A Regular Expression Primer

This table breifly compares the regular exprssion capability of Perl, grep, egrep, and lex. This table does not include minimal matching, casefolding, and pattern substitution features of the various regular expression languages in each tool.

chars	action	Perl	grep	egrep	lex
abc...	Match that character (metacharacters excluded)	Perl	grep	egrep	lex
\\\.\*...	Match that metacharacter following the back slash	Perl	uses sh	uses sh	lex
""	De-meta any chars inside quotes				lex
\t,\n,\r,\f	tab, newline, return, form feed	Perl	grep	egrep	lex
.	Match any character	Perl	grep	egrep	lex (not \n)
[]	Character class	Perl	grep	egrep	lex
[^]	Inverse Character class	Perl	grep	egrep	lex
[-]	Character ranges	Perl	grep	egrep	lex
\w	Match a "word" character (alphanumeric plus "_")	Perl
\W	Match a non-word character	Perl
\s	Match a whitespace character	Perl
\S	Match a non-whitespace character	Perl
\d	Match a digit character	Perl
\D	Match a non-digit character	Perl
anchors	action	Perl	grep	egrep	lex
^	Match the beginning of the line	Perl	grep	egrep	lex
$	Match the end of the line	Perl	grep	egrep	lex
\b	Match a word boundary	Perl
\B	Match a non-(word boundary)	Perl
operators	action	Perl	grep	egrep	lex
\|	Alternation	Perl		egrep	lex
()	Grouping	Perl		egrep	lex
multiplicity	action	Perl	grep	egrep	lex
*	Greedy match 0 or more times	Perl	grep	egrep	lex
+	Greedy match 1 or more times	Perl		egrep	lex
?	Greedy match 1 or 0 times	Perl	grep	egrep	lex
{n}	Greedy match exactly n times	Perl		egrep
{n,}	Greedy match at least n times	Perl		egrep
{n,m}	Greedy match at least n but not more than m times	Perl		egrep	lex
lookAhead	action	Perl	grep	egrep	lex
/	Look ahead predicate				lex
(?= )	Look ahead predicate	Perl
(?! )	NOT Look ahead predicate	Perl

Greedy means that it trys to find the longest pattern that matches from the point where the previous pattern left off.