grep

grep家族
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grep:   在文件中全局查找指定的正则表达式，并打印所有包含该表达式的行
egrep:  扩展的egrep，支持更多的正则表达式元字符
fgrep:  固定grep(fixed grep)，有时也被称作快速(fast grep)，它按字面解释所有的字符


一、grep命令格式
grep [选项] PATTERN filename filename ...
# grep 'Tom' /etc/passwd
# grep 'bash shell' /etc/test   
找到：                     grep返回的退出状态为0
没找到：                    grep返回的退出状态为1
找不到指定文件：    grep返回的退出状态为2

grep 程序的输入可以来自标准输入或管道，而不仅仅是文件，例如：
# grep 'tom'
# ps aux |grep 'sshd'
# ll |grep '^d'
# grep 'alice' /etc/passwd /etc/shadow /etc/group


二、grep使用的元字符
grep:                       使用基本元字符集    ^, $, ., *, [], [^], \< \>,\(\),\{\}
egrep(或grep -E):    使用扩展元字符集    ?, +, { }, |, ( )
注：grep也可以使用扩展集中的元字符，仅需要对这些元字符前置一个反斜线

\w                      所有字母与数字，称为字符[a-zA-Z0-9]         'l[a-zA-Z0-9]*ve'           'l\w*ve'
\W                      所有字母与数字之外的字符，称为非字符      'love[^a-zA-Z0-9]+'         'love\W+'
\b                          词边界                                                             '\<love\>'                      '\blove\b'                      


三、grep 示例
grep -E 或 egrep
# egrep 'NW' datafile   
# egrep 'NW' d*     
# egrep '^n' datafile
# egrep '4$' datafile
# egrep TB Savage datafile
# egrep 'TB Savage' datafile
# egrep '5\..' datafile 
# egrep '\.5' datafile      
# egrep '^[we]' datafile
# egrep '[^0-9]' datafile   
# egrep '[A-Z][A-Z] [A-Z]' datafile
# egrep 'ss* ' datafile     
# egrep '[a-z]{9}' datafile
# egrep '\<north' datafile
# egrep '\<north\>' datafile    
# egrep '\<[a-r].*n\>' datafile
# egrep '^n\w*\W' datafile  
# egrep '\bnorth\b' datafile

# egrep 'NW|EA' datafile
# egrep '3+' datafile
# egrep '2\.?[0-9]' datafile    
# egrep '(no)+' datafile
# egrep 'S(h|u)' datafile
# egrep 'Sh|u' datafile


三、grep选项
-i, --ignore-case                   忽略大小写
-l, --files-with-matches        只列出匹配行所在的文件名
-n, --line-number               在每一行前面加上它在文件中的相对行号
-c, --count                         显示成功匹配的行数
-s, --no-messages               禁止显示文件不存在或文件不可读的错误信息
-q, --quiet, --silent               静默--quiet, --silent
-v, --invert-match              反向查找，只显示不匹配的行
-R, -r, --recursive             递归针对目录
--color                             颜色
-o, --only-matching         只显示匹配的内容
-B, --before-context=NUM  print NUM lines of leading context
-A, --after-context=NUM      print NUM lines of trailing context
-C, --context=NUM            print NUM lines of output context


示例：
[[email protected] ~]# egrep 'ifcfg' /etc/*          文件
[[email protected] ~]# grep -R 'ifcfg' /etc           目录

[[email protected] ~]# egrep 'root' /etc/passwd /etc/shadow /etc/hosts
/etc/passwd:root:x:0:0:root:/root:/bin/bash
/etc/passwd:operator:x:11:0:operator:/root:/sbin/nologin
/etc/shadow:root:$6$gcO6Vp4t$OX9LmVgpjtur67UQdUYfw7vJW.78.uRXCLIxw4mBk82Z99:7:::

[[email protected] ~]# egrep -l 'root' /etc/passwd /etc/shadow /etc/hosts
/etc/passwd
/etc/shadow

[[email protected] ~]# egrep -n 'root' /etc/passwd /etc/shadow /etc/hosts 
/etc/passwd:1:root:x:0:0:root:/root:/bin/bash
/etc/passwd:11:operator:x:11:0:operator:/root:/sbin/nologin
/etc/shadow:1:root:$6$gcO6Vp4t$OX9LmVgpjtur67UQdUy8.M78.uRXCLIxw4mBk82ZrNlxyf54

[[email protected] ~]# egrep '54:04:A6:CE:C2:1F' /etc/sysconfig/*

[[email protected] ~]# egrep -R '54:04:A6:CE:C2:1F' /etc/sysconfig/

[[email protected] ~]# egrep '^IPADDR' /etc/sysconfig/network-scripts/ifcfg-eth0 |egrep -o '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
192.168.2.254
[[email protected] ~]# egrep '^IPADDR' /etc/sysconfig/network-scripts/ifcfg-eth0 |egrep -o '([0-9]{1,3}\.){3}[0-9]{1,3}'
192.168.2.254

[[email protected] ~]# grep --help |grep '\-R'
  -R, -r, --recursive       equivalent to --directories=recurse
  
[[email protected] ~]# grep --help |egrep -A5 '\-R'
  -R, -r, --recursive       equivalent to --directories=recurse
      --include=FILE_PATTERN  search only files that match FILE_PATTERN
      --exclude=FILE_PATTERN  skip files and directories matching FILE_PATTERN
      --exclude-from=FILE   skip files matching any file pattern from FILE
      --exclude-dir=PATTERN  directories that match PATTERN will be skipped.
  -L, --files-without-match  print only names of FILEs containing no match


作业：
判断输入的是否是合法的IP的地址
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[[email protected] ~]# cat /etc/passwd |grep -E '^(root|alice)'
root:x:0:0:root:/root:/bin/bash
alice:x:1000:1000:alice:/home/alice:/bin/bash
[[email protected] ~]# cat /etc/passwd |grep '^(root|alice)'
root:x:0:0:root:/root:/bin/bash
alice:x:1000:1000:alice:/home/alice:/bin/bash