Linux命令详解之 grep

linux 命令详解

本文主要内容来自Linux man 手册

命令名称：

grep（global search regular express and print out line）打印匹配的行（内容） 类似的命令包括egrep、fgrep、rgrep 

命令用法：

grep [选项] 匹配项[PATTERN...] []表示可选参数 grep [选项[ [-e 匹配项]... [-f PATTERN]... [FILE...] PATTERN为正则表达式 

命令概述：

grep在指定的文件中搜索包含PATTERN匹配的行。如果不指定文件或指定了“-”，则从标准输入中进行搜 索。 默认情况下，grep打印匹配的行。 此外，grep还有很多演变命令，如egrep、fgrep和rgpre，分别对应grep -E、grep -F和grep -r。 这些变种已经弃用，但他们被提供用作向后兼容。 

命令参数：

-E, --extended-regexp 将PATTERN作为扩展的正则表达式（ERE) -F，--fixed-strings 将PATTERN作为为固定字符串的列表，由换行符分隔，匹配其中任意一个 -G, --basic-regexp 将PATTERN作为基本正则表达式（BRE），该选项为默认设置 -P，--perl-regexp 将PATTERN作为perl兼容正则表达式（PCRE)。 

2.匹配控制

-e PATTERN, --regexp=PATTERN 将PATTERN作为匹配项，如果该选项被多次使用或和-f（--file）选项一起使用，匹配所有 的匹配项。该选项可以用来保护以'-'开头的匹配项。 -f FILE，--file=FILE 将FILE中的每行都作为匹配项，如果此选项被多次使用或与-e（--regexp）选项组合使用，搜索所有 给定的匹配项。空文件包含零个匹配项，因此不匹配任何内容 -i，--ignore-case 忽略匹配项的大小写 -v，--invert-match 反向匹配，选择没有匹配上的行 -w，--word-regexp 仅匹配完整单词，匹配的子字符串必须位于行的开头，或者前面有一个非字词字符。类似地，它必须位于 行尾或后面跟非字词组成字符（字词组成字符是字母、数字和下划线）。 -x，--line-regexp 仅选择与整行完全匹配的匹配项。对于正则表达式匹配项，这类似于将匹配项括起来，然后用^和$将其 包围。 -y 和-i作用相同，但已过时 

3.通用输出控制

-c，--count 不打印匹配结果，而是打印匹配的行数 --color[=WHEN]，--colour[=WHEN] 将匹配到的字符串、行、上下文行、文件名、行号、字节偏移量和带转义符的分隔符（用于字段和上下文 行组）序列着色，颜色有环境变量GREP_COLORS决定，虽然GREP_COLOR已经过时，但grep依然支持该 环境变量，只不过优先权比GREP_COLORS低。WHEN可以为never、always和auto。相关环境变量介绍 ：略。 -L，--files-without-match 不打印正常匹配结果，而是打印没有匹配上的文件的名称，扫描将在第一次匹配时停止。 -l，--files-with-matches 不打印正常匹配结果，而是打印匹配上的输入文件的名称，扫描将在第一次匹配时停止 -m NUM --max-count=NUM 在匹配到NUM行后停止读取文件 -o，--only-matching 仅打印匹配行中（非空的）匹配部分，每个部分在单独的输出行上 -q，--quiet，--silent 不向标准输出打印任何内容，匹配到内容立刻退出，即使检测到错误 -s，--no-messages 当文件不存在或文件不可读取时，不显示错误信息 

4.输出行前缀控制

-b，--byte-offset 在每行输出之前，打印输入文件中基于0的字节偏移量。如果指定了-o（--only-matching），则打印 匹配项本身的偏移量 -H，--with-filename 打印每个匹配的文件名，当匹配到多个匹配项时，该选项为默认配置 -h，--no-filename 在输出中不显示文件名，只匹配到单个结果时，默认不显示文件名 --label=LABEL 将标准输入显示为来自文件标签的输入（？？？不理解） -n，--line-number 显示行号 -T，--initial-tab 使匹配结果中每行的第一个字符位于制表位上，以便制表的对齐看起来显得正常。该选项对一些给输出内 容加前缀的选项很有作用：-H、-n和-b -u，--unix-byt-offsets 报告Unix样式的字节偏移量，此开关使grep报告字节偏移量，就像文件是Unix样式的文本文件一样，即 去掉CR字符。这将产生与在Unix机器上运行grep相同的结果。除非同时使用-b选项，否则此选项无效， 它对MS-DOS和MS Windows以外的平台没有影响。 -Z，--null 将文件名后面的符号（冒号或回车）改为零字节（ASCII NUL 字符），例如，grep -lZ在每个文件名 后输出一个零字节，而不是通常的换行。此选项使输出明确，甚至如果文件名包含不寻常的字符，如新行。 此选项可与其他命令一起使用，如find -print0、perl-0、sort-z和xargs-0来处理任意文件名， 甚至包含换行符的文件名。 

5.上下文行控制

-A NUM，--after-context=NUM 在匹配行之后打印下文的NUM行,连续的匹配组之间用分隔符“--”隔开。和-o或--only-matching选项 一起使用时，该选项没有任何效果，并且会发出警告 -B NUM，--before-context=NUM 在匹配行的前面打印上文的NUM行，,连续的匹配组之间用分隔符“--”隔开。和-o或--only-matching 选项一起使用时，该选项没有任何效果，并且会发出警告 -C NUM，-NUM，--context=NUM 打印匹配行的上下文各NUM行，连续的匹配组之间用分隔符“--”隔开。和-o或--only-matching选项 一起使用时，该选项没有任何效果，并且会发出警告 

