grep command
linux의 grep은 파일 또는 표준 입력(Standard input)에 대해서 특정 패턴을 통해 검색 해주는 명령어 입니다.
패턴에 대해서는 기본값으로 기본 정규 표현식(basic regular expression - BRE)을 지원 합니다.
기본적인 사용 법은 다음과 같습니다.
$> grep
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.
$> grep Error /var/log/syslog
Aug 3 10:20:25 geeksaga org.a11y.Bus[4449]: ** (process:4467): WARNING **: Failed to register client: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SessionManager was not provided by any .service files
Aug 3 10:20:25 geeksaga org.freedesktop.systemd1[4449]: ** (process:4476): WARNING **: cgmanager method call org.linuxcontainers.cgmanager0_0.MovePidAbs failed: GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: invalid request. Use G_DBUS_DEBUG=message for more info.
...
표준 입력(Standard input)을 이용한 방법
$> dmesg | grep random
[ 0.000000] random: get_random_bytes called from start_kernel+0x99/0x51e with crng_init=0
[ 1.035100] random: systemd-udevd: uninitialized urandom read (16 bytes read)
[ 1.035156] random: systemd-udevd: uninitialized urandom read (16 bytes read)
[ 1.035164] random: systemd-udevd: uninitialized urandom read (16 bytes read)
[ 1.991103] random: fast init done
[ 45.515726] random: crng init done
[ 45.515727] random: 7 urandom warning(s) missed due to ratelimiting
help grep
$> grep --help
Usage: grep [OPTION]... PATTERN [FILE]...
Search for PATTERN in each FILE or standard input.
PATTERN is, by default, a basic regular expression (BRE).
Example: grep -i 'hello world' menu.h main.c
Regexp selection and interpretation:
-E, --extended-regexp PATTERN is an extended regular expression (ERE)
-F, --fixed-strings PATTERN is a set of newline-separated strings
-G, --basic-regexp PATTERN is a basic regular expression (BRE)
-P, --perl-regexp PATTERN is a Perl regular expression
-e, --regexp=PATTERN use PATTERN for matching
-f, --file=FILE obtain PATTERN from FILE
-i, --ignore-case ignore case distinctions
-w, --word-regexp force PATTERN to match only whole words
-x, --line-regexp force PATTERN to match only whole lines
-z, --null-data a data line ends in 0 byte, not newline
Miscellaneous:
-s, --no-messages suppress error messages
-v, --invert-match select non-matching lines
-V, --version display version information and exit
--help display this help text and exit
Output control:
-m, --max-count=NUM stop after NUM matches
-b, --byte-offset print the byte offset with output lines
-n, --line-number print line number with output lines
--line-buffered flush output on every line
-H, --with-filename print the file name for each match
-h, --no-filename suppress the file name prefix on output
--label=LABEL use LABEL as the standard input file name prefix
-o, --only-matching show only the part of a line matching PATTERN
-q, --quiet, --silent suppress all normal output
--binary-files=TYPE assume that binary files are TYPE;
TYPE is 'binary', 'text', or 'without-match'
-a, --text equivalent to --binary-files=text
-I equivalent to --binary-files=without-match
-d, --directories=ACTION how to handle directories;
ACTION is 'read', 'recurse', or 'skip'
-D, --devices=ACTION how to handle devices, FIFOs and sockets;
ACTION is 'read' or 'skip'
-r, --recursive like --directories=recurse
-R, --dereference-recursive likewise, but follow all symlinks
--include=FILE_PATTERN search only files that match FILE_PATTERN
--exclude=FILE_PATTERN skip files and directories matching FILE_PATTERN
--exclude-from=FILE skip files matching any file pattern from FILE
--exclude-dir=PATTERN directories that match PATTERN will be skipped.
-L, --files-without-match print only names of FILEs containing no match
-l, --files-with-matches print only names of FILEs containing matches
-c, --count print only a count of matching lines per FILE
-T, --initial-tab make tabs line up (if needed)
-Z, --null print 0 byte after FILE name
Context control:
-B, --before-context=NUM print NUM lines of leading context
-A, --after-context=NUM print NUM lines of trailing context
-C, --context=NUM print NUM lines of output context
-NUM same as --context=NUM
--color[=WHEN],
--colour[=WHEN] use markers to highlight the matching strings;
WHEN is 'always', 'never', or 'auto'
-U, --binary do not strip CR characters at EOL (MSDOS/Windows)
-u, --unix-byte-offsets report offsets as if CRs were not there
(MSDOS/Windows)
'egrep' means 'grep -E'. 'fgrep' means 'grep -F'.
Direct invocation as either 'egrep' or 'fgrep' is deprecated.
When FILE is -, read standard input. With no FILE, read . if a command-line
-r is given, - otherwise. If fewer than two FILEs are given, assume -h.
Exit status is 0 if any line is selected, 1 otherwise;
if any error occurs and -q is not given, the exit status is 2.
Report bugs to: bug-grep@gnu.org
GNU grep home page: <http://www.gnu.org/software/grep/>
General help using GNU software: <http://www.gnu.org/gethelp/>
tldr grep
$> tldr grep
grep
Matches patterns in input text.
Supports simple patterns and regular expressions.
- Search for an exact string:
grep search_string path/to/file
- Search in case-insensitive mode:
grep -i search_string path/to/file
- Search recursively (ignoring non-text files) in current directory for an exact string:
grep -RI search_string .
- Use extended regular expressions (supporting ?, +, {}, () and |):
grep -E ^regex$ path/to/file
- Print 3 lines of [C]ontext around, [B]efore, or [A]fter each match:
grep -C|B|A 3 search_string path/to/file
- Print file name with the corresponding line number for each match:
grep -Hn search_string path/to/file
- Use the standard input instead of a file:
cat path/to/file | grep search_string
- Invert match for excluding specific strings:
grep -v search_string
