grep(global search regular expression(RE) and print out the line,全面搜索正则表达式并把行打印出来)是unix/linux中用于文本搜索的大师级的工具。它能够接受正则表达式和通配符。
首先，输入grep --help查看帮助信息:
amosli@amosli-pc:~$ 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) -F, --fixed-strings PATTERN is a set of newline-separated fixed strings -G, --basic-regexp PATTERN is a basic regular expression (BRE) -P, --perl-regexp PATTERN is a Perl regular expression -e, --regexp=PATTERN use PATTERN for matching -f, --file=FILE obtain PATTERN from FILE -i, --ignore-case ignore case distinctions -w, --word-regexp force PATTERN to match only whole words -x, --line-regexp force PATTERN to match only whole lines -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 -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 -n, --line-number print line number with output lines --line-buffered flush output on every line -H, --with-filename print the file name for each match -h, --no-filename suppress the file name prefix on output --label=LABEL use LABEL as the standard input file name prefix -o, --only-matching show only the part of a line matching PATTERN -q, --quiet, --silent suppress all normal output --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 -l, --files-with-matches print only names of FILEs containing matches -c, --count print only a count of matching lines per FILE -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 -A, --after-context=NUM print NUM lines of trailing context -C, --context=NUM print NUM lines of output context -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. 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.
语法格式：
grep [OPTIONS] PATTERN [FILE...] grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]
参数-实例：
test.txt
amosli@amosli-pc:~/learn/grep$ cat test.txt hi,amos this is linux world grep command is powerful!
1.在文件中搜索一个单词
iamosli@amosli-pc:~/learn/grep$ grep 'hi' test.txt hi,amos this is linux world
2.从标准输入中搜索一个单词
amosli@amosli-pc:~/learn/grep$ echo this is a word | grep hi this is a word
也可以加上参数-e，表示根据模式进行匹配,下面部分也将会对-e参数进行介绍
amosli@amosli-pc:~/learn/grep$ echo this is a word | grep -e hi this is a word
3.-E参数,使用正则表达式进行搜索关键字
amosli@amosli-pc:~/learn/grep$ echo this is a word | grep -E [a-z]+d this is a word
-E参数英文提示信息:
-E, --extended-regexp PATTERN is an extended regular expression (ERE)
意思是使用扩展(extended)的正则表达式.在文章开始的提示信息中有这么一段"egrep' means `grep -E'. ",所以也可以直接使用egrep命令进行搜索
amosli@amosli-pc:~/learn/grep$ echo this is a word | egrep "[a-z]+d" this is a word
4.-o参数，只输出匹配到的文本部分，没有匹配到的不显示
amosli@amosli-pc:~/learn/grep$ echo this a line. | grep -o -E "[a-z]+." line. #或者
amosli@amosli-pc:~/learn/grep$ echo this a line. | egrep -o "[a-z]+." line.
英文提示信息:
-o, --only-matching show only the part of a line matching PATTERN
5.--color参数，重点标记出匹配到的文本
amosli@amosli-pc:~/learn/grep$ echo this a line. | egrep -o "[a-z]+." --color=auto line.
除了auto之外，还可以选择never和always，这个是表示什么时候重点标记。
英文提示信息:
--colour[=WHEN] use markers to highlight the matching strings; WHEN is `always', `never', or `auto'
6.-v参数,打印除了匹配到的文本以外的内容
常用格式：
grep -v match_pattern file
例：
amosli@amosli-pc:~/learn/grep$ grep -v 'hi,amos' test.txt this is linux world grep command is powerful!
英文提示信息:
-v, --invert-match select non-matching lines
7.-c参数，统计关键词出现的行数
amosli@amosli-pc:~/learn/grep$ grep -c hi test.txt 2
英文提示信息:
-c, --count print only a count of matching lines per FILE
这里grep只是统计出现的行数，而不是统计关键词出现的次数
如：
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3 helo 4 5" | grep -c "[0-9]" 2
这里有5个数字，但只有3行，其中有两行中出现数字，所以显示的次数为2
如何统计文件中关键词出现的次数？
可以使用wc 命令进行二次统计，如下：
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3 helo 4 5" | grep "[0-9]" | wc -w 5
8.-n参数，打印关键词所在行数
amosli@amosli-pc:~/learn/grep$ grep -n 'hi' test.txt 1:hi,amos 2:this is linux world
在第1行显示了关键词所在的行，极大的方便了阅读。
英文提示信息:
-n, --line-number print line number with output lines
--line-buffered flush output on every line
9.对多个文件进行搜索
test2.txt
amosli@amosli-pc:~/learn/grep$ cat test2.txt hi,amos this is linux world Welcome you!
