nimgrep User's manual

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Author:Andreas Rumpf

Nimgrep is a command line tool for search and replace tasks. It can search for regex or peg patterns and can search whole directories at once. User confirmation for every single replace operation can be requested.

Nimgrep has particularly good support for Nim's eccentric style insensitivity (see option -y below). Apart from that it is a generic text manipulation tool.


Compile nimgrep with the command:

nim c -d:release tools/nimgrep.nim

And copy the executable somewhere in your $PATH.

Command line switches

  • To search:
    nimgrep [options] PATTERN [(FILE/DIRECTORY)*/-]
  • To replace:
    nimgrep [options] PATTERN --replace REPLACEMENT (FILE/DIRECTORY)*/-
  • To list file names:
    nimgrep [options] --filenames [PATTERN] [(FILE/DIRECTORY)*]

Positional arguments, from left to right:

  1. PATTERN is either Regex (default) or Peg if --peg is specified. PATTERN and REPLACEMENT should be skipped when --stdin is specified.
  2. REPLACEMENT supports $1, $# notations for captured groups in PATTERN.
    Danger: --replace mode DOES NOT ask confirmation unless --confirm is specified!
  3. Final arguments are a list of paths (FILE/DIRECTORY) or a standalone minus - or not specified (empty):
    • empty, current directory . is assumed (not with --replace)
      Note: so when no FILE/DIRECTORY/- is specified nimgrep does not read the pipe, but searches files in the current dir instead!
    • -, read buffer once from stdin: pipe or terminal input; in --replace mode the result is directed to stdout; it's not compatible with --stdin, --filenames, or --confirm

    For any given DIRECTORY nimgrep searches only its immediate files without traversing sub-directories unless --recursive is specified.

In replacement mode we require all 3 positional arguments to avoid damaging.


  • Mode of operation:
    --find, -f
    find the PATTERN (default)
    --replace, -!
    replace the PATTERN to REPLACEMENT, rewriting the files
    confirm each occurrence/replacement; there is a chance to abort any time without touching the file
    just list filenames. Provide a PATTERN to find it in the filenames (not in the contents of a file) or run with empty pattern to just list all files:
    nimgrep --filenames               # In current dir
    nimgrep --filenames "" DIRECTORY
      # Note empty pattern "", lists all files in DIRECTORY
  • Interprete patterns:
    PATTERN and PAT are Peg
    PATTERN and PAT are regular expressions (default)
    --rex, -x
    use the "extended" syntax for the regular expression so that whitespace is not significant
    --word, -w
    matches should have word boundaries (buggy for pegs!)
    --ignoreCase, -i
    be case insensitive in PATTERN and PAT
    --ignoreStyle, -y
    be style insensitive in PATTERN and PAT
    Note: PATERN and patterns PAT (see below in other options) are all either Regex or Peg simultaneously and options --rex, --word, --ignoreCase, and --ignoreStyle are applied to all of them.
  • File system walk:
    --recursive, -r
    process directories recursively
    follow all symlinks when processing recursively
    only search the files with the given extension(s), empty one ("--ext") means files with missing extension
    exclude files having given extension(s), use empty one to skip files with no extension (like some binary files are)
    search only files whose names contain pattern PAT
    skip files whose names contain pattern PAT
    search only files with their whole directory path containing PAT
    skip directories whose name (not path) contain pattern PAT
    abbreviations of the 4 options above
    --sortTime, -s[:asc|desc]
    order files by the last modification time (default: off): ascending (recent files go last) or descending
  • Filter file content:
    select files containing a (not displayed) match of PAT
    select files not containing any match of PAT
    process binary files? (detected by 0 in first 1K bytes) (default: on - binary and text files treated the same way)
    --text, -t
    process only text files, the same as --bin:off
  • Represent results:
    output will be given without any colors
    force color even if output is redirected (default: auto)
    select color THEME from simple (default), bnw (black and white), ack, or gnu (GNU grep)
    only print counts of matches for files that matched
    --context:N, -c:N
    print N lines of leading context before every match and N lines of trailing context after it (default N: 0)
    --afterContext:N, -a:N
    print N lines of trailing context after every match
    --beforeContext:N, -b:N
    print N lines of leading context before every match
    --group, -g
    group matches by file
    --newLine, -l
    display every matching line starting from a new line
    limit max displayed columns/width of output lines from files by N characters, cropping overflows (default: off)
    --cols:auto, -%
    calculate columns from terminal width for every line
    --onlyAscii, -@
    display only printable ASCII Latin characters 0x20-0x7E
    substitutions: 0 -> ^@, 1 -> ^A, ... 0x1F -> ^_,
    0x7F -> '7F, ..., 0xFF -> 'FF
  • Miscellaneous:
    --threads:N, -j:N
    speed up search by N additional workers (default: 0, off)
    read PATTERN from stdin (to avoid the shell's confusing quoting rules) and, if --replace given, REPLACEMENT
    be verbose: list every processed file
    --help, -h
    shows this help
    --version, -v
    shows the version


All examples below use default PCRE Regex patterns:

  • To search recursively in Nim files using style-insensitive identifiers:
    nimgrep --recursive --ext:'nim|nims' --ignoreStyle
    # short: -r --ext:'nim|nims' -y
    Note: we used ' quotes to avoid special treatment of | symbol for shells like Bash
  • To exclude version control directories (Git, Mercurial=hg, Subversion=svn) from the search:
    nimgrep --excludeDir:'^\.git$' --excludeDir:'^\.hg$' --excludeDir:'^\.svn$'
    # short: --ed:'^\.git$' --ed:'^\.hg$' --ed:'^\.svn$'
  • To search only in paths containing the tests sub-directory recursively::
    nimgrep --recursive --includeDir:'(^|/)tests($|/)'
    # short: -r --id:'(^|/)tests($|/)'
    Attention: note the subtle difference between --excludeDir and --includeDir: the former is applied to relative directory entries and the latter is applied to the whole paths
  • Nimgrep can search multi-line, e.g. to find files containing import and then strutils use pattern 'import(.|\n)*?strutils'.