grep
Linux Command – grep ใช้ในการค้นหาบรรทัดใน file ที่ตรงเงื่อนไข
คำสั่ง
จากตัวอย่าง file test1
$ cat test1 Ant Bee Cat Dog Fly
1. ค้นหาบรรทัดที่มี text ตรงเงือนไข
grep <text> <file>
$ grep a test1 Cat Man $ grep an test1 Man
2. ค้นหาบรรทัดที่มี text ตรงเงื่อนไข โดยไม่สนใจตัวเล็กตัวใหญ่
grep -i <text> <file>
$ grep -i "a" test1 Ant Cat Man
3. ค้นหาบรรทัดที่ไม่มี text ตามเงื่อนไข
grep -v <text> <file>
$ grep -vi "a" test1 Ant Bee Dog Fly
โครงสร้างคำสั่ง
grep [OPTIONS] PATTERN [FILE...]
grep [OPTIONS] [-e PATTERN]... [-f FILE]... [FILE...]
รายละเอียด
เป็นคำสั่งที่ใช้ค้นหาบรรทัดใน file ที่ตรงเงื่อนไข มีการนำไปพัฒนาต่อยอดเพื่อให้สามารถทำงานกับ expression ที่ซับซ้อนยิ่งขึ้น เช่น egrep, fgrep, pgrep
Option
--help Output a usage message and exit. -V, --version Output the version number of grep and exit. Matcher Selection -E, --extended-regexp Interpret PATTERN as an extended regular expression (ERE, see below). -F, --fixed-strings Interpret PATTERN as a list of fixed strings (instead of regular expressions), separated by newlines, any of which is to be matched. -G, --basic-regexp Interpret PATTERN as a basic regular expression (BRE, see below). This is the default. -P, --perl-regexp Interpret the pattern as a Perl-compatible regular expression (PCRE). This is highly experimental and grep -P may warn of unimplemented features. Matching Control -e PATTERN, --regexp=PATTERN Use PATTERN as the pattern. If this option is used multiple times or is combined with the -f (--file) option, search for all patterns given. This option can be used to protect a pattern beginning with “-”. -f FILE, --file=FILE Obtain patterns from FILE, one per line. If this option is used multiple times or is combined with the -e (--regexp) option, search for all patterns given. The empty file contains zero patterns, and therefore matches nothing. -i, --ignore-case Ignore case distinctions in both the PATTERN and the input files. -v, --invert-match Invert the sense of matching, to select non-matching lines. -w, --word-regexp Select only those lines containing matches that form whole words. The test is that the matching substring must either be at the beginning of the line, or preceded by a non- word constituent character. Similarly, it must be either at the end of the line or followed by a non-word constituent character. Word-constituent characters are letters, digits, and the underscore. -x, --line-regexp Select only those matches that exactly match the whole line. For a regular expression pattern, this is like parenthesizing the pattern and then surrounding it with ^ and $. -y Obsolete synonym for -i. General Output Control -c, --count Suppress normal output; instead print a count of matching lines for each input file. With the -v, --invert-match option (see below), count non-matching lines. --color[=WHEN], --colour[=WHEN] Surround the matched (non-empty) strings, matching lines, context lines, file names, line numbers, byte offsets, and separators (for fields and groups of context lines) with escape sequences to display them in color on the terminal. The colors are defined by the environment variable GREP_COLORS. The deprecated environment variable GREP_COLOR is still supported, but its setting does not have priority. WHEN is never, always, or auto. -L, --files-without-match Suppress normal output; instead print the name of each input file from which no output would normally have been printed. The scanning will stop on the first match. -l, --files-with-matches Suppress normal output; instead print the name of each input file from which output would normally have been printed. The scanning will stop on the first match. -m NUM, --max-count=NUM Stop reading a file after NUM matching lines. If the input is standard input from a regular file, and NUM matching lines are output, grep ensures that the standard input is positioned to just after the last matching line before exiting, regardless of the presence of trailing context lines. This enables a calling process to resume a search. When grep stops after NUM matching lines, it outputs any trailing context lines. When the -c or --count option is also used, grep does not output a count greater than NUM. When the -v or --invert-match option is also used, grep stops after outputting NUM non-matching lines. -o, --only-matching Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line. -q, --quiet, --silent Quiet; do not write anything to standard output. Exit immediately with zero status if any match is found, even if an error was detected. Also see the -s or --no-messages option. -s, --no-messages Suppress error messages about nonexistent or unreadable files. Output Line Prefix Control -b, --byte-offset Print the 0-based byte offset within the input file before each line of output. If -o (--only-matching) is specified, print the offset of the matching part itself. -H, --with-filename Print the file name for each match. This is the default when there is more than one file to search. -h, --no-filename Suppress the prefixing of file names on output. This is the default when there is only one file (or only standard input) to search. --label=LABEL Display input actually coming from standard input as input coming from file LABEL. This is especially useful when implementing tools like zgrep, e.g., gzip -cd foo.gz | grep --label=foo -H something. See also the -H option. -n, --line-number Prefix each line of output with the 1-based line number within its input file. -T, --initial-tab Make sure that the first