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2025-04-06 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Servers >
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* the main function of grep is to retrieve content based on keywords. Egrep is an extension of grep. Egrep includes all the functions of grep.
Grep usage: grep 'keyword' search object
Common parameters:
-c retrieve the number of lines containing keywords
-I is case-insensitive (keyword)
-n display line number
-v inverted (displays lines that do not contain keywords)
-r traverse all subdirectories (used to retrieve directories)
-An retrieves the lines containing keywords and the following n lines
-Bn retrieves the lines containing keywords and the n lines above
-Cn retrieves lines containing keywords as well as upper and lower n lines
-E equals egrep
Examples of special usage:
[root@localhost ~] # grep'[0-9]'/ etc/passwd
* retrieve rows containing numbers
[root@localhost ~] # grep-v'[0-9]'/ etc/passwd
* retrieve rows that do not contain numbers
[root@localhost ~] # grep'^ [0-9]'/ etc/passwd
* retrieve lines that start with a number
[root@localhost ~] # grep'[^ 0-9]'/ etc/passwd
* retrieve rows that do not contain numbers
[root@localhost ~] # grep'^ [^ 0-9]'/ etc/passwd
* retrieve lines that do not start with a number
[root@localhost ~] # grep 'r.t' / etc/passwd
*。 Means to match any character (number, letter, symbol, space)
[root@localhost ~] # grep 'oaks' / etc/passwd
* means to match 0 or more o (the character before the * sign)
[root@localhost ~] # grep'. *'/ etc/passwd
* means to match all characters (. Represents any character, and * represents 0 or more preceding characters)
[root@localhost ~] # grep'o\ {2\}'/ etc/passwd
* o {2} indicates that the row that appears twice in search o is equal to grep 'oo' / etc/passwd,\ escape character
[root@localhost ~] # egrep'o {2}'/ etc/passwd
* same as above, you don't need to add an escape character to use egrep.
[root@localhost ~] # egrep 'oaks' / etc/passwd
The * + sign indicates that it matches one or more characters preceding the + sign (o, oo, oo... Oo)
[root@localhost ~] # egrep 'oaks' / etc/passwd
*? Represents the character before 0 or 1 question mark
[root@localhost ~] # egrep 'root | test' / etc/passwd
* conduit character: user retrieves multiple keywords
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