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  • [리눅스/Linux] 명령어 - grep
    IT/리눅스 (Linux) 2023. 5. 15. 19:43
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    [grep]

    - 특정 문자열이 있는 라인 추출 또는 파일들에서 특정 문자열 검색

    - 사용법1) (명령어) | grep (단어)

    - 사용법2) grep [옵션] (검색 패턴) [파일1 파일2 ...]

     

    -r, --recursive 하위 디렉토리 검색
    -n, --line-number 포함된 단어가 있는 라인번호 출력
    -i, --ignore-case 대소문자 무시
    -v, --invert-match 일치하지 않는 라인 표시 (NOT)
    -c, --count 검색 단어와 일치하는 라인 개수를 표시
    -m NUM, --max-count=NUM 검색 개수 제한
    -o, --only-matching 검색결과를 라인 대신 검색 단어로만 출력
    -h, --no-filename
    -H, --with-filename
    검색시 파일명 미표시 (-h, 검색 결과 내용만 보여줌)
    검색시 파일명 표시 (-H, grep 실행시 기본옵션)
    -A NUM, --after-context=NUM
    -B NUM, --before-context=NUM
    검색된 단어 이후/이전의 라인을 표시
    -E, --extended-regexp
    -P, --perl-regexp
    AND/OR, 특수 패턴 등을 검색시 사용

    (AND) .* (OR) |
    -l, --files-with-matches
    -L, --files-without-match
    검색 단어가 포함된 파일리스트를 보여주기 (-l)
    검색 단어가 포함되지 않은 파일리스트를 보여주기 (-L)

     

    [root@linux ~]# cat /etc/hosts
    127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
    ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
    [root@linux ~]# cat /etc/hosts | grep 127
    127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4

     

    - 특정 문자열이 있는 파일 검색 [grep -rn (검색할 단어) (경로)]

    ▷ n 옵션은 파일내 몇번째 라인에 있는지 표시

    ▷ r 옵션은 경로내 하위 디렉토리를 포함하여 파일들을 검색

    [root@linux ~]# grep -rn limits /etc
    ...(생략)...
    /etc/pam.d/fingerprint-auth-ac:16:session     required      pam_limits.so
    /etc/pam.d/runuser:4:session            required        pam_limits.so
    /etc/pam.d/smartcard-auth-ac:16:session     required      pam_limits.so
    /etc/pam.d/password-auth-ac:22:session     required      pam_limits.so
    /etc/pam.d/system-auth-ac:20:session     required      pam_limits.so
    /etc/postfix/main.cf:343:# limit, this limits the mail inflow to 100 messages a second more
    /etc/security/pwquality.conf:1:# Configuration for systemwide password quality limits
    /etc/security/limits.conf:1:# /etc/security/limits.conf
    ...(생략)...

     

    - 검색 단어와 일치하는 라인수를 표시 (-c)

    [root@linux ~]# grep limits /etc/pam.d/* -c
    /etc/pam.d/chfn:0
    /etc/pam.d/chsh:0
    /etc/pam.d/config-util:0
    /etc/pam.d/crond:0
    /etc/pam.d/fingerprint-auth:1
    /etc/pam.d/fingerprint-auth-ac:1
    /etc/pam.d/login:0
    /etc/pam.d/newrole:0
    /etc/pam.d/other:0
    /etc/pam.d/passwd:0
    /etc/pam.d/password-auth:1
    /etc/pam.d/password-auth-ac:1
    /etc/pam.d/remote:0
    /etc/pam.d/run_init:0
    /etc/pam.d/runuser:1
    /etc/pam.d/runuser-l:0
    /etc/pam.d/smartcard-auth:1
    /etc/pam.d/smartcard-auth-ac:1
    /etc/pam.d/smtp:0
    /etc/pam.d/smtp.postfix:0
    /etc/pam.d/sshd:0
    /etc/pam.d/ssh-keycat:0
    /etc/pam.d/su:0
    /etc/pam.d/sudo:1
    /etc/pam.d/sudo-i:1
    /etc/pam.d/su-l:0
    /etc/pam.d/system-auth:1
    /etc/pam.d/system-auth-ac:1
    /etc/pam.d/vmtoolsd:0

     

    - 검색 단어 포함여부에 따른 파일리스트 보기 (-l, -L)

    ▷ -l : 검색단어 포함 / -L : 검색단어가 포함되지 않음

    [root@linux ~]# grep -L -r "limits the core" /etc/security/*
    /etc/security/access.conf
    /etc/security/chroot.conf
    /etc/security/console.handlers
    /etc/security/console.perms
    /etc/security/group.conf
    /etc/security/limits.d/90-nproc.conf
    /etc/security/namespace.conf
    /etc/security/namespace.init
    /etc/security/opasswd
    /etc/security/pam_env.conf
    /etc/security/sepermit.conf
    /etc/security/time.conf
    [root@linux ~]# grep -l -r "limits the core" /etc/security/*
    /etc/security/limits.conf