6.文件及目录的选择

-a，--text 像处理文本一样处理二进制文件，相当于--binary-files=text选项 --binary-files=TYPE 如果文件的前几个字节指示该文件包含二进制数据，则假定文件的类型为TYEP。默认情况下，TYPE为 binary，grep通常只输出一行表示二进制文件匹配的消息，或者因为没有匹配结果而没有输出；如果 TYPE为without-match，则grep不对二进制文件进行匹配，相当于-I选项；如果TYPE为text，grep 将二进制文件当作文本文件处理，这相当于-a选项，处理二进制数据时，grep可以将非文本字节视为行 终止符，例如，模式“.”（句点）可能不能匹配空字节，因为空字节可能被视为行终止符。警告：grep --binary-files=text可能输出二进制垃圾，如果输出是终端且终端驱动程序将其中一些文本解释为 命令则可能会产生严重的副作用。 -D ACTION，--devices=ACTION 如果输入文件是一个设备、FIFO或则套接字，使用ACTION去处理它，ACTION默认为read，意味着该文 件将被当作普通文件进行读取。如果ACTION为skip，设备文件被忽略。 -d ACTION，--directories=ACTION 如果输入文件为一个目录，使用ACTION处理它。ACTION默认为read，即将目录作为普通文件处理。如果 ACTION为skip，跳过该目录。如果ACTION为recurse，递归读取目录下的所有文件，并且遵循命令行 符号链接，相当于-r选项 --exclude=GLOB 跳过名称与GLOB匹配的文件（使用通配符匹配），文件名glob可以使用*、？、和[…]作为通配符，并逐 字引用通配符或反斜杠字符。 --exclude-from=FILE 跳过其基名称与从FILE读取的任意文件名通过glob匹配的文件（使用通配符匹配，如--exclude下所述） --exclude-dir=DIR 从递归搜索中排除与DIR匹配的目录 -I 处理二进制文件，就像它不包含匹配的数据一样，这相当于--binary-files=without-match选项。 --include=GLOB 搜索名称与从GLOB匹配的文件（使用通配符匹配，如--exclude下所述） -r，--recursive 递归读取目录下的所有文件，并且遵循命令行符号链接。如果没有给定文件操作数，grep将搜索当前工作 目录。该命令相当于-d recurse选项 -R，--dereference-recursive 递归读取目录下所有文件，遵循所有符号链接 

7.其他选项

--line-buffered 在输出上使用行缓冲，这可能会导致性能下降 -U，--binary 将文件视为二进制文件，默认情况下，在MS-DOS和MS-Window中，grep通过读取文件前32KB的内容决 定这个文件的类型，如果文件为文本文件，grep从原始文件中删除CR字符（使带有‘^'和’$'的正则表达 式能正常工作），指定-U可以让其对文件进行逐字读取。如果文件为文本文件，每行末尾有CR/LF，这将 造成一些正则表达式失效。该选项对MS-DOS和MS-Windows以外的平台无影响。 -z，--null-data 将输入视为一组行，每个行以零字节（ASCII NUL字符）而不是换行符终止，与-Z或--null选项类似， 此选项可以与sort -z等命令一起使用，以处理任意文件名。 

8.通用信息

--help 显示帮助信息 --version 显示版本信息 

示例：

1. grep PATTERN…

grep的第一种用法 ，不带任何参数，根据匹配项PATTERN进行匹配。

xiaohui@ubuntu:~/work/grep_learn$ ls | grep .c grep_test_2.c grep_test_3.c grep_test.c xiaohui@ubuntu:~/work/grep_learn$ 

2. grep PATTERN… FILE…

grep的第二种用法 ，不带任何参数，根据匹配项进行匹配。

xiaohui@ubuntu:~/work/grep_learn$ cat grep_test.c iigrep.... learn text xiaohui@ubuntu:~/work/grep_learn$ grep text ./grep_test.c text xiaohui@ubuntu:~/work/grep_learn$ 

3. grep -E/-G PATTERN… [FILE…]

由于在grep中，基本正则表达式和扩展正则表达式在使用时的区别在于：在基本正则表达式中，元字符？、+、{、|、(、和)失去了特殊意义，需要使用反斜杠版本\？、+、{、|、(、和\）。如果不加任何匹配方式的选项，默认为-G，即基本正则表达式。

xiaohui@ubuntu:~/work/grep_learn$ cat grep_test_2.c apple banana cat dog egg fire glof 12 34 56 78 90 xiaohui@ubuntu:~/work/grep_learn$ grep -G [a-g] grep_test_2.c apple banana cat dog egg fire glof xiaohui@ubuntu:~/work/grep_learn$ grep -G [1-9] grep_test_2.c 12 34 56 78 90 xiaohui@ubuntu:~/work/grep_learn$ 

4. grep -F PATTERN… [FILE…]

将PATTERN作为固定字符串形式的匹配项，不识别正则表达式。

xiaohui@ubuntu:~/work/grep_learn$ cat grep_test.c ^abc abc efg$ efg text* textxx headxxxxend headaaaaend head*end xiaohui@ubuntu:~/work/grep_learn$ grep ^abc grep_test.c abc xiaohui@ubuntu:~/work/grep_learn$ grep -F ^abc grep_test.c ^abc xiaohui@ubuntu:~/work/grep_learn$ grep efg$ grep_test.c efg xiaohui@ubuntu:~/work/grep_learn$ grep -F efg$ grep_test.c efg$ xiaohui@ubuntu:~/work/grep_learn$ grep text* grep_test.c text* textxx xiaohui@ubuntu:~/work/grep_learn$ grep -F text* grep_test.c text* xiaohui@ubuntu:~/work/grep_learn$ 

5. grep -e PATTERN… [FILE…] 和grep -f FILE… [FILE…]

-e的作用和不加参数时类似，唯一区别是可以保护以‘-’开头的匹配项

xiaohui@ubuntu:~/work/grep_learn$ grep -e -* grep_test.c ^abc abc efg$ efg text* textxx headxxxxend headaaaaend head*end -test //-符号标红 test xiaohui@ubuntu:~/work/grep_learn$ grep -test grep_test.c grep: invalid option -- 't' Usage: grep [OPTION]... PATTERN [FILE]... Try 'grep --help' for more information. xiaohui@ubuntu:~/work/grep_learn$ grep -e -test grep_test.c -test xiaohui@ubuntu:~/work/grep_learn$ 

