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 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 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 if any line was selected, otherwise;
if any error occurs and -q was not given, the exit status is .
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
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\nhelo\n 4 5" | grep -c "[0-9]"
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\nhelo\n 4 5" | grep "[0-9]" | wc -w
8.-n参数，打印关键词所在行数
amosli@amosli-pc:~/learn/grep$ grep -n 'hi' test.txt
:hi,amos
: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::this is linux world
test2.txt::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::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::hi,amos
./test2.txt::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\n2\n3\n4\n5\n6\n7\n8\n9\n10" | grep ''
-A,打印出关键词之后的５行,after
amosli@amosli-pc:~/learn/grep$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | grep '' -A
-B,打印出关键词之前的２行，before
amosli@amosli-pc:~/learn/grep$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | grep '' -B
-C,打印出关键词前后2行
amosli@amosli-pc:~/learn/grep$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | grep '' -C
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$ $?
: command not found
找到关键词：
amosli@amosli-pc:~/learn/grep$ grep -q 'amos' test.txt
amosli@amosli-pc:~/learn/grep$ $?
: 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'