fop_lang

Fop (Filter and OPerations language) is an experimental, tiny expression language in the vein of awk and sed. This is a Ruby implementation. It is useful for simultaneously matching and transforming text input.

gem 'fop_lang'

Release Number Example

This example takes in GitHub branch names, decides if they're release branches, and if so, increments the version number.

  f = Fop('release-{N}.{N+1}.{N=0}')

  puts f.apply('release-5.99.1')
  =>           'release-5.100.0'

  puts f.apply('release-5')
  => nil
  # doesn't match the pattern

Anatomy of a Fop expression

Text Literal {Operation}

The above expression contains the only two parts of Fop (except for the wildcard and escape characters).

Text Literals

A text literal works how it sounds: the input must match it exactly. If it matches it passes through unchanged. The only exception is the * (wildcard) character, which matches 0 or more of anything. Wildcards can be used anywhere except inside {...} (operations).

If \ (escape) is used before the special characters *, { or }, then that character is treated like a text literal. It's recommended to use single-quoted Ruby strings with Fop expressions that so you don't need to double-escape.

Operations

Operations are the interesting part of Fop, and are specified between { and }. An Operation can consist of one to three parts:

  1. Matching class (required): Defines what characters the operation will match and operate on.
    • N is the numeric class and will match one or more digits.
    • A is the alpha class and will match one or more letters (lower or upper case).
    • W is the word class and matches alphanumeric chars and underscores.
    • * is the wildcard class and greedily matches everything after it.
    • /.../ matches on the supplied regex between the /'s. If you're regex contains a /, it must be escaped. Capture groups may be referenced in the operator argument as $1, $2, etc.
  2. Operator (optional): What to do to the matching characters.
    • = Replace the matching character(s) with the given argument. If no argument is given, drop the matching chars.
    • > Append the following chars to the matching value.
    • < Prepend the following chars to the matching value.
    • + Perform addition on the matching number and the argument (N only).
    • - Subtract the argument from the matching number (N only).
  3. Operator argument (required for some operators): meaning varies by operator.

More Examples

  f = Fop('release-{N=5}.{N+1}.{N=0}')

  puts f.apply('release-4.99.1')
  =>           'release-5.100.0'

  f = Fop('rel{/(ease)?/}-{N=5}.{N+1}.{N=0}')

  puts f.apply('release-4.99.1')
  =>           'release-5.100.0'

  puts f.apply('rel-4.99.1')
  =>           'rel-5.100.0'

  f = Fop('release-*{N=5}.{N+100}.{N=0}')

  puts f.apply('release-foo-4.100.1')
  =>           'release-foo-5.200.0'

  f = Fop('release-{N=5}.{N+1}.{N=0}{*=}')

  puts f.apply('release-4.100.1.foo.bar')
  =>           'release-5.101.0'

  f = Fop('{W=version}-{N=5}.{N+1}.{N=0}')

  puts f.apply('release-4.100.1')
  =>           'version-5.101.0'