GREP(1)                                                                GREP(1)

NAME
       grep, egrep, fgrep - print lines matching a pattern

SYNOPSIS
       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 the file name - is given) for lines containing a match to the
       given PATTERN.  By default, grep prints the matching lines.

       In addition, two variant programs egrep and fgrep are available.  Egrep is the same as grep -E.  Fgrep is the same as grep -F.

OPTIONS
       -A NUM, --after-context=NUM
              Print NUM lines of trailing context after matching lines.  Places a line containing -- between contiguous groups of matches.

itnihao注释===================================================

-A 行数  匹配字符串 文件

举例:grep -A 2 mark example   意思是从匹配文件example中mark的行往后数两行的所有行=========================================================

       -a, --text
              Process a binary file as if it were text; this is equivalent to the --binary-files=text option.

=============================================================

          grep原本是搜寻文字档,若拿二进位的档案作为搜寻的目标,
               则会显示如下的讯息: Binary file 二进位档名 matches 然後结束。
                  
               若加上-a参数则可将二进位档案视为文字档案搜寻,
               相当於--binary-files=text这个参数。

grep -a 匹配字符串 二进制文件;如果没有-a,则无法搜索

举例

[root@localhost bin]# grep echo /bin/echo
Binary file /bin/echo matches
[root@localhost bin]# grep -a echo /bin/echo
echo
@     

 =============================================================

       -B NUM, --before-context=NUM
              Print NUM lines of leading context before matching lines.  Places a line containing -- between contiguous groups of matches.

======================================

-B NUM,--before-context=NUM
               与 -A NUM 相对,但这此参数是显示除符合行之外
               并显示在它之前的NUM行。

[root@localhost ~]# grep -B 1 1234 test
123
1234
--
5555
123456
[root@localhost ~]# cat test
1
2
3
4
12
123
1234
1235
5555
123456
22222
666

=====================================================

       -C NUM, --context=NUM
              Print NUM lines of output context.  Places a line containing -- between contiguous groups of matches.

       -b, --byte-offset
              Print the byte offset within the input file before each line of output.

       --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  pro-
              cesses  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.

       --colour[=WHEN], --color[=WHEN]
              Surround the matching string with the marker find in GREP_COLOR environment variable. WHEN may be ‘never’, ‘always’, or ‘auto’

       -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.

       -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.

       -E, --extended-regexp
              Interpret PATTERN as an extended regular expression (see below).

       -e PATTERN, --regexp=PATTERN
              Use PATTERN as the pattern; useful to protect patterns beginning with -.

       -F, --fixed-strings
              Interpret PATTERN as a list of fixed strings, separated by newlines, any of which is to be matched.

       -P, --perl-regexp
              Interpret PATTERN as a Perl regular expression.

       -f FILE, --file=FILE
              Obtain patterns from FILE, one per line.  The empty file contains zero patterns, and therefore matches nothing.

       -G, --basic-regexp
              Interpret PATTERN as a basic regular expression (see below).  This is the default.

       -H, --with-filename
              Print the filename for each match.

       -h, --no-filename
              Suppress the prefixing of filenames on output when multiple files are searched.

       --help Output a brief help message.

       -I     Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option.

       -i, --ignore-case
              Ignore case distinctions in both the PATTERN and the input files.

       -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.

       --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 operat-
              ing, or if an I/O error occurs.

       -n, --line-number
              Prefix each line of output with the line number within its input file.

       -o, --only-matching
              Show only the part of a matching line that matches PATTERN.

       --label=LABEL
              Displays input actually coming from standard input as input coming from file LABEL.  This is especially useful  for  tools  like  zgrep,
              e.g.  gzip -cd foo.gz |grep -H --label=foo something

       --line-buffered
              Use line buffering, it can be a performance penality.

       -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.

       -R, -r, --recursive
              Read all files under each directory, recursively; this is equivalent to the -d recurse option.

         --include=PATTERN
              Recurse in directories only searching file matching PATTERN.

         --exclude=PATTERN
              Recurse in directories skip file matching PATTERN.

       -s, --no-messages
              Suppress error messages about nonexistent or unreadable files.  Portability note: unlike GNU grep, traditional grep did not  conform  to
              POSIX.2,  because traditional grep lacked a -q option and its -s option behaved like GNU grep’s -q option.  Shell scripts intended to be
              portable to traditional grep should avoid both -q and -s and should redirect output to /dev/null instead.

       -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.

       -u, --unix-byte-offsets
              Report Unix-style byte offsets.  This switch causes grep to report byte offsets as if the file were 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.

       -V, --version
              Print the version number of grep to standard error.  This version number should be included in all bug reports (see below).

       -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  begin-
              ning 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.

       -y     Obsolete synonym for -i.

       -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.

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 two different versions of regular expression syntax: “basic” and “extended.”  In GNU grep, there is no difference in available
       functionality  using  either syntax.  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.

       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 metacharacter with special meaning may be quoted by preceding it with a backslash.

       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  [0-9A-Za-z], except the latter form depends upon the C locale and the ASCII character encoding, whereas the former is inde-
       pendent of locale and character set.  (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 list.)  Most metacharacters lose their special meaning inside lists.  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.

       The period .  matches any single character.  The symbol \w is a synonym for [[:alnum:]] and \W is a synonym for [^[:alnum]].

       The caret ^ and the dollar sign $ are metacharacters that respectively match the empty string at the beginning and end of a line.  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.

       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.

       Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating  two  substrings  that
       respectively match the concatenated subexpressions.

       Two  regular  expressions may be joined by the infix operator |; the resulting regular expression matches any string matching either subexpres-
       sion.

       Repetition takes precedence over concatenation, which in turn takes precedence over alternation.  A whole  subexpression  may  be  enclosed  in
       parentheses to override these precedence rules.

       The backreference \n, where n is a single digit, matches the substring previously matched by the nth parenthesized subexpression of the regular
       expression.

       In basic regular expressions the metacharacters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions  \?,  \+,
       \{, \|, \(, and \).

       Traditional egrep did not support the { metacharacter, and some egrep implementations support \{ instead, so portable scripts should avoid { in
       egrep patterns and should use [{] to match a literal {.

       GNU egrep attempts to support traditional usage by assuming that { is not special if it would be the start of an  invalid  interval  specifica-
       tion.   For  example,  the shell command egrep ’{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
       Grep’s behavior is affected by the following environment variables.

       A locale 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 Brazilian Portuguese is used for
       the LC_MESSAGES locale.  The C locale is used if none of these environment variables are set, or 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
              Specifies the marker for highlighting.

       LC_ALL, LC_COLLATE, LANG
              These variables specify the LC_COLLATE locale, which determines the collating sequence used to interpret range expressions like [a-z].

       LC_ALL, LC_CTYPE, LANG
              These variables specify the LC_CTYPE locale, which determines the type of characters, e.g., which characters are whitespace.

       LC_ALL, LC_MESSAGES, LANG
              These variables specify the LC_MESSAGES locale, 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 fol-
              low 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, spec-
              ifying 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.

DIAGNOSTICS
       Normally,  exit  status  is  0  if  selected  lines are found and 1 otherwise.  But the exit status is 2 if an error occurred, unless the -q or
       --quiet or --silent option is used and a selected line is found.

BUGS
       Email bug reports to bug-grep@gnu.org.

       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.

       Backreferences are very slow, and may require exponential time.

GNU Project                       2002/01/22                           GREP(1)

 

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