对test.txt 和test2.txt进行批量查询:
amosli@amosli-pc:~/learn/grep$ grep -n 'linux' test.txt test2.txt test.txt:2:this is linux world test2.txt:2:this is linux world
10.-l参数，对多个文件进行搜索，但只显示文件名
amosli@amosli-pc:~/learn/grep$ grep -l 'linux' test.txt test2.txt test.txt test2.txt
英文提示信息:
-l, --files-with-matches print only names of FILEs containing matches
11.-i 参数，忽略大小写进行搜索
amosli@amosli-pc:~/learn/grep$ echo "THIS IS test" | grep -i "th" THIS IS test
英文提示信息:
-i, --ignore-case ignore case distinctions
12.-R参数，递归进行搜索
amosli@amosli-pc:~/learn/grep$ cd .. amosli@amosli-pc:~/learn$ grep 'hi,amos' . -R ./grep/test.txt:hi,amos ./grep/test2.txt:hi,amos
英文提示信息:
-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.
13.-e参数，用grep匹配多个样式,即多个条件进行查询
amosli@amosli-pc:~/learn/grep$ grep -e "hi" -e "linux" -e "grep" test.txt hi,amos this is linux world grep command is powerful!
英文提示信息：
-e, --regexp=PATTERN use PATTERN for matching
还有一种方法可以进行样式匹配,即把所要匹配的关键词用一个文件保存起来，然后进行检索，请看下一个参数-f
14.-f参数，用grep匹配多个样式,即多个条件进行查询--方法2
将关键词保存到f.txt中：
amosli@amosli-pc:~/learn/grep$ cat f.txt hi linux grep
开始进行匹配:
amosli@amosli-pc:~/learn/grep$ grep -f f.txt test.txt hi,amos this is linux world grep command is powerful!
结果跟-e参数一样，但在大文件多关键词的条件下，-f参数绝对提高了查询的效率。
英文提示信息：
-f, --file=FILE obtain PATTERN from FILE
15.在grep搜索中包括或排除指定的文件（--include参数和--exclude参数）
amosli@amosli-pc:~/learn/grep$ cat test.html hi,amos this is linux world grep command is powerful!
开始检索只包括.html的文件：
amosli@amosli-pc:~/learn/grep$ grep "hi,amos" . -r --include *.html -n ./test.html:1:hi,amos
开始检索不包括.html的文件：
amosli@amosli-pc:~/learn/grep$ grep "hi,amos" . -r --exclude *.html -n ./test.txt:1:hi,amos ./test2.txt:1:hi,amos
英文提示信息：
-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.
16.-A,-B,-C ,打印出关键词前、后的行
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3 4 5 6 7 8 9 10" | grep '3' 3
-A,打印出关键词之后的５行,after
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3 4 5 6 7 8 9 10" | grep '3' -A 5 3 4 5 6 7 8
-B,打印出关键词之前的２行，before
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3 4 5 6 7 8 9 10" | grep '3' -B 2 1 2 3
-C,打印出关键词前后2行
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3 4 5 6 7 8 9 10" | grep '3' -C 2 1 2 3 4 5
英文提示信息：
-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
17.-q 参数,静默模式输出
在静默模式中，grep 命令不会向标准输出打印任何输出，它仅是运行命令，然后根据命令执行成功与否返回退出状态，没有找到值则返回状态为1,找到则返回０.
没有找到关键词：
amosli@amosli-pc:~/learn/grep$ grep -q 'abc' test.txt amosli@amosli-pc:~/learn/grep$ $? 1: command not found
找到关键词：
amosli@amosli-pc:~/learn/grep$ grep -q 'amos' test.txt amosli@amosli-pc:~/learn/grep$ $? 0: command not found
英文提示信息：
-q, --quiet, --silent suppress all normal output --binary-files=TYPE assume that binary files are TYPE; TYPE is `binary', `text', or `without-match'