(?=FOO)BAR (lookahead) matches BAR, but only if there is also a match for FOO starting at the same position.(?:…) is a non-capturing group: like (…), but does not count for backreferences.
#BUSYBOX GREP REGULAR EXPRESSIONS MANUAL#
See the PCRE manual for a summary of supported features. Perl code execution is only supported in Perl). Not all features of the latest version of Perl are supported by PCRE (e.g. See the Perl documentation for nice formatting with examples. PCRE are extensions of ERE, originally introduced by Perl and adopted by GNU grep -P and many modern tools and programming languages, usually via the PCRE library. PCRE (Perl-compatible regular expressions) word boundaries \b and \B, word constituents \b and \B, … Some common extensions as in BRE: \ DIGIT backreferences (notably absent in awk except in the busybox implementation where you can use $0 ~ "(.)\\1") special characters \n, \t, etc.whether the operators +?|() means exactly m.The main differences between common tools are: The consequence is that if you have a regular expression that works in one tool, you may need to modify it to work in another tool. While there is a common ground, it seems like every tool writer made some different choices. Unfortunately, for historical reasons, different tools have slightly different regular expression syntax, and sometimes some implementations have extensions that are not supported by other tools.
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