Linux下文本搜索工具grep命令使用入门

grep命令入门

如果想通过使用grep命令来实现理想化的文本搜索，对正则表达式的了解是比不可少的。文献1对正则表达式语法做了一个简单的介绍，文献2提供了一个简单的入门。码农也可以自己google一下其他的参考资料。下面就grep命令的使用做个入门级的介绍。

1.1 grep命令的变种

linux下除了grep命令可以完成文本搜索外，还存在egrep，fgrep，rgrep三个命令。这三个命令都是由grep加上一些控制参数演变而来，如egrep=grep -E, fgrep=grep -F, rgrep=grep -r(后面会介绍这些参数)，所以以码农只需关注于grep命令即可。

1.2 grep命令的使用格式

（1）grep [OPTIONS] PATTERN [FILE...]

（2）grep [OPTIONS] [-e PATTERN | -f PATTERN] [FILE...]

示例：

grep hello hello.c //查找hello.c文件中含有hello的代码行grep -e hello -e world hello.c //查找文件中含有hello或world的代码行grep -f hello hello.c //从文件hello中读取搜索关键词，然后在文件hello.c中查找此关键词

1.3 grep命令的参数选择

匹配选择：

-E, --extended-regexp 将PATTERN作为扩展的正则表达式解释，如grep -E '^\s' hello.c // 搜索hello.c文件中以空白字符开始的行，相当于egrep '^\s' hello.c

-F, --fixed-strings 将PATTERN解释为固定的字符串，不作正则表达式分析。grep -F 'main()' hello.c // 等同于fgrep 'main()' hello.c

匹配控制：

-e PATTERN, --regexp=PATTERN 指定pattern为搜索正则表达式，可以通过使用这个选项来指定多个搜索模式，或者用来制定以横线-开始的搜索模式，如grep -e hello -e world hello.c //搜索含有hello或者world的代码行

-f file, --file=FILE 指定从文件FILE中读取搜索模式，一行一个搜索模式

-i, --ignore-case模式匹配时忽略大小写

-v, --invert-math 反向匹配，选择那些不含有匹配模式的行，如grep -e -v hello hello.c //输出那些不含有hello的代码行

-x, --line-regexp 将一整行文本与搜索模式PATTERN进行匹配，输出匹配行，如grep -E '^\s*$' -x hello.c //查找空白行

输出控制：

-c, --count代替输出匹配的文本行，还是输出匹配的次数

-m NUM, --max-count=NUM 在一个文件中匹配次数超过NUM后，就停止搜索匹配

-o, --only-matching 代替输出匹配的文本行，而是仅仅输出匹配的部分文本

-n, --line-number 在输出的匹配文本行前面添加行号，这个行号指的原文件中的文本所在行号

其它：

-R, -r, --recursive 递归地从目录下的每个文件搜索匹配PATTERN，如grep -r hello . -n 10 //在当前目录下的每个文件（包括子目录中的文件）搜索单词hello，当在一个文件中匹配次数超过10次时，立即退出当前文件，对下一个文件进行搜索匹配

-d ACTION, --devices=ACTION 如果搜索文件是一个目录，使用ACTION来处理它。ACTION是read时，将目录文件当作普通文件；是skip时，将目录文件跳过；是recurse时，则递归地读取目录下的所有文件；grep hello -d recurse . //相当于grep hello -r .

注：rgrep hello . = grep hello -r . = grep hello -d recurse .

