Default grep options

When you’re searching a set of version-controlled files for a string with grep, particularly if it’s a recursive search, it can get very annoying to be presented with swathes of results from the internals of the hidden version control directories like .svn or .git, or include metadata you’re unlikely to have wanted in files like .gitmodules.

GNU grep uses an environment variable named GREP_OPTIONS to define a set of options that are always applied to every call to grep. This comes in handy when exported in your .bashrc file to set a “standard” grep environment for your interactive shell. Here’s an example of a definition of GREP_OPTIONS that excludes a lot of patterns which you’d very rarely if ever want to search with grep:

for pattern in .cvs .git .hg .svn; do
    GREP_OPTIONS="$GREP_OPTIONS --exclude-dir=$pattern

Note that --exclude-dir is a relatively recent addition to the options for GNU grep, but it should only be missing on very legacy GNU/Linux machines by now. If you want to keep your .bashrc file compatible, you could apply a little extra hackery to make sure the option is available before you set it up to be used:

if grep --help | grep -- --exclude-dir &>/dev/null; then
    for pattern in .cvs .git .hg .svn; do
        GREP_OPTIONS="$GREP_OPTIONS --exclude-dir=$pattern"

Similarly, you can ignore single files with --exclude. There’s also --exclude-from=FILE if your list of excluded patterns starts getting too long.

Other useful options available in GNU grep that you might wish to add to this environment variable include:

  • --color — On appropriate terminal types, highlight the pattern matches in output, among other color changes that make results more readable
  • -s — Suppresses error messages about files not existing or being unreadable; helps if you find this behaviour more annoying than useful.
  • -E, -F, or -P — Pick a favourite “mode” for grep; devotees of PCRE may find adding -P for grep‘s experimental PCRE support makes grep behave in a much more pleasing way, even though it’s described in the manual as being experimental and incomplete

If you don’t want to use GREP_OPTIONS, you could instead simply set up an alias:

alias grep='grep --exclude-dir=.git'

You may actually prefer this method as it’s essentially functionally equivalent, but if you do it this way, when you want to call grep without your standard set of options, you only have to prepend a backslash to its call:

$ \grep pattern file

Commenter Andy Pearce also points out that using this method can avoid some build problems where GREP_OPTIONS would interfere.

Of course, you could solve a lot of these problems simply by using ack … but that’s another post.

Vim as Debian default

The default text editor in installations of Debian and its derivatives is Nano, largely because it’s a simple and small editor. If you’re a Vim user, you might find it a little jarring to be presented with a modeless editor when you run commands like visudo or vipw.

Debian’s alternatives system makes this reasonably easy to adjust. If you have Vim installed, it should be available as one of the possible implementations of the editor alternative. You can check this with the update-alternatives command:

# update-alternatives --list editor

This shows that Vim is available as an alternative with /usr/bin/vim.basic, so you can update the symlink structure that defines the default editor like so:

# update-alternatives --set editor /usr/bin/vim.basic
... using /usr/bin/vim.basic to provide /usr/bin/editor (editor) in manual mode.

Now if you fire up visudo, vipw, or sudo -e you should find that Vim is fired up instead of the editor you didn’t want.

On my own workstation I have the latest Vim compiled from Mercurial and installed into /usr/local via checkinstall, so I had to add this to the alternatives system before I could use it:

# update-alternatives --install /usr/bin/editor editor /usr/local/bin/vim 200 \
    --slave /usr/share/man/man1/editor.1.gz editor.1.gz /usr/local/share/man/man1/vim.1.gz
# update-alternatives --set editor /usr/local/bin/vim
... using /usr/bin/vim.basic to provide /usr/bin/editor (editor) in manual mode.

Other relevant alternatives include the vi implementation for your system, which of course may not necessarily be Vim; some operating systems install the smaller and more vi-faithful nvi.