grep --help
[root@ora ~]# grep --help
Usage: grep [OPTION]... PATTERN [FILE]...
Search for PATTERN in each FILE or standard input.
PATTERN is, by default, a basic regular expression (BRE).
Example: grep -i 'hello world' menu.h main.c
Regexp selection and interpretation:
-E, --extended-regexp PATTERN is an extended regular expression (ERE) 模式是一个扩展正则表达式
-F, --fixed-strings PATTERN is a set of newline-separated fixed strings PATTERN是一组以新行分隔的固定字符串
-G, --basic-regexp PATTERN is a basic regular expression (BRE) 模式是一个基本的正则表达式(BRE)
-P, --perl-regexp PATTERN is a Perl regular expression PATTERN是一个Perl正则表达式
-e, --regexp=PATTERN use PATTERN for matching 使用模式进行匹配
-f, --file=FILE obtain PATTERN from FILE 从文件中获取模式
-i, --ignore-case ignore case distinctions 忽略大小写的区别
-w, --word-regexp force PATTERN to match only whole words 强制pattern只匹配整个单词，精确匹配整个单词
-x, --line-regexp force PATTERN to match only whole lines 强制pattern只匹配整行，精确匹配整行
-z, --null-data a data line ends in 0 byte, not newline
Miscellaneous:
-s, --no-messages suppress error messages
-v, --invert-match select non-matching lines 反相匹配
-V, --version print version information and exit
--help display this help and exit
--mmap ignored for backwards compatibility
Output control:
-m, --max-count=NUM stop after NUM matches
-b, --byte-offset print the byte offset with output lines 额外打印字节偏移量
-n, --line-number print line number with output lines 额外打印行号
--line-buffered flush output on every line
-H, --with-filename print the filename for each match
-h, --no-filename suppress the prefixing filename on output
--label=LABEL print LABEL as filename for standard input
-o, --only-matching show only the part of a line matching PATTERN 只显示匹配的部分
-q, --quiet, --silent suppress all normal output 安静模式，不输出
--binary-files=TYPE assume that binary files are TYPE;
TYPE is `binary', `text', or `without-match'
-a, --text equivalent to --binary-files=text
-I equivalent to --binary-files=without-match
-d, --directories=ACTION how to handle directories;
ACTION is `read', `recurse', or `skip'
-D, --devices=ACTION how to handle devices, FIFOs and sockets;
ACTION is `read' or `skip'
-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 打印不能匹配的文件名
-l, --files-with-matches print only names of FILEs containing matches 打印能匹配上的文件名
-c, --count print only a count of matching lines per FILE 打印匹配的行数
-T, --initial-tab make tabs line up (if needed)
-Z, --null print 0 byte after FILE name
Context control:
-B, --before-context=NUM print NUM lines of leading context 附加打印后几行
-A, --after-context=NUM print NUM lines of trailing context 附加打印前几行
-C, --context=NUM print NUM lines of output context 附加打印前后几行
-NUM same as --context=NUM
--color[=WHEN],
--colour[=WHEN] use markers to highlight the matching strings;
WHEN is `always', `never', or `auto'
-U, --binary do not strip CR characters at EOL (MSDOS)
-u, --unix-byte-offsets report offsets as if CRs were not there (MSDOS)
`egrep' means `grep -E'. `fgrep' means `grep -F'.
Direct invocation as either `egrep' or `fgrep' is deprecated. 直接调用egrep和fgrep已经废弃了，使用grep –e /-f
With no FILE, or when FILE is -, read standard input. If less than two FILEs
are given, assume -h. Exit status is 0 if any line was selected, 1 otherwise;
if any error occurs and -q was not given, the exit status is 2.
匹配得上返回0，匹配不上返回1，有错误返回2
示例
准备材料
[root@node0 tmp]# cat passwd
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
10 uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
-i 忽略大小写
[root@node0 tmp]# cat passwd |grep -i ROOT
1 root:x:0:0:root:/root:/bin/bash
-w 精确匹配
[root@node0 tmp]# cat passwd |grep roo
1 root:x:0:0:root:/root:/bin/bash
[root@node0 tmp]# cat passwd |grep -w roo
-x 匹配整行
[root@node0 tmp]# cat passwd |grep roo
1 root:x:0:0:root:/root:/bin/bash
[root@node0 tmp]# cat passwd |grep -x roo
-v 反向匹配
[root@node0 tmp]# cat passwd |grep roo
1 root:x:0:0:root:/root:/bin/bash
[root@node0 tmp]# cat passwd |grep -v roo
2 bin:x:1:1:bin:/bin:/sbin/nologin
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
10 uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
-n 显示行号
[root@node0 tmp]# cat passwd |grep -v -n roo
2:2 bin:x:1:1:bin:/bin:/sbin/nologin
3:3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4:4 adm:x:3:4:adm:/var/adm:/sbin/nologin
5:5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6:6 sync:x:5:0:sync:/sbin:/bin/sync
7:7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8:8 halt:x:7:0:halt:/sbin:/sbin/halt
9:9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
10:10 uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
11:9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
-c 匹配的行的数量
[root@node0 tmp]# cat passwd |grep -c mail
2
-B 附加打印前几行
root@node0 tmp]# cat passwd |grep -B 4 shutdown
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
-A 附加打印后几行
[root@node0 tmp]# cat passwd |grep -A 2 shutdown
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
-C 附加打印前后几行
[root@node0 tmp]# cat passwd |grep -C 2 shutdown
5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
去除文件中的空白行
cat passwd |grep –v '^$'
去除文件中的注释行
cat passed |grep –v '^#'
[root@node0 tmp]# cat passwd
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
#5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
10 uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
[root@node0 tmp]# cat passwd |grep -v '^$'
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
#5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
10 uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
[root@node0 tmp]# cat passwd |grep -v '^$'|grep -v '^#'
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
10 uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
[root@node0 tmp]#