UNIX® Shells by Example, Third Edition笔记2

最新推荐文章于 2024-07-11 00:27:01 发布

最新推荐文章于 2024-07-11 00:27:01 发布 · 78 阅读

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本文详细介绍了egrep的正则表达式元字符及其功能，包括行首 (^)、行尾 ($)、任意单个字符 (.)、零或多个字符 (*)、字符集匹配 ([])、非字符集匹配 ([^])、一个或多个字符 (+)、零或一个字符 (?)、选择匹配 (a|b) 和分组 (()). 通过具体示例帮助读者理解这些元字符的应用。

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.