-e选项可以多次使用，匹配更多的内容

xiaohui@ubuntu:~/work/grep_learn$ grep -e -test -e test grep_test.c -test test xiaohui@ubuntu:~/work/grep_learn$ 

-f的作用是将FILE中的每行都作为匹配项，和-e一样可以多次使用

xiaohui@ubuntu:~/work/grep_learn$ grep -f grep_file.c grep_*.c grep_file.c:test grep_file.c:text grep_file.c:head grep_file.c:end grep_test_2.c:text_2 grep_test_2.c:test_2 grep_test_3.c:text_3 grep_test_3.c:test_3 grep_test.c:text* grep_test.c:textxx grep_test.c:headxxxxend grep_test.c:headaaaaend grep_test.c:head*end grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ cat grep_file.c test text head end xiaohui@ubuntu:~/work/grep_learn$ echo [a-b] > grep_file_2.c xiaohui@ubuntu:~/work/grep_learn$ grep -f grep_file_2.c -f grep_file.c grep_*.c grep_file_2.c:[a-b] grep_file.c:test grep_file.c:text grep_file.c:head grep_file.c:end grep_test_2.c:apple grep_test_2.c:banana grep_test_2.c:cat grep_test_2.c:text_2 grep_test_2.c:test_2 grep_test_3.c:text_3 grep_test_3.c:test_3 grep_test.c:^abc grep_test.c:abc grep_test.c:text* grep_test.c:textxx grep_test.c:headxxxxend grep_test.c:headaaaaend grep_test.c:head*end grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ 

-e和-f也可以同时使用，匹配所有匹配项。

xiaohui@ubuntu:~/work/grep_learn$ grep -f grep_file.c -e test grep_test.c text* textxx headxxxxend headaaaaend head*end -test test xiaohui@ubuntu:~/work/grep_learn$ cat grep_file.c test text head end xiaohui@ubuntu:~/work/grep_learn$ 

6. grep -i PATTERN… [FILE…]

忽略匹配项PATTERN的大小写

xiaohui@ubuntu:~/work/grep_learn$ grep -i test grep_test.c TEST -test test xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test.c -test test xiaohui@ubuntu:~/work/grep_learn$ 

7. grep -v PATTERN… [FILE…]

反向匹配

xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test.c -test test xiaohui@ubuntu:~/work/grep_learn$ grep -v test grep_test.c ^abc abc efg$ efg text* textxx TEXT TEST xiaohui@ubuntu:~/work/grep_learn$ 

8. grep -w PATTERN… [FILE…]

匹配完整的单词，单词前后不能有其他字母或数字，但允许单词前面有非字词符号。

xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test_3.c xxtest testxx _test -test test_3 test test_ xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ grep -w test grep_test_3.c -test test xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ 

9. grep -x PATTERN… [FILE…]

整行匹配

xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test_3.c xxtest testxx _test -test test_3 test test_ xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ grep "This is a test file" grep_test_3.c This is a test file. xiaohui@ubuntu:~/work/grep_learn$ 

10. grep -c PATTERN… [FILE…]

打印匹配的行数（不是行号），而不打印匹配内容

xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test_3.c xxtest testxx _test -test test_3 test test test test_ xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ grep test -c grep_test_3.c 9 xiaohui@ubuntu:~/work/grep_learn$ 

11. grep -color[=WHEN] PATTERN… [FILE…]

12. grep -L PATTERN… [FILE…]

不打印匹配的内容，打印FILE中没有匹配上的文件

xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_*.c grep_file.c:test grep_test_2.c:test_2 grep_test_3.c:xxtest grep_test_3.c:testxx grep_test_3.c:_test grep_test_3.c:-test grep_test_3.c:test_3 grep_test_3.c:test test test grep_test_3.c:test_ grep_test_3.c:xxx xxx test- grep_test_3.c:This is a test file. grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_*.c -L grep_file_2.c xiaohui@ubuntu:~/work/grep_learn$ 

13. grep -l PATTERN… [FILE…]

不打印匹配的内容，而是打印FILE中匹配上的文件的名称

xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_*.c grep_file.c:test grep_test_2.c:test_2 grep_test_3.c:xxtest grep_test_3.c:testxx grep_test_3.c:_test grep_test_3.c:-test grep_test_3.c:test_3 grep_test_3.c:test test test grep_test_3.c:test_ grep_test_3.c:xxx xxx test- grep_test_3.c:This is a test file. grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_*.c -l grep_file.c grep_test_2.c grep_test_3.c grep_test.c xiaohui@ubuntu:~/work/grep_learn$ 

14. grep -m NUM PATTERN… [FILE…]

每个文件最多匹配出NUM行，

xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test_3.c -m 5 xxtest testxx _test -test test_3 xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test_3.c xxtest testxx _test -test test_3 test test test test_ xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_*.c -m 3 grep_file.c:test grep_test_2.c:test_2 grep_test_3.c:xxtest grep_test_3.c:testxx grep_test_3.c:_test grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ 

15. grep -o PATTERN… [FILE…]

仅打印匹配的内容，而不是匹配的一整行

xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test_3.c xxtest testxx _test -test test_3 test test test test_ xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test_3.c -o test test test test test test test test test test test xiaohui@ubuntu:~/work/grep_learn$ 

16. grep -q PATTERN… [FILE…]

不显示匹配结果，匹配结束立刻退出

xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test_3.c xxtest testxx _test -test test_3 test test test test_ xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test_3.c -q xiaohui@ubuntu:~/work/grep_learn$ 

17. grep -s PATTERN… [FILE…]

