[Shell] Regular expressions and wildcard characters

Tag: Class begins with regular expression find parenthesis expression matches between awk

Regular expressions and wildcard characters:

1. The regular expression is used to match the qualifying string in the file , and the Regex contains the match . grep, awk, sed, and other commands can support regular expressions.

2. Wildcards are used to match the eligible file names , and the wildcard is an exact match . LS, find, CP These commands do not support regular expressions, so you can only use the shell's own wildcard character to match.

Basic Regular expression:

* Previous character matches 0 or more times

. Match any character except the line break

^ matches the beginning of the line. ^ABC matches lines that begin with ABC

$ matches the end of the line. abc$ matches lines that end with ABC

[] matches any one of the characters specified in the brackets, matching only one character. [Aeiou] matches any vowel letter, [0-9][a-z] matches a lowercase letter and a two-bit character that consists of one digit

[^] matches any character except for the characters in brackets

\ escape character. Used to cancel the meaning of a special symbol

\{n\} matches the characters in front of it exactly n times. [0-9]\{2\} 4 digits

\{n,\} matches the preceding character occurrences of no less than n times.

\{n,m\} matches the characters that precede it at least n times and appears at most m times. [a-z]\{6,8\} matches lowercase letters from 6 to 8 bits

Attention:

* represents any character in a wildcard, in which the previous character matches 0 or more times in a regular expression.

grep "A *" Exp.txt # matches all content, including line breaks (just because it can match 0 times)

grep "aa*" Exp.txt # matches a row with at least one a

grep "aaa*" Exp.txt # matches a string that contains at least two consecutive a

grep "A.. E "Exp.txt # matches words with two characters between A and E

grep "S.*e" Exp.txt # matches words with any character between A and E

grep ". *" Exp.txt # matches all content

grep "^m" Exp.txt # matches lines starting with M

grep "n$" Exp.txt # matches rows ending with n

grep "^$" Exp.txt-n # matches all blank lines,-n can display line numbers

grep "^[a-z]" Exp.txt # matches a line beginning with a lowercase letter

grep "A[bc]e" Exp.txt # matches Abe or ace

grep "^[^a-z]" Exp.txt # matches lines that do not start with a lowercase letter

grep "[^a-za-z]" Exp.txt # matches lines with characters other than letters

grep "\.$" Exp.txt # matches lines ending in.

grep "A\{2\}" Exp.txt # matches a row that appears two times consecutively

grep "[0-9]\{2,\}" Exp.txt # matches a row with two digits in succession

grep "ab\{1,3\}" Exp.txt # matches a row with 1-3 B after

[Shell] Regular expressions and wildcard characters