character of actual line content lies on a tab stop, so that the alignment of tabs looks normal. This is useful with options that prefix their output to the actual content: -H,-n, and -b. In order to improve the probability that lines from a single file will all start at the same column, this also causes the line number and byte offset (if present) to be printed in a minimum size field width. -u, --unix-byte-offsets Report Unix-style byte offsets. This switch causes grep to report byte offsets as if the file were a Unix-style text file, i.e., with CR characters stripped off. This will produce results identical to running grep on a Unix machine. This option has no effect unless -b option is also used; it has no effect on platforms other than MS-DOS and MS-Windows. -Z, --null Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name. For example, grep -lZ outputs a zero byte after each file name instead of the usual newline. This option makes the output unambiguous, even in the presence of file names containing unusual characters like newlines. This option can be used with commands like find -print0, perl -0, sort -z, and xargs -0 to process arbitrary file names, even those that contain newline characters. Context Line Control -A NUM, --after-context=NUM Print NUM lines of trailing context after matching lines. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given. -B NUM, --before-context=NUM Print NUM lines of leading context before matching lines. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given. -C NUM, -NUM, --context=NUM Print NUM lines of output context. Places a line containing a group separator (--) between contiguous groups of matches. With the -o or --only-matching option, this has no effect and a warning is given. File and Directory Selection -a, --text Process a binary file as if it were text; this is equivalent to the --binary-files=text option. --binary-files=TYPE If the first few bytes of a file indicate that the file contains binary data, assume that the file is of type TYPE. By default, TYPE is binary, and grep normally outputs either a one-line message saying that a binary file matches, or no message if there is no match. If TYPE is without-match, grep assumes that a binary file does not match; this is equivalent to the -I option. If TYPE is text, grep processes a binary file as if it were text; this is equivalent to the -a option. When processing binary data, grep may treat non-text bytes as line terminators; for example, the pattern '.' (period) might not match a null byte, as the null byte might be treated as a line terminator. Warning: grep --binary-files=text might output binary garbage, which can have nasty side effects if the output is a terminal and if the terminal driver interprets some of it as commands. -D ACTION, --devices=ACTION If an input file is a device, FIFO or socket, use ACTION to process it. By default, ACTION is read, which means that devices are read just as if they were ordinary files. If ACTION is skip, devices are silently skipped. -d ACTION, --directories=ACTION If an input file is a directory, use ACTION to process it. By default, ACTION is read, i.e., read directories just as if they were ordinary files. If ACTION is skip, silently skip directories. If ACTION is recurse, read all files under each directory, recursively, following symbolic links only if they are on the command line. This is equivalent to the -r option. --exclude=GLOB Skip files whose base name matches GLOB (using wildcard matching). A file-name glob can use *, ?, and [...] as wildcards, and \ to quote a wildcard or backslash character literally. --exclude-from=FILE Skip files whose base name matches any of the file-name globs read from FILE (using wildcard matching as described under --exclude). --exclude-dir=DIR Exclude directories matching the pattern DIR from recursive searches. -I Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option. --include=GLOB Search only files whose base name matches GLOB (using wildcard matching as described under --exclude). -r, --recursive Read all files under each directory, recursively, following symbolic links only if they are on the command line. Note that if no file operand is given, grep searches the working directory. This is equivalent to the -d recurse option. -R, --dereference-recursive Read all files under each directory, recursively. Follow all symbolic links, unlike -r. Other Options --line-buffered Use line buffering on output. This can cause a performance penalty. -U, --binary Treat the file(s) as binary. By default, under MS-DOS and MS-Windows, grep guesses the file type by looking at the contents of the first 32KB read from the file. If grep decides the file is a text file, it strips the CR characters from the original file contents (to make regular expressions with ^ and $ work correctly). Specifying -U overrules this guesswork, causing all files to be read and passed to the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the end of each line, this will cause some regular expressions to fail. This option has no effect on platforms other than MS-DOS and MS-Windows. -z, --null-data Treat the input as a set of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline. Like the -Z or --null option, this option can be used with commands like sort -z to process arbitrary file names.
กลุ่มคำสั่ง
egrep, fgrep, pgrep, 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)
Reference:
Author: Suphakit Annoppornchai
Credit: https://saixiii.com