不显示文件不存在和读取失败的错误信息

xiaohui@ubuntu:~/work/grep_learn$ grep test file.c grep: file.c: No such file or directory xiaohui@ubuntu:~/work/grep_learn$ grep test file.c -s xiaohui@ubuntu:~/work/grep_learn$ xiaohui@ubuntu:~/work/grep_learn$ grep test /root/* grep: /root/*: Permission denied xiaohui@ubuntu:~/work/grep_learn$ grep test /root/* -s xiaohui@ubuntu:~/work/grep_learn$ 

18. grep -b PATTERN… [FILE…]

19. grep -H PATTERN… [FILE…]

20. grep -h PATTERN… [FILE…]

不显示文件名，单个文件匹配时，默认不显示文件名

xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test_3.c xxtest testxx _test -test test_3 test test test test_ xxx xxx test- This is a test file. xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test*.c grep_test_2.c:test_2 grep_test_3.c:xxtest grep_test_3.c:testxx grep_test_3.c:_test grep_test_3.c:-test grep_test_3.c:test_3 grep_test_3.c:test test test grep_test_3.c:test_ grep_test_3.c:xxx xxx test- grep_test_3.c:This is a test file. grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test*.c -h test_2 xxtest testxx _test -test test_3 test test test test_ xxx xxx test- This is a test file. -test test xiaohui@ubuntu:~/work/grep_learn$ 

21. grep -n PATTERN… [FILE…]

22. grep -T PATTERN… [FILE…]

显示时使用制表符

xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test*.c -n -H -b grep_test_2.c:14:57:test_2 grep_test_3.c:1:0:xxtest grep_test_3.c:2:7:testxx grep_test_3.c:3:14:_test grep_test_3.c:4:20:-test grep_test_3.c:5:26:test_3 grep_test_3.c:6:33:test test test grep_test_3.c:7:48:test_ grep_test_3.c:8:54:xxx xxx test- grep_test_3.c:9:69:This is a test file. grep_test.c:9:41:-test grep_test.c:10:47:test xiaohui@ubuntu:~/work/grep_learn$ grep "test" grep_test*.c -n -H -b -T grep_test_2.c: 14: 57 :test_2 grep_test_3.c: 1: 0 :xxtest grep_test_3.c: 2: 7 :testxx grep_test_3.c: 3: 14 :_test grep_test_3.c: 4: 20 :-test grep_test_3.c: 5: 26 :test_3 grep_test_3.c: 6: 33 :test test test grep_test_3.c: 7: 48 :test_ grep_test_3.c: 8: 54 :xxx xxx test- grep_test_3.c: 9: 69 :This is a test file. grep_test.c: 9: 41:-test grep_test.c: 10: 47:test xiaohui@ubuntu:~/work/grep_learn$ 

23. grep -Z PATTERN… [FILE…]

文件名后面的符号改为零字节（ASCII NUL字符）

xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test.c -H grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test.c -H -Z grep_test.c-test grep_test.ctest xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test* -Z -H -l grep_test_2.cgrep_test_3.cgrep_test.cxiaohui@ubuntu:~/work/grep_learn$ 

24. grep -A NUM PATTERN… [FILE…]

将匹配行后面的NUM行也打印出来

xiaohui@ubuntu:~/work/grep_learn$ grep TEST -A 0 grep_test.c TEST xiaohui@ubuntu:~/work/grep_learn$ grep TEST -A 1 grep_test.c TEST -test xiaohui@ubuntu:~/work/grep_learn$ grep TEST -A 2 grep_test.c TEST -test test xiaohui@ubuntu:~/work/grep_learn$ grep TEST -A 3 grep_test.c TEST -test test xiaohui@ubuntu:~/work/grep_learn$ 

25. grep -B NUM PATTERN… [FILE…]

将匹配行前面的NUM行也打印出来

xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test_2.c -B 0 test_2 xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test_2.c -B 1 text_2 test_2 xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test_2.c -B 2 90 text_2 test_2 xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test_2.c -B -1 grep: -1: invalid context length argument xiaohui@ubuntu:~/work/grep_learn$ 

26. grep -C NUM PATTERN… [FILE…]

将匹配行前面和后面的NUM行也打印出来

xiaohui@ubuntu:~/work/grep_learn$ grep TEXT grep_test.c -C 0 TEXT xiaohui@ubuntu:~/work/grep_learn$ grep TEXT grep_test.c -C 1 textxx TEXT TEST xiaohui@ubuntu:~/work/grep_learn$ grep TEXT grep_test.c -C 2 text* textxx TEXT TEST -test xiaohui@ubuntu:~/work/grep_learn$ grep TEXT grep_test.c -C 3 efg text* textxx TEXT TEST -test test xiaohui@ubuntu:~/work/grep_learn$ 

27. grep -a PATTERN… [FILE…]

28. grep –binary-files=TYPE PATTERN… [FILE…]

TYPE的值可以为：binary（默认）、without-match、text，binary和without-match的区别是前者使用时会提示二进制文件无法匹配，后者不会提示，–binary-files=text相当于-a选项。

xiaohui@ubuntu:~/work/grep_learn$ grep hello hello_grep.out --binary-files=without-match xiaohui@ubuntu:~/work/grep_learn$ grep hello hello_grep.out --binary-files=binary Binary file hello_grep.out matches xiaohui@ubuntu:~/work/grep_learn$ grep hello hello_grep.out --binary-files=text h������%� f�1�I��^H��H���PTI���@H��P@H��&@������fD�?`UH-8`H��H��v�H��t]�8`��f�]�@f.��8`UH��8`H��H��H��H��?H�H��t�H��t ]�8`��]�fD�=Q uUH���n���]�> ��@� `H�?u���H��t�UH����]�z���UH����@��������@�������]ÐAWAVA��AUATL�% UH�- SI��I��L)�H�H���G���H��t 1��L��L��D��A��H��H9�u�H�[]A\A]A^A_Ðf.���H�H��hello grephello world;0���|D���L:����d�������� zRx �����*zRx �$����0FJ d �?;*3$"D����)A�C Dd����eB�B�E �B(�H0�H8�M@r8A0A(B BB�����@�@ �@``���o�@@�@ �@ �@ ... 