     

    - 검색 단어 개수를 제한 (-m (숫자))

    ▷ 제한 갯수만큼 출력 후 검색 중단

    [root@linux ~]# grep -r 'limits' /etc/security/*
    /etc/security/limits.conf:# /etc/security/limits.conf
    /etc/security/limits.conf:#        - "soft" for enforcing the soft limits
    /etc/security/limits.conf:#        - "hard" for enforcing hard limits
    /etc/security/limits.conf:#        - core - limits the core file size (KB)
    [root@linux ~]# grep -r -m 2 'limits' /etc/security/*
    /etc/security/limits.conf:# /etc/security/limits.conf
    /etc/security/limits.conf:#        - "soft" for enforcing the soft limits

     

    - 검색결과를 라인 대신 검색 단어로만 출력 (-o)

    [root@linux ~]# cat /etc/hosts.allow | grep -P 'access|rules'
    # hosts.allow   This file contains access rules which are used to
    #               See 'man 5 hosts_options' and 'man 5 hosts_access'
    [root@linux ~]# cat /etc/hosts.allow | grep -o -P 'access|rules'
    access
    rules
    access

     

    - 검색시 파일명 표시여부 (-h, -H)

    -H : 표시 (grep 명령 실행시 기본값)

    -h : 파일 미표시 (라인 내용만 보여주기)

    [root@linux ~]# grep -r -h 'limits' /etc/security/*
    # /etc/security/limits.conf
    #        - "soft" for enforcing the soft limits
    #        - "hard" for enforcing hard limits
    #        - core - limits the core file size (KB)
    [root@linux ~]# grep -r -H 'limits' /etc/security/*
    /etc/security/limits.conf:# /etc/security/limits.conf
    /etc/security/limits.conf:#        - "soft" for enforcing the soft limits
    /etc/security/limits.conf:#        - "hard" for enforcing hard limits
    /etc/security/limits.conf:#        - core - limits the core file size (KB)

     

    - 여러 단어가 모두 포함된 라인을 검색 (-P, AND 조건)

    ▷ grep -P '(단어1).*(단어2)....'

    ▷ 아래 예제는 줄 단위 검색시 'access', 'rules' 라는 두 단어가 반드시 포함된 경우에 출력

    3개 이상의 조건은 사용불가. 편법으로 grep 을 연속으로 사용

    [root@linux ~]# cat /etc/hosts.allow | grep -P 'access.*rules'
    # hosts.allow   This file contains access rules which are used to

     

    - 여러 단어를 한번에 검색 (-P, OR 조건) 

    ▷ grep -P '(단어1)|(단어2)....'

    ▷ 아래 예제는 줄 단위 검색시 'access' 및 'connections' 라는 두 단어중 하나만 검출되도 결과 출력

    3개 이상의 조건은 사용불가

    [root@linux ~]# cat /etc/hosts.allow | grep access
    # hosts.allow   This file contains access rules which are used to
    #               See 'man 5 hosts_options' and 'man 5 hosts_access'
    [root@linux ~]# cat /etc/hosts.allow | grep -P 'access|connections'
    # hosts.allow   This file contains access rules which are used to
    #               allow or deny connections to network services that
    #               See 'man 5 hosts_options' and 'man 5 hosts_access

     

    - 검색된 라인 전/후의 내용을 출력 (-A, -B)

    ▷ -A {라인수} : 검색된 라인 이후에 기입된 라인 수만큼 출력

    ▷ -B {라인수} : 검색된 라인 이전의 기입된 라인 수만큼 출력

    root@linux etc]# cat rsyncd.conf
    # /etc/rsyncd: configuration file for rsync daemon mode
    
    # See rsyncd.conf man page for more options.
    
    # configuration example:
    
    # uid = nobody
    # gid = nobody
    # use chroot = yes
    # max connections = 4
    # pid file = /var/run/rsyncd.pid
    # exclude = lost+found/
    # transfer logging = yes
    # timeout = 900
    # ignore nonreadable = yes
    # dont compress   = *.gz *.tgz *.zip *.z *.Z *.rpm *.deb *.bz2
    
    # [ftp]
    #        path = /home/ftp
    #        comment = ftp export area
    [root@linux etc]# grep -A 3 chroot rsyncd.conf
    # use chroot = yes
    # max connections = 4
    # pid file = /var/run/rsyncd.pid
    # exclude = lost+found/
    [root@linux etc]# grep -B 2 chroot rsyncd.conf
    # uid = nobody
    # gid = nobody
    # use chroot = yes

