Linux-三剑客之grep

一、grep

1、描述

　　grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints the matching lines.(个人理解:使用指定模式从文件中筛选中匹配的信息)

2、grep增强命令

　　egrep：等同于grep -E

3、使用规则

# grep 参数  匹配模式    文件
grep [OPTIONS] PATTERN [FILE...]

4、参数详解

1. -V 打印grep版本信息；

    -V, --version
        Print the version number of grep to the standard output stream.  This version number should be included in all bug reports (see below).

   代码示例：

   [root@doctor-10 ~]# grep -V
   grep (GNU grep) 2.20
   Copyright (C) 2014 Free Software Foundation, Inc.
   License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
   This is free software: you are free to change and redistribute it.
   There is NO WARRANTY, to the extent permitted by law.
   Written by Mike Haertel and others, see <http://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>

2. -E 使用扩展正则表达式；

   常见的扩展规则符号：+ ? ^ $ | （） { }

    -E, --extended-regexp
        Interpret PATTERN as an extended regular expression (ERE, see below).  (-E is specified by POSIX.)

   代码案例：

   #筛选出/etc/passwd中的普通用户
   [root@doctor-10 /etc]# grep 'bash' /etc/passwd
   root:x:0:0:root:/root:/bin/bash
   hadoop:x:1000:1000::/home/hadoop:/bin/bash
   [root@doctor-10 /etc]# grep 'bash+' /etc/passwd  #无法识别扩展正则符号(错误写法)
   [root@doctor-10 /etc]# grep -E 'bash+' /etc/passwd #(正确)
   root:x:0:0:root:/root:/bin/bash
   hadoop:x:1000:1000::/home/hadoop:/bin/bash

3. -e 可以指定多个匹配模式

   -e PATTERN, --regexp=PATTERN
       Use PATTERN as the pattern.  This can be used to specify multiple search patterns, or to protect a pattern beginning with a hyphen (-).  (-e is specified by POSIX.)

   代码案例：

4. -v 打印出不满足匹配模式的行

   -v, --invert-match
          Invert the sense of matching, to select non-matching lines.  (-v is specified by POSIX.)

   代码案例：

   

5. -c 统计出满足匹配模式的个数；

    -c, --count
             Suppress normal output; instead print a count of matching lines for each input file.  With the -v, --invert-match option (see below), count non-matching lines.  (-c  is
              specified by POSIX.)

   代码案例：

   

6. -n 显示满足匹配模式的行号

    -n, --line-number
          Prefix each line of output with the 1-based line number within its input file.  (-n is specified by POSIX.)

   代码案例：

   

7. -A 打印出满足匹配模式的后# 行（# 指定要显示的行数）

   -A NUM, --after-context=NUM
        Print  NUM  lines of trailing context after matching lines.  Places a line containing a group separator (described under --group-separator) between contiguous groups of matches.  With the -o or --only-matching option, this has no effect and a warning is given.　　

   代码案例：

   

8. -B 显示满足匹配模式的前#行（# 指定要显示的行数）

   -B NUM, --before-context=NUM
       Print NUM lines of leading context before matching lines.  Places a line containing a group separator (described under --group-separator) between contiguous  groups  of matches.  With the -o or --only-matching option, this has no effect and a warning is given.　　

   代码案例：

   

9. -C 显示满足匹配模式的前后 #行（# 指定要显示的行数）

    -C NUM, -NUM, --context=NUM
       Print NUM lines of output context.  Places a line containing a group separator (described under --group-separator) between contiguous groups of matches.  With the -o or --only-matching option, this has no effect and a warning is given.

   代码案例：