29. grep -D ACTION PATTERN… [FILE…]

当FILE为设备文件、FIFO或套接字时，使用ACTION去处理它，ACTION默认为read，也可以为skip，前者将该文件作为普通文件处理，后者则跳过读取该文件。

先用mkfifo创建一个fifo件，将test字符串在后台写入：

xiaohui@ubuntu:~/work/grep_learn$ echo test > my_fifo & [1] 11012 xiaohui@ubuntu:~/work/grep_learn$ grep test my_fifo -D read test [1]+ Done echo test > my_fifo xiaohui@ubuntu:~/work/grep_learn$ echo test > my_fifo & [1] 11015 xiaohui@ubuntu:~/work/grep_learn$ grep test my_fifo -D skip xiaohui@ubuntu:~/work/grep_learn$ jobs [1]+ Broken pipe echo test > my_fifo xiaohui@ubuntu:~/work/grep_learn$ 

30. grep -d ACTION PATTERN… [FILE…]

当FILE为目录时，使用ACTION去处理它，ACTION默认为read，也可以为skip或recurse，ACTION为read时，grep将该文件作为普通文件处理，为skip时跳过读取该文件，为recurse时，递归读取所有文件。

xiaohui@ubuntu:~/work/grep_learn$ grep text dir/ grep: dir/: Is a directory xiaohui@ubuntu:~/work/grep_learn$ grep text dir/ -d read grep: dir/: Is a directory xiaohui@ubuntu:~/work/grep_learn$ grep text dir/ -d skip xiaohui@ubuntu:~/work/grep_learn$ grep text dir/ -d recurse dir/grep_test.c:text_0 dir/dir1/grep_test.c:text_1 dir/dir2/grep_test.c:text_2 xiaohui@ubuntu:~/work/grep_learn$ 

31. grep –exclude=GLOB PATTERN… [FILE…]

跳过与GLOB匹配的文件，文件名可以使用通配符

xiaohui@ubuntu:~/work/grep_learn$ grep test --exclude=grep_test_3.c grep_test*.cgrep_test_2.c:test_2 grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test*.cgrep_test_2.c:test_2 grep_test_3.c:xxtest grep_test_3.c:testxx grep_test_3.c:_test grep_test_3.c:-test grep_test_3.c:test_3 grep_test_3.c:test test test grep_test_3.c:test_ grep_test_3.c:xxx xxx test- grep_test_3.c:This is a test file. grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ 

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32. grep –exclude-from=FILE PATTERN… [FILE…]

从FILE（要匹配的文件）中排除与FILE（–exclude-from=选项中的FILE）文件内容匹配的文件

grep_test_4.c中有grep_test_3*，所以匹配时排除文件名与grep_test_3*匹配的文件

xiaohui@ubuntu:~/work/grep_learn$ cat grep_test_4.c xxxx grep_test_3* xiaohui@ubuntu:~/work/grep_learn$ grep test --exclude-from=grep_test_4.c grep_test*.c grep_test_2.c:test_2 grep_test_4.c:grep_test_3* grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ grep test grep_test*.cgrep_test_2.c:test_2 grep_test_3.c:xxtest grep_test_3.c:testxx grep_test_3.c:_test grep_test_3.c:-test grep_test_3.c:test_3 grep_test_3.c:test test test grep_test_3.c:test_ grep_test_3.c:xxx xxx test- grep_test_3.c:This is a test file. grep_test_4.c:grep_test_3* grep_test.c:-test grep_test.c:test xiaohui@ubuntu:~/work/grep_learn$ 

33. grep –exclude-dir=DIR PATTERN… [FILE…]

从FILE（目录文件）中排除目录名/文件名与DIR匹配的文件

xiaohui@ubuntu:~/work/grep_learn$ grep text --exclude-dir=dir ./ -r ./grep_test.c:text* ./grep_test.c:textxx ./grep_file.c:text ./text_0/grep_test.c:text_0 ./text_1/grep_test.c:text_0 ./grep_test_2.c:text_2 Binary file ./hello_grep.out matches xiaohui@ubuntu:~/work/grep_learn$ grep text ./ -r ./grep_test.c:text* ./grep_test.c:textxx ./grep_file.c:text ./text_0/grep_test.c:text_0 ./text_1/grep_test.c:text_0 ./grep_test_2.c:text_2 Binary file ./hello_grep.out matches ./dir/grep_test.c:text_0 ./dir/dir1/grep_test.c:text_1 ./dir/dir2/grep_test.c:text_2 xiaohui@ubuntu:~/work/grep_learn$ 

34. grep -I PATTERN… [FILE…]

同–binary-files=without-match，见28.grep –binary-files。

35. grep –include=GLOB PATTERN… [FILE…]

搜索文件名与GLOB匹配的文件（使用通配符匹配）

xiaohui@ubuntu:~/work/grep_learn$ grep test --include=grep_test_2* grep_test_*.c grep_test_2.c:test_2 xiaohui@ubuntu:~/work/grep_learn$ grep test --include=grep_test_4* grep_test_*.c grep_test_4.c:grep_test_3* xiaohui@ubuntu:~/work/grep_learn$ 

36. grep -r PATTERN… [FILE…]

同-d recurse选项，默认所在当前工作目录，遵循命令行符号链接，见30.grep -d ACTION。

37. grep -R PATTERN… [FILE…]

和-r类似，但遵循所有的符号链接

. 

