15. Self-Learning Linux path: Text Processing tools Grep,eprep and Fgrep

Text Processing Tools Grep,eprep and Fgrep:

grep: (Global search regular expression and print out of the line), full search of regular expressions and display of corresponding rows

Text Search Tool: line-by-line search of target files based on user-specified text patterns, showing rows that can be matched by patterns

Format: grep [options] ' PATTERN ' file,..... Text Filter

--color=auto: Add color to the pattern you match to

Example: #grep--color=auto boot/etc/rc.d/rc.sysinit

　　　　

Build pattern: Called a regular expression, is a pattern written by a type of character (pattern)

Metacharacters: does not represent the meaning of the character itself, for the description of the additional functionality

Basic regular expressions and extended regular expressions:

Basic Regular Expressions: grep

Extended Regular expression: grep-e

Matching mechanism:

1. Match any single character:.

#grep "B.. T "/etc/passwd

#grep--color=auto ' r. T '/etc/passwd

2. Number of occurrences: used to specify the number of occurrences of the preceding character

*: Any time

Example: X*y: Matches with the following several, such as {xxy,xy,y} * before the x can appear once, two times, multiple or 0 times

. *: Any character of any length

\?: matches the preceding character 0 or 1 times

X\?y: There are a few of the following, such as {Xy,y,xxy}, that satisfy the match

Match pattern to greedy mode

\{m\}: Matches M-Times

\{m,n\}: At least m times, up to N times

\{m,\}: At least m times

\{0,n\}: Up to n times

15. Self-Learning Linux path: Text Processing tools Grep,eprep and Fgrep