Module: Shellwords

Relationships & Source Files
Defined in: lib/shellwords.rb


Manipulates strings like the UNIX Bourne shell

This module manipulates strings according to the word parsing rules of the UNIX Bourne shell.

The shellwords() function was originally a port of shellwords.pl, but modified to conform to the Shell & Utilities volume of the IEEE Std 1003.1-2008, 2016 Edition [1].


You can use Shellwords to parse a string into a Bourne shell friendly ::Array.

require 'shellwords'

argv = Shellwords.split('three blind "mice"')
argv #=> ["three", "blind", "mice"]

Once you’ve required Shellwords, you can use the #split alias String#shellsplit.

argv = "see how they run".shellsplit
argv #=> ["see", "how", "they", "run"]

They treat quotes as special characters, so an unmatched quote will cause an ArgumentError.

argv = "they all ran after the farmer's wife".shellsplit
     #=> ArgumentError: Unmatched quote: ...

Shellwords also provides methods that do the opposite. .escape, or its alias, String#shellescape, escapes shell metacharacters in a string for use in a command line.

filename = "special's.txt"

system("cat -- #{filename.shellescape}")
# runs "cat -- special\\'s.txt"

Note the ‘–’. Without it, cat(1) will treat the following argument as a command line option if it starts with ‘-’. It is guaranteed that .escape converts a string to a form that a Bourne shell will parse back to the original string, but it is the programmer’s responsibility to make sure that passing an arbitrary argument to a command does no harm.

Shellwords also comes with a core extension for ::Array, Array#shelljoin.

dir = "Funny GIFs"
argv = %W[ls -lta -- #{dir}]
system(argv.shelljoin + " | less")
# runs "ls -lta -- Funny\\ GIFs | less"

You can use this method to build a complete command line out of an array of arguments.


  • Wakou Aoyama

  • Akinori MUSHA <knu@iDaemons.org>


  • Akinori MUSHA <knu@iDaemons.org> (current maintainer)


1: IEEE Std 1003.1-2008, 2016 Edition, the Shell & Utilities volume

Class Method Summary

Class Method Details


Alias for .shellescape.

[ GitHub ]

# File 'lib/shellwords.rb', line 171

alias escape shellescape


Alias for .shelljoin.

[ GitHub ]

# File 'lib/shellwords.rb', line 201

alias join shelljoin

.shellescape(str) (mod_func) Also known as: .escape

Escapes a string so that it can be safely used in a Bourne shell command line. str can be a non-string object that responds to to_s.

Note that a resulted string should be used unquoted and is not intended for use in double quotes nor in single quotes.

argv = Shellwords.escape("It's better to give than to receive")
argv #=> "It\\'s\\ better\\ to\\ give\\ than\\ to\\ receive"

String#shellescape is a shorthand for this function.

argv = "It's better to give than to receive".shellescape
argv #=> "It\\'s\\ better\\ to\\ give\\ than\\ to\\ receive"

# Search files in lib for method definitions
pattern = "^[ \t]*def "
open("| grep -Ern -e #{pattern.shellescape} lib") { |grep|
  grep.each_line { |line|
    file, lineno, matched_line = line.split(':', 3)
    # ...

It is the caller’s responsibility to encode the string in the right encoding for the shell environment where this string is used.

Multibyte characters are treated as multibyte characters, not as bytes.

Returns an empty quoted ::String if str has a length of zero.

[ GitHub ]

# File 'lib/shellwords.rb', line 148

def shellescape(str)
  str = str.to_s

  # An empty argument will be skipped, so return empty quotes.
  return "''".dup if str.empty?

  str = str.dup

  # Treat multibyte characters as is.  It is the caller's responsibility
  # to encode the string in the right encoding for the shell
  # environment.
  str.gsub!(/[^A-Za-z0-9_\-.,:+\/@\n]/, "\\\\\\&")

  # A LF cannot be escaped with a backslash because a backslash + LF
  # combo is regarded as a line continuation and simply ignored.
  str.gsub!(/\n/, "'\n'")

  return str

.shelljoin(array) (mod_func) Also known as: .join

Builds a command line string from an argument list, array.

All elements are joined into a single string with fields separated by a space, where each element is escaped for the Bourne shell and stringified using to_s.

ary = ["There's", "a", "time", "and", "place", "for", "everything"]
argv = Shellwords.join(ary)
argv #=> "There\\'s a time and place for everything"

Array#shelljoin is a shortcut for this function.

ary = ["Don't", "rock", "the", "boat"]
argv = ary.shelljoin
argv #=> "Don\\'t rock the boat"

You can also mix non-string objects in the elements as allowed in Array#join.

output = `#{['ps', '-p', $$].shelljoin}`
[ GitHub ]

# File 'lib/shellwords.rb', line 194

def shelljoin(array)
  array.map { |arg| shellescape(arg) }.join(' ')

.shellsplit(line) (mod_func) Also known as: #shellwords, .split

Splits a string into an array of tokens in the same way the UNIX Bourne shell does.

argv = Shellwords.split('here are "two words"')
argv #=> ["here", "are", "two words"]

Note, however, that this is not a command line parser. Shell metacharacters except for the single and double quotes and backslash are not treated as such.

argv = Shellwords.split('ruby my_prog.rb | less')
argv #=> ["ruby", "my_prog.rb", "|", "less"]

String#shellsplit is a shortcut for this function.

argv = 'here are "two words"'.shellsplit
argv #=> ["here", "are", "two words"]
[ GitHub ]

# File 'lib/shellwords.rb', line 88

def shellsplit(line)
  words = []
  field = String.new
  line.scan(/\G\s*(?>([^\s\\\'\"]+)|'([^\']*)'|"((?:[^\"\\]|\\.)*)"|(\\.?)|(\S))(\s|\z)?/m) do
    |word, sq, dq, esc, garbage, sep|
    raise ArgumentError, "Unmatched quote: #{line.inspect}" if garbage
    # 2.2.3 Double-Quotes:
    #   The <backslash> shall retain its special meaning as an
    #   escape character only when followed by one of the following
    #   characters when considered special:
    #   $ ` " \ <newline>
    field << (word || sq || (dq && dq.gsub(/\\([$`"\\\n])/, '\\1')) || esc.gsub(/\\(.)/, '\\1'))
    if sep
      words << field
      field = String.new

.shellwords(line) (mod_func)

Alias for #shellsplit.

[ GitHub ]

# File 'lib/shellwords.rb', line 110

alias shellwords shellsplit


Alias for .shellsplit.

[ GitHub ]

# File 'lib/shellwords.rb', line 115

alias split shellsplit