grep Demo

　　最近在学习Linux的几个非常强大的命令awk, sed, grep. 之前对这些命令只是有非常皮毛的了解.

最近稍微深入的对这些命令进行一些学习.grep的主要功能如下:

　　@1: 正则匹配文件中的某个(某些)字符串.

　　@2: grep具备递归搜索文件/目录(文件的内容)功能.

#!/bin/bash
#File: grepDemo.sh
#Author: lxw
#Time: 2014-08-21
#Usage: Demonstration for grep.

main(){
    #The following 2 lines are identical.
    grep "seven" test.txt|wc -l
    grep "seven" test.txt -c    #-c: count the number of lines(not words) that contain "seven"

    #Match everything.
    grep ".*" test.txt --color
    #-w: word.Match the word.
    grep -w "seven" test.txt --color

    #<seven: words begin with "seven"
    grep "<seven" test.txt --color
    grep "seven>" test.txt --color

    #^seven: lines(not words) begin with "seven"
    grep "^seven" test.txt --color
    grep "seven$" test.txt --color

    #-C num: print num lines around the matched line.
    grep -C 1 "twentyseven" test.txt --color
    #-A num: print num lines after the matched line.
    grep -A 1 "twentyseven" test.txt --color
    #-B num: print num lines before the matched line.
    grep -B 1 "twentyseven" test.txt --color

    #-E: extended-regexp.    -E is essential here. The 2nd method is better.
    grep -E "[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}" /etc/resolv.conf  --color
    grep -E "[0-9]{1,3}(.[0-9]{1,3}){3}" /etc/resolv.conf  --color

    #-v: invert-match. Print the non-matching lines.
    grep -E "[0-9]{1,3}(.[0-9]{1,3}){3}" /etc/resolv.conf | grep -v "#" --color
    #-o: only-matching. Print only the matched parts, with each part on a single line.
    grep -oE "[0-9]{1,3}(.[0-9]{1,3}){3}" /etc/resolv.conf --color

    #|: or.
    vmstat|grep -E "procs|swpd" --color

    #[:upper:] upper alphabets. [:digit:] numbers 0-9.
    grep "[[:upper:]]" test.txt    --color
    grep "[[:digit:]]" test.txt --color

    #Find the lines that contains six/seven/eight more than once.
    #NOTE:parenthesis is essential here. Otherwise, what do you think of "1"?
    grep -E "(six|seven|eight).*1" test.txt --color

    #-r:recursive    -i:ignore-case    -n:line number
    grep -rin "lxw" /home/lxw/Documents/ShellScript/grepDemo.sh --color
}

main

其中test.txt的内容如下:

one two three
seven eight one eight three
thirteen fourteen fifteen
 sixteen seventeen eighteen seven
sixteen seventeen eighteen
        twenty seven
one 504 one
one 503 one
one     504     one
one     504 one
#comment UP
twentyseven
        #comment down
twenty1
twenty3
twenty5
twenty7

Reference:

grep是什么？怎么用？http://blog.jobbole.com/75410/#comment-61666