# Configuration file contents - Parser

# Preprocessing


The ChordPro parser has a built-in preprocessor that can be used to modify input lines on the fly.

"parser" : {
    "preprocess" : {
        // All lines.
        "all" : [],
        // Directives.
        "directive" : [],
        // Song lines (lyrics) only.
        "songline" : [],

The preprocessor can act on all lines, and/or the directive and song lines (lyrics).

Each preprocessor is a list of items each having the following keys:

  • target: a string that may occur in the line;
  • replace: each target string is replaced by this value.
  • flags: replacement flags. Default is g (global - replace all occurrences). An other useful value is gi (global, case insensitive).

For example, this will replace every occurrence of the string [Bes] by [Bb]:

{ "target" : "[Bes]",
  "replace" : "[Bb]" }

Instead of string replacement, patterns can be used. This requires basic knowledge of the regular expression patterns that are used by Perl.

To use patterns, use the key pattern instead of target. For example, this is like the above but applies to Bes, Des and Ges chords:

{ "pattern" : "\\[([BDG])es\\]",
  "replace" : "[$1b]" }

In particular when preprocessing directives it is convenient to restrict processing to some lines only. For this you can add a selector pattern:

"parser" : {
    "preprocess" : {
        "directives" : [
            { "select" : "^c(omment(_(italic|box))?|i|b)?(-\\w+!?)?[:\\s]",
              "target" : ":)",
              "replace" : ":smiley:" }

This will replace the string :) by :smiley: on comment directives only.

Note that the selector is always a pattern.

See also Unicode escape characters in input in the Hints and Tips.