[grep profile : ]
grep is used to filter lines that contain specific charactersusage: grep ' pattern ' fileFor example: grep ' BBB ' aaa.txt--color # Search for the keyword BBB from the file Aaa.txt and highlight it.
[Regular meta-character : ]
grep can be used in conjunction with regular expressions, the following describes the use of some commonly used regular expression filter characters .
1. ^ Denotes line startgrep ' ^bbb ' aaa.txt --color # finds lines beginning with BBB from the file aaa.txt.
2. $ means end of linegrep ' bbb$ ' aaa.txt --color # finds lines ending in BBB from the file aaa.txt.
3.
. Represents a single character that can match all characters except a newline character . grep ' bbb ... ' aaa.txt --color # Find The three-character line after the BBB from the file aaa.txt, ' dots ' can match spaces.
4. * indicates that the character in front of it can appear any timegrep ' bbb.* ' aaa.txt --color # finds rows with any character following the BBB from the file Aaa.txt .
5. + indicates that the character in front of it must appear at least oncegrep-e ' bbb.+ ' aaa.txt--color # finds rows from file Aaa.txt that appear at least one character after the BBB .
6. Indicates that the character in front of it may or may not be
grep-e ' bbbc? ' aaa.txt--color # Find rows with BBB or aaa.txt from file Bbbc . Note: grep does not support the +,? Two metacharacters, and if you want to use it, you can only use the extended grep (egrep or GREP-E)
7. [] means match a character, the character that appears in [] is or the relationshipgrep ' ^[bb]bb ' aaa.txt--color # finds lines beginning with BBB or BBB from the file Aaa.txt . grep ' [0-9] ' aaa.txt--color # Find rows containing numbers from file Aaa.txt grep-p ' \d ' aaa.txt--color # Find rows with numbers from File Aaa.txt,-p means regular expressions using Perl \d represents a number, \d represents a non-numeric\s represents a space or tab, \s means not a space or tab\w represents any character (uppercase and lowercase letters, numbers, underscores), and \w is not a letter, number, or underscore.
Note: ^ appears in [] outside the words ' start ', if it appears in [] the words ' negative 'grep ' ^[^bb]: ' Aaa.txt--color # finds lines from file aaa.txt that do not start with B or B, and are followed by two characters .
8. \< matches the beginning of a word
grep ' \<tom ' aaa.txt--color # Find the line from the file aaa.txt that starts with Tom .
9. \> matches the beginning of a word
grep ' \>tom ' aaa.txt--color # finds the line from the file aaa.txt that the word ends with Tom .
10. Match a word, not part of a string
grep ' \btom\b ' aaa.txt--color # Find the line that contains the word tom from the file Aaa.txt, if it's atomb or something like that, ignore it..
11. Use \ (\) to label, the back of the reference to use \ n (is a number), \1 means the first one is caused by the
grep ' \ (tom\) ... \1 ' aaa.txt--color # looks for Tom from the file Aaa.txt, and it's followed by three characters, then there's a Tom line. For example: Tomxxxtom
\{n\} indicates that the preceding character will appear n times
grep ' tomx\{3\} ' aaa.txt--color # find tomx from File Aaa.txt, x to appear 3 times, such as: Tomxxxgrep ' tomx\{3,\} ' aaa.txt--color # find tomx from file Aaa.txt, x must appear at least three times, such as tomxxx or tomxxxxgrep ' tomx\{3,4\} ' aaa.txt--color # Find tomx from File Aaa.txt, X appears 3 or 4 times, such as tomxxx or tomxxxx
