Regular Expressions

The world of regular expressions isn't as simple as it could be: there exist many versions of them: POSIX define Basic (BRE) and Extended Regular expressions, and in addition every language and tool tries to come up with its own enhanced set (Perl, GNU utils, emacs, ...)
This an incomplete, perhaps not even correct short reference list of some common denominator of regular expressions. No idea where I got it from ...

The Metacharacters of Regular Expression

Character	Meaning
\	Turn off the special meaning of the next character
^	Indicate the beginning of the line
$	Indicate the end of the line
.	Any single character
*	Any number of occurances of the previous character
[ ]	Any one of the characters inside the square brackets
[^ ]	Any one of the characters not inside the square brackets
	Tagged regular expression

The Syntax of Regular Expression

The syntax of regular expression is basically the combination of the metacharacters and the regular characters. For example:

^My matches line starting with the word "My"
finally$ matches ending with the word "finally"
^I am a boy$ matches the whole line of the sentence "I am a boy"
\$10 matches "$10", meaning of $ is turned off
t.e matches "t" followed by any one character and then an "e"
my* matches "m" and followed by any number of occurances of "y"
th.* matches "th" and followed by any characters including no character
[124] matches one of "1" or "2" or "4"
[12-46] matches one of "1" or "2" or "3" or "4" or "6". Expanded as "2-4", not twelve to fortysix.
[^abc] matches any one except "a" and "b" and "c"

Last modified on 20010115

^My	matches line starting with the word "My"
finally$	matches ending with the word "finally"
^I am a boy$	matches the whole line of the sentence "I am a boy"
\$10	matches "$10", meaning of $ is turned off
t.e	matches "t" followed by any one character and then an "e"
my*	matches "m" and followed by any number of occurances of "y"
th.*	matches "th" and followed by any characters including no character
[124]	matches one of "1" or "2" or "4"
[12-46]	matches one of "1" or "2" or "3" or "4" or "6". Expanded as "2-4", not twelve to fortysix.
[^abc]	matches any one except "a" and "b" and "c"