PERL

Perl programming language

perl: Practical Extraction and Report Language

Regular expressions

• {[()^$.|*+?\ are meta-characters (must be escaped)
• regexps 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 times
• a+ match 'a' 1 or more times, i.e., at least once
• a{n,m} match at least n times, but not more than m times.
• a{n,} match at least n or more times a{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