man手册

以下为 grep 命令手册原文：

GREP(1) General Commands Manual GREP(1) NAME grep, egrep, fgrep, rgrep - print lines matching a pattern SYNOPSIS grep [OPTIONS] PATTERN [FILE...] grep [OPTIONS] [-e PATTERN]... [-f FILE]... [FILE...] DESCRIPTION grep searches the named input FILEs for lines containing a match to the given PATTERN. If no files are specified, or if the file “-” is given, grep searches standard input. By default, grep prints the matching lines. In addition, the variant programs egrep, fgrep and rgrep are the same as grep -E, grep -F, and grep -r, respectively. These variants are deprecated, but are provided for backward compatibility. OPTIONS Generic Program Information --help Output a usage message and exit. -V, --version Output the version number of grep and exit. Matcher Selection -E, --extended-regexp Interpret PATTERN as an extended regular expression (ERE, see below). -F, --fixed-strings Interpret PATTERN as a list of fixed strings (instead of regular expressions), separated by newlines, any of which is to be matched. -G, --basic-regexp Interpret PATTERN as a basic regular expression (BRE, see below). This is the default. -P, --perl-regexp Interpret the pattern as a Perl-compatible regular expression (PCRE). This is highly experimental and grep -P may warn of unimplemented features. Matching Control -e PATTERN, --regexp=PATTERN Use PATTERN as the pattern. If this option is used multiple times or is combined with the -f (--file) option, search for all patterns given. This option can be used to protect a pattern beginning with “-”. -f FILE, --file=FILE Obtain patterns from FILE, one per line. If this option is used multiple times or is combined with the -e (--regexp) option, search for all patterns given. The empty file contains zero patterns, and therefore matches nothing. -i, --ignore-case Ignore case distinctions in both the PATTERN and the input files. -v, --invert-match Invert the sense of matching, to select non-matching lines. -w, --word-regexp Select only those lines containing matches that form whole words. The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent character. Similarly, it must be either at the end of the line or followed by a non-word constituent character. Word-constituent characters are letters, digits, and the underscore. -x, --line-regexp Select only those matches that exactly match the whole line. For a regular expression pattern, this is like parenthesizing the pattern and then surrounding it with ^ and $. -y Obsolete synonym for -i. General Output Control -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. --color[=WHEN], --colour[=WHEN] Surround the matched (non-empty) strings, matching lines, context lines, file names, line numbers, byte offsets, and separators (for fields and groups of context lines) with escape sequences to display them in color on the terminal. The colors are defined by the environment variable GREP_COLORS. The deprecated environment variable GREP_COLOR is still supported, but its setting does not have priority. WHEN is never, always, or auto. -L, --files-without-match Suppress normal output; instead print the name of each input file from which no output would normally have been printed. The scanning will stop on the first match. -l, --files-with-matches Suppress normal output; instead print the name of each input file from which output would normally have been printed. The scanning will stop on the first match. -m NUM, --max-count=NUM Stop reading a file after NUM matching lines. If the input is standard input from a regular file, and NUM matching lines are output, grep ensures that the standard input is positioned to just after the last matching line before exiting, regardless of the presence of trailing context lines. This enables a calling process to resume a search. When grep stops after NUM matching lines, it outputs any trailing context lines. When the -c or --count option is also used, grep does not output a count greater than NUM. When the -v or --invert-match option is also used, grep stops after outputting NUM non-matching lines. -o, --only-matching Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line. -q, --quiet, --silent Quiet; do not write anything to standard output. Exit immediately with zero status if any match is found, even if an error was detected. Also see the -s or --no-messages option. -s, --no-messages Suppress error messages about nonexistent or unreadable files. Output Line Prefix Control -b, --byte-offset Print the 0-based byte offset within the input file before each line of output. If -o (--only-matching) is specified, print the offset of the matching part itself. -H, --with-filename Print the file name for each match. This is the default when there is more than one file to search. -h, --no-filename Suppress the prefixing of file names on output. This is the default when there is only one file (or only standard input) to search. --label=LABEL Display input actually coming from standard input as input coming from file LABEL. This is especially useful when implementing tools like zgrep, e.g., gzip -cd foo.gz | grep --label=foo -H something. See also the -H option. -n, --line-number Prefix each line of output with the 1-based line number within its input file. -T, --initial-tab Make sure that the first character of actual line content lies on a tab stop, so that the alignment of tabs looks normal. This is useful with options that prefix their output to the actual content: -H,-n, and -b. In order to improve the probability that lines from a single file will all start at the same column, this also causes the line number and byte offset (if present) to be printed in a minimum size field width. -u, --unix-byte-offsets Report Unix-style byte offsets. This switch causes grep to report byte offsets as if the file were a Unix-style text file, i.e., with CR characters stripped off. This will produce results identical to running grep on a Unix machine. This option has no effect unless -b option is also used; it has no effect on platforms other than MS-DOS and MS-Windows. -Z, --null Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name. For example, grep -lZ outputs a zero byte after each file name instead of the usual newline. This option makes the output unambiguous, even in the presence of file names containing unusual characters like newlines. This option can be used with commands like find -print0, perl -0, sort -z, and xargs -0 to process arbitrary file names, even those that contain newline characters. Context Line Control -A NUM, --after-context=NUM Print NUM lines of trailing context after matching lines. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given. -B NUM, --before-context=NUM Print NUM lines of leading context before matching lines. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given. -C NUM, -NUM, --context=NUM Print NUM lines of output context. