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Top Forums Shell Programming and Scripting Understanding pattern matching used in a grep command Post 302605200 by alister on Tuesday 6th of March 2012 11:07:56 PM
Old 03-07-2012
Quote:
Originally Posted by agama
Placing -- ahead of the pattern is the defacto standard way to indicate end of command line flags. Most commands that expect dashed command line flags recognise the double dash with trailing whitespace to mean the end of the list and to assume the next token is the first positional parameter.

Using the [-]- obviously works, but makes the intent of the pattern less obvious.

I was going to quote the grep man page, but it makes no mention of this.
It's documented by POSIX in the Shell and Utilities volume, since it applies to many utilities. See the OPTIONS section of http://pubs.opengroup.org/onlinepubs...html#tag_17_04 for more info.

Of interest may be the fact that POSIX requires compliant echo implementations to NOT support the -- argument's semantics. http://pubs.opengroup.org/onlinepubs...ties/echo.html

This means that conformant echos cannot support any command options. Of course, in practice, most do implement some options and there's usually no way to disable the option processing. This renders the general case of echo $text problematic. If $text expands to a valid option, the result is something unintended.

This is why these days I use printf for most everything.

Regards,
Alister
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GIT-GREP(1)							    Git Manual							       GIT-GREP(1)

NAME
git-grep - Print lines matching a pattern SYNOPSIS
git grep [-a | --text] [-I] [-i | --ignore-case] [-w | --word-regexp] [-v | --invert-match] [-h|-H] [--full-name] [-E | --extended-regexp] [-G | --basic-regexp] [-P | --perl-regexp] [-F | --fixed-strings] [-n | --line-number] [-l | --files-with-matches] [-L | --files-without-match] [(-O | --open-files-in-pager) [<pager>]] [-z | --null] [-c | --count] [--all-match] [-q | --quiet] [--max-depth <depth>] [--color[=<when>] | --no-color] [--break] [--heading] [-p | --show-function] [-A <post-context>] [-B <pre-context>] [-C <context>] [-W | --function-context] [-f <file>] [-e] <pattern> [--and|--or|--not|(|)|-e <pattern>...] [ [--[no-]exclude-standard] [--cached | --no-index | --untracked] | <tree>...] [--] [<pathspec>...] DESCRIPTION
Look for specified patterns in the tracked files in the work tree, blobs registered in the index file, or blobs in given tree objects. Patterns are lists of one or more search expressions separated by newline characters. An empty string as search expression matches all lines. CONFIGURATION
grep.lineNumber If set to true, enable -n option by default. grep.patternType Set the default matching behavior. Using a value of basic, extended, fixed, or perl will enable the --basic-regexp, --extended-regexp, --fixed-strings, or --perl-regexp option accordingly, while the value default will return to the default matching behavior. grep.extendedRegexp If set to true, enable --extended-regexp option by default. This option is ignored when the grep.patternType option is set to a value other than default. OPTIONS
--cached Instead of searching tracked files in the working tree, search blobs registered in the index file. --no-index Search files in the current directory that is not managed by Git. --untracked In addition to searching in the tracked files in the working tree, search also in untracked files. --no-exclude-standard Also search in ignored files by not honoring the .gitignore mechanism. Only useful with --untracked. --exclude-standard Do not pay attention to ignored files specified via the .gitignore mechanism. Only useful when searching files in the current directory with --no-index. -a, --text Process binary files as if they were text. -i, --ignore-case Ignore case differences between the patterns and the files. -I Don't match the pattern in binary files. --max-depth <depth> For each <pathspec> given on command line, descend at most <depth> levels of directories. A negative value means no limit. This option is ignored if <pathspec> contains active wildcards. In other words if "a*" matches a directory named "a*", "*" is matched literally so --max-depth is still effective. -w, --word-regexp Match the pattern only at word boundary (either begin at the beginning of a line, or preceded by a non-word character; end at the end of a line or followed by a non-word character). -v, --invert-match Select non-matching lines. -h, -H By default, the command shows the filename for each match. -h option is used to suppress this output. -H is there for completeness and does not do anything except it overrides -h given earlier on the command line. --full-name When run from a subdirectory, the command usually outputs paths relative to the current directory. This option forces paths to be output relative to the project top directory. -E, --extended-regexp, -G, --basic-regexp Use POSIX extended/basic regexp for patterns. Default is to use basic regexp. -P, --perl-regexp Use Perl-compatible regexp for patterns. Requires libpcre to be compiled in. -F, --fixed-strings Use fixed strings for patterns (don't interpret pattern as a regex). -n, --line-number Prefix the line number to matching lines. -l, --files-with-matches, --name-only, -L, --files-without-match Instead of showing every matched line, show only the names of files that contain (or do not contain) matches. For better compatibility with git diff, --name-only is a synonym for --files-with-matches. -O [<pager>], --open-files-in-pager [<pager>] Open the matching files in the pager (not the output of grep). If the pager happens to be "less" or "vi", and the user specified only one pattern, the first file is positioned at the first match automatically. -z, --null Output instead of the character that normally follows a file name. -c, --count Instead of showing every matched line, show the number of lines that match. --color[=<when>] Show colored matches. The value must be always (the default), never, or auto. --no-color Turn off match highlighting, even when the configuration file gives the default to color output. Same as --color=never. --break Print an empty line between matches from different files. --heading Show the filename above the matches in that file instead of at the start of each shown line. -p, --show-function Show the preceding line that contains the function name of the match, unless the matching line is a function name itself. The name is determined in the same way as git diff works out patch hunk headers (see Defining a custom hunk-header in gitattributes(5)). -<num>, -C <num>, --context <num> Show <num> leading and trailing lines, and place a line containing -- between contiguous groups of matches. -A <num>, --after-context <num> Show <num> trailing lines, and place a line containing -- between contiguous groups of matches. -B <num>, --before-context <num> Show <num> leading lines, and place a line containing -- between contiguous groups of matches. -W, --function-context Show the surrounding text from the previous line containing a function name up to the one before the next function name, effectively showing the whole function in which the match was found. -f <file> Read patterns from <file>, one per line. -e The next parameter is the pattern. This option has to be used for patterns starting with - and should be used in scripts passing user input to grep. Multiple patterns are combined by or. --and, --or, --not, ( ... ) Specify how multiple patterns are combined using Boolean expressions. --or is the default operator. --and has higher precedence than --or. -e has to be used for all patterns. --all-match When giving multiple pattern expressions combined with --or, this flag is specified to limit the match to files that have lines to match all of them. -q, --quiet Do not output matched lines; instead, exit with status 0 when there is a match and with non-zero status when there isn't. <tree>... Instead of searching tracked files in the working tree, search blobs in the given trees. -- Signals the end of options; the rest of the parameters are <pathspec> limiters. <pathspec>... If given, limit the search to paths matching at least one pattern. Both leading paths match and glob(7) patterns are supported. EXAMPLES
git grep 'time_t' -- '*.[ch]' Looks for time_t in all tracked .c and .h files in the working directory and its subdirectories. git grep -e '#define' --and ( -e MAX_PATH -e PATH_MAX ) Looks for a line that has #define and either MAX_PATH or PATH_MAX. git grep --all-match -e NODE -e Unexpected Looks for a line that has NODE or Unexpected in files that have lines that match both. GIT
Part of the git(1) suite Git 1.8.3.1 06/10/2014 GIT-GREP(1)
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