Lrexlib 2.1 Reference Manual

Table of Contents

Introduction

Lrexlib provides bindings of the two principal regular expression library interfaces (POSIX and PCRE) to Lua 5.1.

Lrexlib builds into shared libraries called by default rex_posix.so and rex_pcre.so, which can be used with require.

Lrexlib is copyright Reuben Thomas 2000-2007 and copyright Shmuel Zeigerman 2004-2007, and is released under the MIT license.

Notes

  1. Most functions and methods in Lrexlib have mandatory and optional arguments. There are no dependencies between arguments in Lrexlib's functions and methods. Any optional argument can be supplied as nil (or omitted if it is trailing one), the library will then use the default value for that argument.

  2. This document uses the following syntax for optional arguments: they are bracketed separately, and commas are left outside brackets, e.g.:

    MyFunc (arg1, arg2, [arg3], [arg4])

  3. Throughout this document, the identifier rex is used in place of either rex_posix or rex_pcre, that are the default namespaces for the corresponding libraries.

  4. All functions receiving a regular expression pattern as an argument will generate an error if that pattern is found invalid by the used POSIX / PCRE library.

  1. The default value for compilation flags (cf) that Lrexlib uses when the parameter is not supplied or nil, is:

    • 0 for PCRE
    • REG_EXTENDED for POSIX regex library

  1. The default value for execution flags (ef) that Lrexlib uses when the parameter is not supplied or nil, is:

    • 0 for PCRE
    • 0 for standard POSIX regex library
    • REG_STARTEND for those POSIX regex libraries that support it, e.g. Spencer's.

Lrexlib Functions

match

rex.match (subj, patt, [init], [cf], [ef], [lo])

The function searches for the first match of the regexp patt in the string subj, starting from offset init, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
[init] start offset in the subject (can be negative) number 1
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string nil
Returns on success:
  1. All substring matches ("captures"), in the order they appear in the pattern. false is returned for sub-patterns that did not participate in the match. If the pattern specified no captures then the whole matched substring is returned.
Returns on failure:
  1. nil

find

rex.find (subj, patt, [init], [cf], [ef], [lo])

The function searches for the first match of the regexp patt in the string subj, starting from offset init, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
[init] start offset in the subject (can be negative) number 1
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string nil
Returns on success:
  1. The start point of the match (a number).
  2. The end point of the match (a number).
  3. All substring matches ("captures"), in the order they appear in the pattern. false is returned for sub-patterns that did not participate in the match.
Returns on failure:
  1. nil

gmatch

rex.gmatch (subj, patt, [cf], [ef], [lo])

The function is intended for use in the generic for Lua construct. It returns an iterator for repeated matching of the pattern patt in the string subj, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string nil

The iterator function is called by Lua. On every iteration (that is, on every match), it returns all captures in the order they appear in the pattern (or the entire match if the pattern specified no captures). The iteration will continue till the subject fails to match.

gsub

rex.gsub (subj, patt, repl, [n], [cf], [ef], [lo])

The function searches for all matches of the pattern patt in the string subj and substitutes the found matches according to the parameter repl (see details below).

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
patt regular expression pattern string n/a
repl substitution source string, function or table n/a
[n] maximum number of matches to search for; unlimited if not supplied number nil
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string nil
Returns:
  1. The subject string with the substitutions made.
  2. Number of matches found.
Details:

The parameter repl can be either a string, a function or a table. The function behaves differently depending on the repl type:

  1. If repl is a string then it is treated as a template for substitution, where the %X occurences in repl are handled in a special way, depending on the value of the character X:
  • if X represents a digit, then each %X occurence is substituted by the value of the X-th submatch (capture), with the following cases handled specially:
    • each %0 is substituted by the entire match
    • if the pattern contains no captures, then each %1 is substituted by the entire match
    • any other %X where X is greater than the number of captures in the pattern will generate an error ("invalid capture index")
    • if the pattern does contain a capture with number X but that capture didn't participate in the match, then %X is substituted by an empty string
  • if X is any non-digit character then %X is substituted by X
  • all parts of repl other than %X are copied to the output string verbatim.
  1. If repl is a function then it gets called on each match with the submatches passed as parameters (if there are no submatches then the entire match is passed as the only parameter). The substitution string is derived depending on the first return value of function repl:
  • if it is a string then it is used as a substitution for the current match.
  • if it is either of nothing, nil or false then no substitution is made.
  • values of other types generate an error.

