POSIX

It’s POSIX specification for regular expression in UNIX-like environment tools,such as vim,sed,awk,grep.

BRE

|Metacharacters|Meaning| |:–|:–| |.|match any one character| |\\|escape character| |[|| |^|anchor for start of characters,complement set in backet expression| |$|anchor for end of characters| |*||

note:in GNU implement,you can use ERE special metacharacters by \\. BRE tools:sed,grep

ERE

|Metacharacters|Meaning| |:–|:–| |(|| |)|| |{|| |}|| |+|| |?|| |\|||

note:ERE include all BRE metachatacters. ERE tools:awk,egrep,sed -E

POSIT character class

example: [:digit:]

PCRE

PCRE include all ERE metacharacters. PCRE used in most common program language.