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given. File and Directory Selection -a, --text Process a binary file as if it were text; this is equivalent to the --binary-files=text option. --binary-files=TYPE If the first few bytes of a file indicate that the file contains binary data, assume that the file is of type TYPE. By default, TYPE is binary, and grep normally outputs either a one-line message saying that a binary file matches, or no message if there is no match. If TYPE is without-match, grep assumes that a binary file does not match; this is equivalent to the -I option. If TYPE is text, grep processes a binary file as if it were text; this is equivalent to the -a option. When processing binary data, grep may treat non-text bytes as line terminators; for example, the pattern '.' (period) might not match a null byte, as the null byte might be treated as a line terminator. Warning: grep --binary-files=text might output binary garbage, which can have nasty side effects if the output is a terminal and if the terminal driver interprets some of it as commands. -D ACTION, --devices=ACTION If an input file is a device, FIFO or socket, use ACTION to process it. By default, ACTION is read, which means that devices are read just as if they were ordinary files. If ACTION is skip, devices are silently skipped. -d ACTION, --directories=ACTION If an input file is a directory, use ACTION to process it. By default, ACTION is read, i.e., read directories just as if they were ordinary files. If ACTION is skip, silently skip directories. If ACTION is recurse, read all files under each directory, recursively, following symbolic links only if they are on the command line. This is equivalent to the -r option. --exclude=GLOB Skip files whose base name matches GLOB (using wildcard matching). A file-name glob can use *, ?, and [...] as wildcards, and \ to quote a wildcard or backslash character literally. --exclude-from=FILE Skip files whose base name matches any of the file-name globs read from FILE (using wildcard matching as described under --exclude). --exclude-dir=DIR Exclude directories matching the pattern DIR from recursive searches. -I Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option. --include=GLOB Search only files whose base name matches GLOB (using wildcard matching as described under --exclude). -r, --recursive Read all files under each directory, recursively, following symbolic links only if they are on the command line. Note that if no file operand is given, grep searches the working directory. This is equivalent to the -d recurse option. -R, --dereference-recursive Read all files under each directory, recursively. Follow all symbolic links, unlike -r. Other Options --line-buffered Use line buffering on output. This can cause a performance penalty. -U, --binary Treat the file(s) as binary. By default, under MS-DOS and MS- Windows, grep guesses the file type by looking at the contents of the first 32KB read from the file. If grep decides the file is a text file, it strips the CR characters from the original file contents (to make regular expressions with ^ and $ work correctly). Specifying -U overrules this guesswork, causing all files to be read and passed to the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the end of each line, this will cause some regular expressions to fail. This option has no effect on platforms other than MS-DOS and MS- Windows. -z, --null-data Treat the input as a set of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline. Like the -Z or --null option, this option can be used with commands like sort -z to process arbitrary file names. REGULAR EXPRESSIONS A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions. grep understands three different versions of regular expression syntax: “basic” (BRE), “extended” (ERE) and “perl” (PCRE). In GNU grep, there is no difference in available functionality between basic and extended syntaxes. In other implementations, basic regular expressions are less powerful. The following description applies to extended regular expressions; differences for basic regular expressions are summarized afterwards. Perl-compatible regular expressions give additional functionality, and are documented in pcresyntax(3) and pcrepattern(3), but work only if PCRE is available in the system. The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any meta-character with special meaning may be quoted by preceding it with a backslash. The period . matches any single character. Character Classes and Bracket Expressions A bracket expression is a list of characters enclosed by [ and ]. It matches any single character in that list; if the first character of the list is the caret ^ then it matches any character not in the list. For example, the regular expression [0] matches any single digit. Within a bracket expression, a range expression consists of two characters separated by a hyphen. It matches any single character that sorts between the two characters, inclusive, using the locale's collating sequence and character set. For example, in the default C locale, [a-d] is equivalent to [abcd]. Many locales sort characters in dictionary order, and in these locales [a-d] is typically not equivalent to [abcd]; it might be equivalent to [aBbCcDd], for example. To obtain the traditional interpretation of bracket expressions, you can use the C locale by setting the LC_ALL environment variable to the value C. Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means the character class of numbers and letters in the current locale. In the C locale and ASCII character set encoding, this is the same as [0-9A-Za-z]. (Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket expression.) Most meta-characters lose their special meaning inside bracket expressions. To include a literal ] place it first in the list. Similarly, to include a literal ^ place it anywhere but first. Finally, to include a literal - place it last. Anchoring The caret ^ and the dollar sign $ are meta-characters that respectively match the empty string at the beginning and end of a line. The Backslash Character and Special Expressions The symbols \< and \> respectively match the empty string at the beginning and end of a word. The symbol \b matches the empty string at the edge of a word, and \B matches the empty string provided it's not at the edge of a word. The symbol \w is a synonym for [_[:alnum:]] and \W is a synonym for [^_[:alnum:]]. Repetition A regular expression may be followed by one of several repetition operators: ? The preceding item is optional and matched at most once. * The preceding item will be matched zero or more times. + The preceding item will be matched one or more times. {n} The preceding item is matched exactly n times. {n,} The preceding item is matched n or more times. {,m} The preceding item is matched at most m times. This is a GNU extension. {n,m} The preceding item is matched at least n times, but not more than m times. Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated expressions. Alternation Two regular expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either alternate expression. Precedence Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole expression may be enclosed in parentheses to override these precedence rules and form a subexpression. Back References and Subexpressions The back-reference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular expression. Basic vs Extended Regular Expressions In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \). ENVIRONMENT VARIABLES The behavior of grep is affected by the following environment variables. The locale for category LC_foo is specified by examining the three environment variables LC_ALL, LC_foo, LANG, in that order. The first of these variables that is set specifies the locale. For example, if LC_ALL is not set, but LC_MESSAGES is set to pt_BR, then the Brazilian Portuguese locale is used for the LC_MESSAGES category. The C locale is used if none of these environment variables are set, if the locale catalog is not installed, or if grep was not compiled with national language support (NLS). GREP_OPTIONS This variable specifies default options to be placed in front of any explicit options. As this causes problems when writing portable scripts, this feature will be removed in a future Concatenation release of grep, and grep warns if it is used. Please use an alias or script instead. GREP_COLOR This variable specifies the color used to highlight matched (non-empty) text. It is deprecated in favor of GREP_COLORS, but still supported. The