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Linux/Unix Command: grep - Search within files

grep - Search Within Files

CODE:

$ grep [options] [pattern] [file]

The mv command changes the current directory, and is used to move or browse directories/folders on your server via SSH.

For example:

CODE:

$ grep needle haystack.txt

This would print (show) all lines in haystack.txt containing "needle", by default grep is case sensitive so it will not match lines with "Needle", also it doesn't consider words so it will match "needle", "needles", "asdfgneedle" etc.

CODE:

$ grep -i needle haystack.txt

Using the "-i" option makes the grep command case INSENSTIVE so it will match "needle", "Needle" and also "needles" etc.

CODE:

$ grep -w needle haystack.txt

Using the "-w" option makes the grep command word aware so it only matches "needle" when it appears as "needle" and not when it appears as "needles" or "aaaaaneedles" etc.

Note: There are 2 other programs, egrep and fgrep, egrep is the same as grep -E and 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.

-a, --text

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

-B NUM, --before-context=NUM

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

-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 isbinary, andgrep normally outputs either a one-line message saying that a binary file matches, or no message if there is no match. If TYPE iswithout-match, grep assumes that a binary file does not match; this is equivalent to the-I option. If TYPE istext, 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.

--colour[=WHEN],--color[=WHEN]

Surround the matching string with the marker find inGREP_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 isread, which means that devices are read just as if they were ordinary files. If ACTION isskip, devices are silently skipped.

-d ACTION, --directories=ACTION

If an input file is a directory, use ACTION to process it. By default, ACTION isread, which means that directories are read just as if they were ordinary files. If ACTION isskip, directories are silently skipped. If ACTION isrecurse, 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. Whengrep 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 thanNUM. When the-v or--invert-match option is also used, grep stops after outputtingNUM non-matching lines.

--mmap

If possible, use the mmap system call to read input, instead of the default read system call. In some situations, --mmap yields better performance. However, --mmap can cause undefined behavior (including core dumps) if an input file shrinks whilegrep is operating, 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 --label=foo something

--line-buffering

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-messagesoption.

-R, -r, --recursive

Read all files under each directory, recursively; this is equivalent to the-d recurseoption.

--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 GNUgrep, traditionalgrep did not conform to POSIX.2, because traditionalgrep lacked a-q option and its-s option behaved like GNUgrep's -q option. Shell scripts intended to be portable to traditionalgrep 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. Ifgrepdecides 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 causesgrep 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 runninggrep 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 ofgrep 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 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.

-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.