Though gsub is in general consistent with the API and behavior of Lua's string.gsub, it has one extension with regards to string.gsub behavior:

  • if function repl returns more than one value and its second return value is the literal string "break", then gsub stops searching for further matches in the subject and returns.
  1. If repl is a table then the first submatch (or the entire match if there are no submatches) is used as the key and the value stored in repl under that key is used for substitution depending on its type.
  • If no value is stored under the key but repl has a metatable with the __index field set then the correspondent metamethod will be called for obtaining the value.
  • The obtained value is used for the substitution following exactly same rules as for the first return value of repl described in the above paragraph.

split

rex.split (subj, sep, [cf], [ef], [lo])

The function is intended for use in the generic for Lua construct. It is used for splitting a subject string subj into parts (sections). The sep parameter is a regular expression pattern representing separators between the sections.

The function returns an iterator for repeated matching of the pattern sep in the string subj, subject to flags cf and ef.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
subj subject string n/a
sep separator (regular expression pattern) string n/a
[cf] compilation flags (bitwise OR) number cf
[ef] execution flags (bitwise OR) number ef
[lo] [PCRE] locale string nil

On every iteration pass, the iterator returns:

  1. A subject section (can be an empty string), followed by
  2. All captures in the order they appear in the sep pattern (or the entire match if the sep pattern specified no captures). If there is no match (this can occur only in the last iteration), then nothing is returned after the subject section.

The iteration will continue till the end of the subject. Unlike gmatch, there will always be at least one iteration pass, even if there's no matches in the subject.

plainfind

rex.plainfind (subj, patt, [init], [ci])

The function searches for the first match of the string patt in the subject subj, starting from offset init.

  • The string patt is not regular expression, all its characters stand for themselves.
  • Both strings subj and patt can have embedded zeros.
  • The flag ci specifies case-insensitive search (current locale is used).
  • This function uses neither PCRE nor POSIX regex library.
Parameter Description Type Default Value
subj subject string n/a
patt text to find string n/a
[init] start offset in the subject (can be negative) number 1
[ci] case insensitive search boolean false
Returns on success:
  1. The start point of the match (a number).
  2. The end point of the match (a number).
Returns on failure:
  1. nil

new

rex.new (patt, [cf], [lo])

The functions compiles regular expression patt into a regular expression object whose internal representation is correspondent to the library used (PCRE or POSIX regex). The returned result then can be used by the methods tfind, exec and dfa_exec. Regular expression objects are automatically garbage collected.

PCRE: A locale lo may be specified.

Parameter Description Type Default Value
patt regular expression pattern string n/a
[cf] compilation flags (bitwise OR) number cf
[lo] [PCRE] locale string nil
Returns:
  1. Compiled regular expression (a userdata).

flags

rex.flags ([tb])

This function returns a table containing numeric values of the constants defined by the used regex library (either PCRE or POSIX). Those constants are keyed by their names (strings). If the table argument tb is supplied then it is used as the output table, else a new table is created.

The constants contained in the returned table can then be used in most functions and methods where compilation flags or execution flags can be specified. They can also be used for comparing with return codes of some functions and methods for determining the reason of failure. For details, see PCRE and POSIX documentation.

Parameter Description Type Default Value
[tb] a table for placing results into table nil
Returns:
  1. A table filled with the results.

config

[PCRE only. See pcre_config in the PCRE docs.]

rex.config ([tb])

This function returns a table containing the values of the configuration parameters used at PCRE library build-time. Those parameters (numbers) are keyed by their names (strings). If the table argument tb is supplied then it is used as the output table, else a new table is created.

