General
- perl Practical Extraction and Report Language
Regular expressions
- {[()^$.|*+?\ are metacharacters (must be escaped)
- regexes consume as much input as possible (greedy by default)
- \b matches word boundary \B means not a word boundary
- \< start of a word \> end of a word
- ^ start of string $ end of string
- () grouping
- [ begin of a character class
- | this or that, alternative match
Quantifiers
-
a? match 'a' 1 or 0 times
-
a* match 'a' 0 or more times, i.e., any number of timesa+ match 'a' 1 or more times, i.e., at least oncea{n,m} match at least n times, but not more than m times.a{n,} match at least n or more timesa{n} match exactly n times
Not Greedy
- a?? match 'a' 1 or 0 times smallest match
- a*?, a+?, a{n,m}? work similarly for the corresponding quantifier
Lookahead ( ~ logical AND)
- (?=pattern) consumes nothing only if pattern matches
- (?!pattern) consumes nothing only if pattern does not match
Lookbehind (must be of fixed size)
- (?<=pattern) consumes nothing only if pattern matches on the left side
- (?<!pattern) consumes nothing only if pattern does not match on the left side
Character classes
- . [^\n]
- \s [\x20\f\t\r\n] \S [^\s] (negation of \s)
- \w [A-Za-z0-9_] \W [^\w] (negation of \w)
- \d [0-9] \D [^\d] (negation of \d)
- \l [a-z] \L [^\l] (negation of \l)
- \u [A-Z] \U [^\u] (negation of \u)
Escape sequences
- \f form feed
- \n newline
- \r return
- \t tabulator
- \v vertical tabulator
Variables
- $_ default variable
- $0 program name
- $/ input separator
- $\ output separator
- $| autoflush
- $! sys/libcall error
- $@ eval error
- $$ process ID
- $. line number
- @ARGV command line args
- @INC include paths
- @_ subroutine args
- %ENV environment
