32.4 Searching with Grep under Emacs

Just as you can run a compiler from Emacs and then visit the lines with compilation errors, you can also run grep and then visit the lines on which matches were found. This works by treating the matches reported by grep as if they were “errors.” The buffer of matches uses Grep mode, which is a variant of Compilation mode (see section Compilation Mode).

M-x grep

M-x lgrep

Run grep asynchronously under Emacs, with matching lines listed in the buffer named ‘*grep*’.

M-x grep-find

M-x find-grep

M-x rgrep

Run grep via find, with user-specified arguments, and collect output in the buffer named ‘*grep*’.

M-x kill-grep

Kill the running grep subprocess.

To run grep, type M-x grep, then enter a command line that specifies how to run grep. Use the same arguments you would give grep when running it normally: a grep-style regexp (usually in single-quotes to quote the shell's special characters) followed by file names, which may use wildcards. If you specify a prefix argument for M-x grep, it finds the tag (see section Tags Tables) in the buffer around point, and puts that into the default grep command.

Your command need not simply run grep; you can use any shell command that produces output in the same format. For instance, you can chain grep commands, like this:

grep -nH -e foo *.el | grep bar | grep toto

The output from grep goes in the ‘*grep*’ buffer. You can find the corresponding lines in the original files using C-x `, <RET>, and so forth, just like compilation errors.

Some grep programs accept a ‘--color’ option to output special markers around matches for the purpose of highlighting. You can make use of this feature by setting grep-highlight-matches to t. When displaying a match in the source buffer, the exact match will be highlighted, instead of the entire source line.

The command M-x grep-find (also available as M-x find-grep) is similar to M-x grep, but it supplies a different initial default for the command—one that runs both find and grep, so as to search every file in a directory tree. See also the find-grep-dired command, in Dired and find.

The commands M-x lgrep (local grep) and M-x rgrep (recursive grep) are more user-friendly versions of grep and grep-find, which prompt separately for the regular expression to match, the files to search, and the base directory for the search. Case sensitivity of the search is controlled by the current value of case-fold-search.

These commands build the shell commands based on the variables grep-template (for lgrep) and grep-find-template (for rgrep).

The files to search can use aliases defined in the variable grep-files-aliases.

Subdirectories listed in the variable grep-find-ignored-directories such as those typically used by various version control systems, like CVS and arch, are automatically skipped by rgrep.