Linux Learning Note: Shell Foundation regular expressions

Commands frequently used in the shell for regular expressions include grep, sed, awk

The contents of the file used for testing

[email protected] ~]# VI testfile

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I like Google

It ' s Google, not gooooogle;

Some special symbols in the basic regular expressions

1) ^word represents a line beginning with Word word

[email protected] ~]# grep ^i testfile

I like Google

It ' s Google, not gooooogle;

2) word$ represents the line ending with Word word

[[email protected] ~]# grep S $ testfile

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3). The dot number represents an arbitrary character (including spaces)

[email protected] ~]# grep t.g testfile

It ' s Google, not GOoooogle;

4) \ Slash represents the escape character, and all symbols with special meanings are reversed to their own characters (including \ itself)

[[email protected] ~]# grep "\." Testfile

Nagios Core 4. 1. 1-www. Nagios. Org

5) * represents any number of occurrences of the previous character

[[email protected] ~]# grep "O*g" Testfile

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I like Google

It ' s Google, not gooooogle;

In this example, the first line only hits G, because o can occur any number of times, including 0

6). * Matches all characters, including blank lines.

[[email protected] ~]# grep ". *" Testfile

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I like Google

It ' s Google, not gooooogle;

7) [] matches any one of the characters in the brackets

[[email protected] ~]# grep "[NO]" Testfile

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It ' s Google, not GoooooGLE;

8) [^chars] CHARS can be multiple letters or ranges that do not match any of the characters in the range. Note that this is a letter, not a word

[ [email protected] ~]# grep "[^g]oo" Testfile

I like google

9) {N,m} limits the number of occurrences of the previous character. Need to add \ Escape when using

[[email protected] ~]# grep "o\{2,3\}" Testfile #当仅使用时, although the limit was 2 to 3 times, but all came out .

I like Gooogle

Not gooooooogle

It ' s Google, not gooooogle;

[[email protected] ~]# grep "Go\{2,3\}gle" Testfile #当用其他字母夹着来用, it is possible to repeat the number of occurrences

I like Gooogle

There are also {n,}, and {n}, which represent at least n times, which represent the exact number of occurrences

Linux Learning Note: Shell Foundation regular expressions