Parameter Description Type Default Value
[tb] a table for placing results into table nil
Returns:
  1. A table filled with the results.

version

[PCRE only. See pcre_version in the PCRE docs.]

rex.version ()

This function returns a string containing the version of the used PCRE library and its release date.

Lrexlib Methods

tfind

r:tfind (subj, [init], [ef])

The method searches for the first match of the compiled regexp r in the string subj, starting from offset init, subject to execution flags ef.

Parameter Description Type Default Value
r regex object produced by new userdata n/a
subj subject string n/a
[init] start offset in the subject (can be negative) number 1
[ef] execution flags (bitwise OR) number ef
Returns on success:
  1. The start point of the match (a number).
  2. The end point of the match (a number).
  3. Substring matches ("captures" in Lua terminology) are returned as a third result, in a table. This table contains false in the positions where the corresponding sub-pattern did not participate in the match.
    1. PCRE: if named subpatterns are used then the table also contains substring matches keyed by their correspondent subpattern names (strings).
Returns on failure:
  1. nil
Notes:
  1. If named subpatterns (see PCRE docs) are used then the returned table also contains substring matches keyed by their correspondent subpattern names (strings).

exec

r:exec (subj, [init], [ef])

The method searches for the first match of the compiled regexp r in the string subj, starting from offset init, subject to execution flags ef.

Parameter Description Type Default Value
r regex object produced by new userdata n/a
subj subject string n/a
[init] start offset in the subject (can be negative) number 1
[ef] execution flags (bitwise OR) number ef
Returns on success:
  1. The start point of the first match (a number).
  2. The end point of the first match (a number).
  3. The offsets of substring matches ("captures" in Lua terminology) are returned as a third result, in a table. This table contains false in the positions where the corresponding sub-pattern did not participate in the match.
    1. PCRE: if named subpatterns are used then the table also contains substring matches keyed by their correspondent subpattern names (strings).
Returns on failure:
  1. nil
Example:
If the whole match is at offsets 10,20 and substring matches are at offsets 12,14 and 16,19 then the function returns the following: 10, 20, { 12,14,16,19 }.

dfa_exec

[PCRE 6.0 and later. See pcre_dfa_exec in the PCRE docs.]

r:dfa_exec (subj, [init], [ef], [ovecsize], [wscount])

The method matches a compiled regular expression r against a given subject string subj, using a DFA matching algorithm.

Parameter Description Type Default Value
r regex object produced by new userdata n/a
subj subject string n/a
[init] start offset in the subject (can be negative) number 1
[ef] execution flags (bitwise OR) number ef
[ovecsize] size of the array for result offsets number 100
[wscount] number of elements in the working space array number 50
Returns on success (either full or partial match):
  1. The start point of the matches found (a number).
  2. A table containing the end points of the matches found, the longer matches first.
  3. The return value of the underlying pcre_dfa_exec call (a number).
Returns on failure (no match):
  1. nil
Example:
If there are 3 matches found starting at offset 10 and ending at offsets 15, 20 and 25 then the function returns the following: 10, { 25,20,15 }, 3.

Incompatibilities with the Previous Versions

The following changes are incompatible with Lrexlib version 1.19:

  1. Lua 5.1 is required
  2. Functions newPCRE and newPOSIX renamed to new
  3. Functions flagsPCRE and flagsPOSIX renamed to flags
  4. Function versionPCRE renamed to version
  5. Method match renamed to tfind
  6. Method gmatch removed (similar functionality is provided by function gmatch)
  7. Method exec: the returned table may additionally contain named subpatterns (PCRE only)

The following changes are incompatible with Lrexlib version 2.0:

  1. match, find, tfind, exec, dfa_exec: only one value (a nil) is returned when the subject does not match the pattern. Any other failure generates an error.
Generated on: 2007-02-12 18:37 UTC.