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| • Regexp Usage: | How to Use Regular Expressions. | |
| • Regexp Operators: | Regular Expression Operators. |
This appendix is derived from the gawk-3.0.0 and regex-0.12
manuals.
A regular expression, or regexp, is a way of describing a set of strings. The simplest regular expression is a sequence of letters, numbers, or both. Such a regexp matches any string that contains that sequence. Thus, the regexp ‘foo’ matches any string containing ‘foo’. Other kinds of regular expressions let you specify more complicated classes of strings.
Gcal uses exactly one of the following regular expression programming libraries respectively methods, and that in the decreasing priority how it is chosen at configuration time, or better, compile time of the software:
| No. | Function | Symbol |
| 1. | GNU re_compile_pattern() and regex.h | GNU-REGEX |
| 2. | POSIX regcomp() and regex.h | POSIX-REGEX |
| 3. | BSD re_comp() | BSD-REGEX |
| 4. | System V regcmp() | SysV-REGEX |
| 5. | Henry Spencer V8 regcomp() and regexp.h | V8-REGEX |
| 6. | Pattern matching is supported, but without metacharacters | NO-REGEX |
Try ‘gcal --version’ for detecting the kind of regular expression programming library respectively method that is burned in your Gcal program!