UNIX® Shells by Example, Third Edition笔记2

1 egrep (Extended grep )

The main advantage of using egrep is that additional regular expression metacharacters (see Table 3.4 ) have been added to the set provided by grep. The \(\) and \{\}, however, are not allowed. (See GNU grep –E if using Linux.)

Table 3.4. egrep 's Regular Expression Metacharacters

Metacharacter Function Example What It Matches

^	Beginning-of-line anchor	'^love'	Matches all lines beginning with love.
$	End-of-line anchor	'love$'	Matches all lines ending with love.
.	Matches one character	'l..e'	Matches lines containing an l, followed by two characters, followed by an e.
*	Matches zero or more characters	'*love'	Matches lines with zero or more spaces of the preceding characters followed by the pattern love.
[ ]	Matches one character in the set	'[Ll]ove'	Matches lines containing love or Love.
[^ ]	Matches one character not in the set	'[^A–KM–Z]ove'	Matches lines not containing A through K or M through Z, followed by ove.
New with egrep:
+	Matches one or more of the preceding characters	'[a–z]+ove'	Matches one or more lowercase letters, followed by ove. Would find move, approve, love, behoove, etc.
?	Matches zero or one of the preceding characters	'lo?ve'	Matches for an l followed by either one or not any occurrences of the letter o. Would find love or lve.
a|b	Matches either a or b	'love|hate'	Matches for either expression, love or hate.
()	Groups characters	'love(able|ly) (ov)+'	Matches for lovable or lovely. Matches for one or more occurrences of ov.