grep(global search regular expression(RE) and print out the line,全面搜索正則表達式並把行打印出來)是unix/linux中用於文本搜索的大師級的工具。它能夠接受正則表達式和通配符。
首先，輸入grep --help查看幫助信息:
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.
語法格式：
grep [OPTIONS] PATTERN [FILE...] grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]
參數-實例：
test.txt
amosli@amosli-pc:~/learn/grep$ cat test.txt hi,amos this is linux world grep command is powerful!
1.在文件中搜索一個單詞
iamosli@amosli-pc:~/learn/grep$ grep 'hi' test.txt hi,amos this is linux world
2.從標准輸入中搜索一個單詞
amosli@amosli-pc:~/learn/grep$ echo this is a word | grep hi this is a word
也可以加上參數-e，表示根據模式進行匹配,下面部分也將會對-e參數進行介紹
amosli@amosli-pc:~/learn/grep$ echo this is a word | grep -e hi this is a word
3.-E參數,使用正則表達式進行搜索關鍵字
amosli@amosli-pc:~/learn/grep$ echo this is a word | grep -E [a-z]+d this is a word
-E參數英文提示信息:
-E, --extended-regexp PATTERN is an extended regular expression (ERE)
意思是使用擴展(extended)的正則表達式.在文章開始的提示信息中有這么一段"egrep' means `grep -E'. ",所以也可以直接使用egrep命令進行搜索
amosli@amosli-pc:~/learn/grep$ echo this is a word | egrep "[a-z]+d" this is a word
4.-o參數，只輸出匹配到的文本部分，沒有匹配到的不顯示
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參數，重點標記出匹配到的文本
amosli@amosli-pc:~/learn/grep$ echo this a line. | egrep -o "[a-z]+\." --color=auto line.
除了auto之外，還可以選擇never和always，這個是表示什么時候重點標記。
英文提示信息:
--colour[=WHEN] use markers to highlight the matching strings; WHEN is `always', `never', or `auto'
6.-v參數,打印除了匹配到的文本以外的內容
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參數，統計關鍵詞出現的行數
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
這里grep只是統計出現的行數，而不是統計關鍵詞出現的次數
如：
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3\nhelo\n 4 5" | grep -c "[0-9]" 2
這里有5個數字，但只有3行，其中有兩行中出現數字，所以顯示的次數為2
如何統計文件中關鍵詞出現的次數？
可以使用wc 命令進行二次統計，如下：
amosli@amosli-pc:~/learn/grep$ echo -e "1 2 3\nhelo\n 4 5" | grep "[0-9]" | wc -w 5
8.-n參數，打印關鍵詞所在行數
amosli@amosli-pc:~/learn/grep$ grep -n 'hi' test.txt 1:hi,amos 2:this is linux world
在第1行顯示了關鍵詞所在的行，極大的方便了閱讀。
英文提示信息:
-n, --line-number print line number with output lines
--line-buffered flush output on every line
9.對多個文件進行搜索
test2.txt
amosli@amosli-pc:~/learn/grep$ cat test2.txt hi,amos this is linux world Welcome you!
對test.txt 和test2.txt進行批量查詢:
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參數，對多個文件進行搜索，但只顯示文件名
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 參數，忽略大小寫進行搜索
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參數，遞歸進行搜索
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參數，用grep匹配多個樣式,即多個條件進行查詢
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
還有一種方法可以進行樣式匹配,即把所要匹配的關鍵詞用一個文件保存起來，然后進行檢索，請看下一個參數-f
14.-f參數，用grep匹配多個樣式,即多個條件進行查詢--方法2
將關鍵詞保存到f.txt中：
amosli@amosli-pc:~/learn/grep$ cat f.txt hi linux grep
開始進行匹配:
amosli@amosli-pc:~/learn/grep$ grep -f f.txt test.txt hi,amos this is linux world grep command is powerful!
結果跟-e參數一樣，但在大文件多關鍵詞的條件下，-f參數絕對提高了查詢的效率。
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參數和--exclude參數）
amosli@amosli-pc:~/learn/grep$ cat test.html hi,amos this is linux world grep command is powerful!
開始檢索只包括.html的文件：
amosli@amosli-pc:~/learn/grep$ grep "hi,amos" . -r --include *.html -n ./test.html:1:hi,amos
開始檢索不包括.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 ,打印出關鍵詞前、后的行
amosli@amosli-pc:~/learn/grep$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | grep '3' 3
-A,打印出關鍵詞之后的５行,after
amosli@amosli-pc:~/learn/grep$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | grep '3' -A 5 3 4 5 6 7 8
-B,打印出關鍵詞之前的２行，before
amosli@amosli-pc:~/learn/grep$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | grep '3' -B 2 1 2 3
-C,打印出關鍵詞前后2行
amosli@amosli-pc:~/learn/grep$ echo -e "1\n2\n3\n4\n5\n6\n7\n8\n9\n10" | 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 參數,靜默模式輸出
在靜默模式中，grep 命令不會向標准輸出打印任何輸出，它僅是運行命令，然后根據命令執行成功與否返回退出狀態，沒有找到值則返回狀態為1,找到則返回０.
沒有找到關鍵詞：
amosli@amosli-pc:~/learn/grep$ grep -q 'abc' test.txt amosli@amosli-pc:~/learn/grep$ $? 1: command not found
找到關鍵詞：
amosli@amosli-pc:~/learn/grep$ 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'
18、其他參數,可輸入man grep查看grep命令手冊