Modern grep

Update: I updated the post for ripgrep.

grep reigned as the preeminent text search tool for a long time. Yet grep’s overly unopinionated approach to defaults and maintaining backwards compatibility allowed new tools — namely; ack, the silver searcher, and ripgrep — to encroach on its territory.

grep is ubiquitous. Unix-like systems come with grep installed and you can install grep on Windows. I search with ripgrep on my computer because I can install it once and use its features day-to-day. But when I work on remote systems, it’s more efficient to search with grep. It’s worth knowing how to use grep and how to improve it.

With some grep know-how, we can make grep faster and behave like these modern search tools.

Exclude directories

grep can exclude directories that it searches, increasing its speed substantially. The following excludes the .git directory from the grep search:

$ grep --exclude-dir=.git

This arg speeds up searches by a lot, I ran two uncached searches in Rails’s repo:

$ grep -r "class << self" .
$ grep -rIPs --exclude-dir=.[a-zA-Z0-9]* --exclude=.* --exclude=*~ "class << self" .

The non-excluding grep took 6.009s. The excluding grep took 2.235s.

Perl regular expressions

Modern search tools like ack support the popular Perl regular expressions. By default, grep uses the less known POSIX regular expressions.

For example, let’s say we want to match a phone number and capture its area codes.

  • The Perl regular expression:

  • The POSIX regular expression:


Fortunately, you can use Perl regular expressions with grep by giving it the -P or --perl-regexp argument.

grep -P "(\d{3})-\d{3}-\d{4}"

Useful defaults

Having to give grep all these arguments would be a drag, to configure grep to exclude hidden directories and use Perl regular expressions by default, set the shell variable GREP_OPTIONS:

export GREP_OPTIONS='-rIPs --exclude-dir=.[a-zA-Z0-9]* --exclude=.* --exclude=*~ --color=auto'

Git grep

There’s no argument to make grep organize its output like ack. Also, neither integrates with git, but git has its own grep for searching your repos. You can read my post on searching git like a ninja to learn about git grep and get the best of both grep and ack.

Sources and further reading

  • why GNU grep is fast
  • History of grep (including Ken Thompson’s inspiration for the name: ed’s g/re/p — similar to the :g/re/p Vim user’s have today!)
  • you will need grep version >= 2.5.3 to use --exclude-dir