What is a grep regular expression?
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A regular expression is just a description of a string, and string processing can only be done in combination with tools that support regular expressions.
Grep matching pattern
Grep accepts options and parameters as follows (where regex represents a regular expression)
W. Grep [option] Regex [file]
Options is mainly the following table:
Option meaning function description-i ignore case ignores case-v invert match mismatches-l file-with-match output matched file names-L file-without-match output mismatched file names-number of c count output matches (lines)-n number output matches lines while adding the file name and the number of lines in the file name-h no-filename suppresses the output of the file name
Suppose there are three files-del1, del2, del3-the contents are as follows
Examples
Getting started with grep regular expressions in Linux getting started with grep regular expressions in Linux
Special character
Symbolic meaning example ^ start mark "^ abc" satisfy example abc, abcd^ not (in []) "[^ abc]" satisfy example: ddd, mpd$ end tag "abc$" satisfy example abc, mmabc. Any character "A.C" satisfies the examples abc, fapcc\ "\ matches the word ending" abc\ > "abc, pmrabc | or" AAA | BBB "satisfies the examples AAA, BBBpp
Range
Examples of symbolic meaning? Match the previous character 0 or 1 time "abc?" Satisfied examples ab and mabcd* match previous character ≥ 0 times "abc*" examples abbb and abcdk+ match previous character ≥ 1 times "abc+" examples abcd, abcccdd {} {m}, {m,}, {m,}, { N} is the example abcccc or abcccccc that matches the previous character m times, m to n times, ≥ m times, ≤ n times "abc\ {3jue 5\}", respectively, if it is not in the range. Choose one. If it is a range, select one of the examples satisfied by "m [ABC] p" in the range, acpd;m [1-9] p satisfied example m8pp (), put all the elements of the candidate in (), and use | separate the examples a1bc and mba3bcd satisfied by "a (1 | 2 | 3) bc".
Note: {} needs to be transferred in the Zheng expression, but {} () does not.
Note the example of understanding the {} scope:
Standard character class
Character class defines [: alnum:] letters and numbers, equivalent to [A-Za-z0-9] [: word:] [: alnum:] and underscore _ [: alpa:] letters, equivalent to [A-Za-z] [: digit:] numbers, equivalent to [0-9] equivalent to [: xdigit:] hexadecimal characters, equivalent to [0-9A-Fa-f equivalent] [: blank:] spaces and tabs [: graph:] visible characters By expanding 33x126 [: lower:] lowercase letters [: upper:] uppercase letters [: print:] printable characters [: space:] blank characters, equivalent to [\ t\ r\ n\ v\ f] [: punct:] punctuation [: cntrl:] ASCII control code, including characters 0x31 and 127. all the contents of the article "what is grep regular expressions"? thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!