     

     

     

    - 띄어쓰기 단어를 하나로 묶으려면 묶음 처리 (')(")

    - 쉘스크립트 작성시 주의할 것

    ▷ ' 싱글 쿼터는 변수를 인식못함

    ▷ " 더블 쿼터는 변수 인식가능 

    [root@linux ~]# grep -r 'limits the core' /etc/security/*
    /etc/security/limits.conf:#        - core - limits the core file size (KB)
    
    [root@linux ~]# A=core
    [root@linux ~]# grep -r 'limits the $A' /etc/security/*
    [root@linux ~]# grep -r "limits the $A" /etc/security/*
    /etc/security/limits.conf:#        - core - limits the core file size (KB)

     

    - SecureCRT 처럼 색상 강조가 필요하다면 옵션을 넣으면 된다 (--color=auto)

    - 색상 강조 옵션은 출력 자체가 느리므로, 화면에 다량 출력을 해야 한다면 끄는걸 추천

    - 옵션을 키지 않았는데, 색상 강조 옵션이 들어가 있다면 OS 자체에 alias 가 걸려있을테니 아래와 같이 조치함

    [root@linux ~]# type grep
    grep is aliased to `grep --color=auto'
    [root@linux ~]# alias
    alias cp='cp -i'
    alias egrep='egrep --color=auto'
    alias fgrep='fgrep --color=auto'
    alias grep='grep --color=auto'
    alias l.='ls -d .* --color=auto'
    alias ll='ls -l --color=auto'
    alias ls='ls --color=auto'
    alias mv='mv -i'
    alias rm='rm -i'
    alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
    [root@linux ~]# which grep
    alias grep='grep --color=auto'
            /bin/grep
    [root@linux ~]# /bin/grep PASS_MIN_LEN /etc/login.defs

    ▷ grep 명령어는 alias로 호출됨

    alias 조회시 grep --color=auto 로 호출됨

    따라서 명령어 입력을 alias가 아닌 grep 명령어를 직접 호출하면 됨. which 로 명령어 위치를 찾은 후 사용한다 (/bin/grep)

    원치 않을 경우 환경변수 파일을 수정해야 함 (이후 재접속 또는 source 명령)

     

    환경변수 파일에서 삭제)

    - /etc/profile.d/colorgrep.sh

    [root@linux ~]# cat /etc/profile.d/colorgrep.sh
    # color-grep initialization
    
    /usr/libexec/grepconf.sh -c || return
    
    alias grep='grep --color=auto' 2>/dev/null
    alias egrep='egrep --color=auto' 2>/dev/null
    alias fgrep='fgrep --color=auto' 2>/dev/null

    일시적 off)

    [root@linux ~]# type grep
    grep is aliased to `grep --color=auto'
    [root@linux ~]# unalias grep
    [root@linux ~]# type grep
    grep is hashed (/bin/grep)

     

     

    [메뉴얼 (manual)]

    GREP(1)                                                                       General Commands Manual                                                                      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 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, two variant programs egrep and fgrep are available.  egrep is the same as grep -E.  fgrep is the same as grep -F.  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, --fixed-regexp
                  Interpret  PATTERN  as  a  list  of  fixed strings, separated by newlines, any of which is to be matched.  (-F is specified by POSIX, --fixed-regexp is an obsoleted
                  alias, please do not use it in new scripts.)
    
           -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.  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 (described under --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 (described under --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 (described under --group-separator) between contiguous groups of matches.  With the
                  -o or --only-matching option, this has no effect and a warning is given.
    
           --group-separator=SEP
                  Use SEP as a group separator. By default SEP is double hyphen (--).
    
           --no-group-separator
                  Use empty string as a group separator.
    
       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, 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.  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,” “extended” and “perl.” 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.
           {,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.
    
       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 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 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 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.  Note, however, that POSIX only mandates, for programs such as grep, cmp, and diff, that the exit status in case  of  error  be  greater
           than 1; it is therefore advisable, for the sake of portability, to use logic that tests for this general condition instead of strict equality with 2.
    
    COPYRIGHT
           Copyright 1998-2000, 2002, 2005-2014 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  <bug-grep@gnu.org>,  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), 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, which you can read at http://www.gnu.org/software/grep/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
           This man page is maintained only fitfully; the full documentation is often more up-to-date.
    
           GNU's not Unix, but Unix is a beast; its plural form is Unixen.

     

     


    업데이트) 2023.12.20

    홈페이지) https://www.gnu.org/software/grep
    라이센스) 무료 (GNU GPL)

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