参考文献：

文献1：http://msdn.microsoft.com/zh-cn/library/ae5bf541(v=vs.90).aspx

文献2：http://regex.bastardsbook.com/

文献3：http://my.oschina.net/wenhaowu/blog/219956

附上手册：

GREP(1)                                                                GREP(1)NAME       grep, egrep, fgrep, rgrep - print lines matching a patternSYNOPSIS       grep [OPTIONS] PATTERN [FILE...]       grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]DESCRIPTION       grep  searches the named input FILEs (or standard input if no files are       named, or if a single hyphen-minus (-) is given as file name) for lines       containing  a  match to the given PATTERN.  By default, grep prints the       matching lines.       In  addition,  three  variant  programs  egrep,  fgrep  and  rgrep  are       available.   egrep  is  the  same  as  grep -E.   fgrep  is the same as       grep -F.  rgrep is the same as grep -r.  Direct  invocation  as  either       egrep  or  fgrep  is  deprecated,  but  is provided to allow historical       applications that rely on them to run unmodified.OPTIONS   Generic Program Information       --help Print a usage message  briefly  summarizing  these  command-line              options and the bug-reporting address, then exit.       -V, --version              Print  the version number of grep to the standard output stream.              This version number should be included in all bug  reports  (see              below).   Matcher Selection       -E, --extended-regexp              Interpret  PATTERN  as  an extended regular expression (ERE, see              below).  (-E is specified by POSIX.)       -F, --fixed-strings              Interpret PATTERN as a  list  of  fixed  strings,  separated  by              newlines,  any  of  which is to be matched.  (-F is specified by              POSIX.)       -G, --basic-regexp              Interpret PATTERN  as  a  basic  regular  expression  (BRE,  see              below).  This is the default.       -P, --perl-regexp              Interpret  PATTERN  as  a  Perl  regular  expression  (PCRE, see              below).  This is highly experimental and grep  -P  may  warn  of              unimplemented features.   Matching Control       -e PATTERN, --regexp=PATTERN              Use  PATTERN  as  the  pattern.   This  can  be  used to specify              multiple search patterns, or to protect a pattern beginning with              a hyphen (-).  (-e is specified by POSIX.)       -f FILE, --file=FILE              Obtain  patterns  from  FILE,  one  per  line.   The  empty file              contains zero patterns, and therefore matches nothing.   (-f  is              specified by POSIX.)       -i, --ignore-case              Ignore  case  distinctions  in  both  the  PATTERN and the input              files.  (-i is specified by POSIX.)       -v, --invert-match              Invert the sense of matching, to select non-matching lines.  (-v              is specified by POSIX.)       -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.              (-x is specified by POSIX.)       -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.  (-c is specified by POSIX.)       --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.  (-l is specified by              POSIX.)       -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.              (-q is specified by POSIX.)       -s, --no-messages              Suppress  error  messages about nonexistent or unreadable files.              Portability note: unlike GNU grep, 7th Edition Unix grep did not              conform to POSIX, because it lacked -q and its -s option behaved              like GNU grep's -q option.  USG-style grep also  lacked  -q  but              its  -s  option  behaved  like GNU grep.  Portable shell scripts              should avoid both -q and -s and  should  redirect  standard  and              error output to /dev/null instead.  (-s is specified by POSIX.)   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.  (-n is specified by POSIX.)       -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.  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, which means that directories  are  read              just  as  if  they  were  ordinary  files.   If  ACTION is skip,              directories are silently skipped.  If ACTION  is  recurse,  grep              reads  all  files  under  each  directory,  recursively; 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, -r, --recursive              Read all  files  under  each  directory,  recursively;  this  is              equivalent to the -d recurse option.   Other Options       --line-buffered              Use  line  buffering  on  output.   This can cause a performance              penalty.       --mmap If possible, use the mmap(2) system call to read input,  instead              of  the default read(2) system call.  In some situations, --mmap              yields better performance.  However, --mmap can cause  undefined              behavior  (including  core dumps) if an input file shrinks while              grep is operating, or if an I/O error occurs.       -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” (PRCE). 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  regular  expressions give additional functionality,       and are documented in pcresyntax(3) and pcrepattern(3), but may not  be       available on every 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 [0123456789] 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.       {n,m}  The  preceding  item  is  matched at least n times, but not more              than m times.   Concatenation       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  \?,       \+, \{, \|, \(, and \).       Traditional  egrep did not support the { meta-character, and some egrep       implementations support \{ instead, so portable scripts should avoid  {       in grep -E patterns and should use [{] to match a literal {.       GNU grep -E attempts to support traditional usage by assuming that { is       not  special  if  it  would  be  the  start  of  an  invalid   interval       specification.   For example, the command grep -E '{1' searches for the       two-character string {1 instead of reporting  a  syntax  error  in  the       regular  expression.  POSIX.2 allows this behavior as an extension, but       portable scripts should avoid it.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.    For  example,  if  GREP_OPTIONS  is              '--binary-files=without-match --directories=skip', grep  behaves              as   if   the   two   options  --binary-files=without-match  and              --directories=skip  had  been  specified  before  any   explicit              options.   Option specifications are separated by whitespace.  A              backslash escapes the next character,  so  it  can  be  used  to              specify an option containing whitespace or a backslash.       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              If  set,  grep  behaves  as  POSIX.2  requires;  otherwise, grep              behaves more like other GNU  programs.   POSIX.2  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.2 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       The exit status is 0 if selected lines are found, and 1 if  not  found.       If an error occurred the exit status is 2.  (Note: POSIX error handling       code should check for '2' or greater.)COPYRIGHT       Copyright 1998-2000, 2002, 2005-2011 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 <[e-mail]>, a mailing list whose web  page       is  <http://lists.gnu.org/mailman/listinfo/bug-grep>.   grep's Savannah       bug tracker is located at <http://savannah.gnu.org/bugs/?group=grep>.   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),   mmap(2),   read(2),   pcre(3),   pcresyntax(3),       pcrepattern(3), terminfo(5), glob(7), regex(7).   POSIX Programmer's Manual Page       grep(1p).   TeXinfo Documentation       The  full documentation for grep is maintained as a TeXinfo manual.  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       GNU's not Unix, but Unix is a beast; its plural form is Unixen.User Commands                    GNU grep 2.10                         GREP(1)