mt, ms, and mc capabilities of GREP_COLORS have priority over it. It can only specify the color used to highlight the matching non-empty text in any matching line (a selected line when the -v command-line option is omitted, or a context line when -v is specified). The default is 01;31, which means a bold red foreground text on the terminal's default background. GREP_COLORS Specifies the colors and other attributes used to highlight various parts of the output. Its value is a colon-separated list of capabilities that defaults to ms=01;31:mc=01;31:sl=:cx=:fn=35:ln=32:bn=32:se=36 with the rv and ne boolean capabilities omitted (i.e., false). Supported capabilities are as follows. sl= SGR substring for whole selected lines (i.e., matching lines when the -v command-line option is omitted, or non- matching lines when -v is specified). If however the boolean rv capability and the -v command-line option are both specified, it applies to context matching lines instead. The default is empty (i.e., the terminal's default color pair). cx= SGR substring for whole context lines (i.e., non-matching lines when the -v command-line option is omitted, or matching lines when -v is specified). If however the boolean rv capability and the -v command-line option are both specified, it applies to selected non-matching lines instead. The default is empty (i.e., the terminal's default color pair). rv Boolean value that reverses (swaps) the meanings of the sl= and cx= capabilities when the -v command-line option is specified. The default is false (i.e., the capability is omitted). mt=01;31 SGR substring for matching non-empty text in any matching line (i.e., a selected line when the -v command-line option is omitted, or a context line when -v is specified). Setting this is equivalent to setting both ms= and mc= at once to the same value. The default is a bold red text foreground over the current line background. ms=01;31 SGR substring for matching non-empty text in a selected line. (This is only used when the -v command-line option is omitted.) The effect of the sl= (or cx= if rv) capability remains active when this kicks in. The default is a bold red text foreground over the current line background. mc=01;31 SGR substring for matching non-empty text in a context line. (This is only used when the -v command-line option is specified.) The effect of the cx= (or sl= if rv) capability remains active when this kicks in. The default is a bold red text foreground over the current line background. fn=35 SGR substring for file names prefixing any content line. The default is a magenta text foreground over the terminal's default background. ln=32 SGR substring for line numbers prefixing any content line. The default is a green text foreground over the terminal's default background. bn=32 SGR substring for byte offsets prefixing any content line. The default is a green text foreground over the terminal's default background. se=36 SGR substring for separators that are inserted between selected line fields (:), between context line fields, (-), and between groups of adjacent lines when nonzero context is specified (--). The default is a cyan text foreground over the terminal's default background. ne Boolean value that prevents clearing to the end of line using Erase in Line (EL) to Right (\33[K) each time a colorized item ends. This is needed on terminals on which EL is not supported. It is otherwise useful on terminals for which the back_color_erase (bce) boolean terminfo capability does not apply, when the chosen highlight colors do not affect the background, or when EL is too slow or causes too much flicker. The default is false (i.e., the capability is omitted). Note that boolean capabilities have no =... part. They are omitted (i.e., false) by default and become true when specified. See the Select Graphic Rendition (SGR) section in the documentation of the text terminal that is used for permitted values and their meaning as character attributes. These substring values are integers in decimal representation and can be concatenated with semicolons. grep takes care of assembling the result into a complete SGR sequence (\33[...m). Common values to concatenate include 1 for bold, 4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color modes foreground colors, 49 for default background color, 40 to 47 for background colors, 100 to 107 for 16-color mode background colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes background colors. LC_ALL, LC_COLLATE, LANG These variables specify the locale for the LC_COLLATE category, which determines the collating sequence used to interpret range expressions like [a-z]. LC_ALL, LC_CTYPE, LANG These variables specify the locale for the LC_CTYPE category, which determines the type of characters, e.g., which characters are whitespace. LC_ALL, LC_MESSAGES, LANG These variables specify the locale for the LC_MESSAGES category, which determines the language that grep uses for messages. The default C locale uses American English messages. POSIXLY_CORRECT These variables specify the locale for the LC_MESSAGES category, which determines the language that grep uses for messages. The default C locale uses American English messages. POSIXLY_CORRECT If set, grep behaves as POSIX requires; otherwise, grep behaves more like other GNU programs. POSIX requires that options that follow file names must be treated as file names; by default, such options are permuted to the front of the operand list and are treated as options. Also, POSIX requires that unrecognized options be diagnosed as “illegal”, but since they are not really against the law the default is to diagnose them as “invalid”. POSIXLY_CORRECT also disables _N_GNU_nonoption_argv_flags_, described below. _N_GNU_nonoption_argv_flags_ (Here N is grep's numeric process ID.) If the ith character of this environment variable's value is 1, do not consider the ith operand of grep to be an option, even if it appears to be one. A shell can put this variable in the environment for each command it runs, specifying which operands are the results of file name wildcard expansion and therefore should not be treated as options. This behavior is available only with the GNU C library, and only when POSIXLY_CORRECT is not set. EXIT STATUS Normally the exit status is 0 if a line is selected, 1 if no lines were selected, and 2 if an error occurred. However, if the -q or --quiet or --silent is used and a line is selected, the exit status is 0 even if an error occurred. COPYRIGHT Copyright 1998-2000, 2002, 2005-2016 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. BUGS Reporting Bugs Email bug reports to the bug-reporting address ⟨⟩. An email archive ⟨http://lists.gnu.org/mailman/listinfo/bug-grep⟩ and a bug tracker ⟨http://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep⟩ are available. Known Bugs Large repetition counts in the {n,m} construct may cause grep to use lots of memory. In addition, certain other obscure regular expressions require exponential time and space, and may cause grep to run out of memory. Back-references are very slow, and may require exponential time. SEE ALSO Regular Manual Pages awk(1), cmp(1), diff(1), find(1), gzip(1), perl(1), sed(1), sort(1), xargs(1), zgrep(1), read(2), pcre(3), pcresyntax(3), pcrepattern(3), terminfo(5), glob(7), regex(7). POSIX Programmer's Manual Page grep(1p). Full Documentation A complete manual ⟨http://www.gnu.org/software/grep/manual/⟩ is available. If the info and grep programs are properly installed at your site, the command info grep should give you access to the complete manual. NOTES This man page is maintained only fitfully; the full documentation is often more up-to-date. User Commands GNU grep 2.25 GREP(1)