Metacharacters are characters that have special meaning when used in a RegExp.
\
This metacharacter indicates that the following character is not a metacharacter. It matches a literal occurrence in a test string of a character not normally interpreted literally in a regexp.
^
This matches the beginning of a string.
$
This matches the end of a string.
.
This matches any single character, including '\n'. The only character not matched (under strict POSIX) is '\0', the NUL character.
[]
Matches any single character that is included between '[' and ']'.
Certain characters need to be escaped with the '\' metacharacter: '[\\\]\-\^]' would match '\', ']', '-' or '^'.
Matches any single character whose code is included in the range. For example, '[0-9]' matches any decimal digit, while '[I-N]' matches 'I', 'J', 'K', 'L', 'M' or 'N'. Adjacent occurrences of '-' expressions match any of the ranges denoted...'[A-HO-Z]' would match any capital letter except 'I', 'J', 'K', 'L', 'M' or 'N'.
This notation is used to denote POSIX-defined "character classes."
[:alnum:] matches any alphanumeric character.
[:alpha:] ... alphabetic
[:blank:] ... blank space and tab
[:cntrl:] ... control
[:digit:] ... decimal digit
[:graph:] ... characters that are both printable and visible
[:lower:] ... lower case alpha
[:print:] ... printable (not control)
[:punct:] ... punctuation (printable, non-alphanumeric, non-whitespace)
[:space:] ... whitespace
[:upper:] ... upper case alpha
[:xdigit:] ... hex digit
"Collating symbols" are included between '[.' and '.]'. .ch. matches the collating element ch, while [ch] matches either of the letters c or h.
This is the "equivalence class" syntax.
[e] would match any character considered equivalent to e, such
as an e with a diacritical mark.
[^]
The caret must follow the left bracket immediately. The bracketed regexp matches any character that the regexp would have matched were the caret not present.
This is a logical "or" operator. It has the lowest precedence of any regexp operator.
()
Parentheses are used as grouping symbols to override operator precedence, as in many other syntaxes.
*
Postfix operator that matches 0 or more occurrences of the operand.
+
Postfix operator that matches 1 or more occurrences of the operand.
?
Postfix operator that matches the operand or the null string.
{,}