UNIX® Shells by Example, Third Edition笔记1-优快云博客

本文详细介绍了grep命令中使用的正则表达式元字符及其用法，包括特殊字符如[^], <, >等的意义，以及如何通过标签匹配字符、使用重复模式等高级技巧。此外还列举了grep命令的常用选项，帮助用户更高效地进行文本搜索。

1. grep 's Regular Expression Metacharacters(Which I always dismissed~)

[^]

Matches one character not in the set

'[^A–K]ove'

Matches lines not containing a character in the range A through K, followed by ove.

\<	Beginning-of-word anchor	'\<love'	Matches lines containing a word that begins with love.
\>	End-of-word anchor	'love\>'	Matches lines containing a word that ends with love.

\(..\)	Tags matched characters	'\(love\)ing'	Tags marked portion in a register to be remembered later as number 1. To reference later, use \1 to repeat the pattern. May use up to nine tags, starting with the first tag at the left-most part of the pattern. For example, the pattern love is saved in register 1 to be referenced later as \1.
x\{m\} x\{m,\} x\{m,n\} ^[a]	Repetition of character x: m times, at least m times, or between m and n times	'o\{5\}' 'o\{5,\}' 'o\{5,10\}'	Matches if line has 5 occurences of o , at least 5 occurences of o , or between 5 and 10 occurrences of o .

EXPLANATION

Prints the line if it contains the word north. The \< is the beginning-of-word anchor, and the \> is the end-of-word anchor.

4. grep 's Options

Option What It Does –b Precedes each line by the block number on which it was found. This is sometimes useful in locating disk block numbers by context. –c Displays a count of matching lines rather than displaying the lines that match. –h Does not display filenames. –i Ignores the case of letters in making comparisons (i.e., upper-- and lowercase are considered identical). –l Lists only the names of files with matching lines (once), separated by newline characters. –n Precedes each line by its relative line number in the file. –s Works silently, that is, displays nothing except error messages. This is useful for checking the exit status. –v Inverts the search to display only lines that do not match. –w Searches for the expression as a word, as if surrounded by \< and \>. This applies to grep only. (Not all versions of grep support this feature; e.g., SCO UNIX does not.)