in an array
  • regexp: Regexp tools for arrays / lists of strings

This document was generated from builtins/core/io/rx_doc.yamlopen in new window.

Last update:
Contributors: Laurence Morgan,Laurence,Laurence Morgan