Why is grep -o -w not giving me the expected output on Mac OS X?

Question

If I do echo foo bar baz | grep -o -w baz the output is foo bar baz (and an extra newline).
The expected output would be baz as the -o option should only display the matched part.
I'm using Mac OS X 10.7.1 and the grep version is grep (GNU grep) 2.5.1

Answer 1

There's a workaround by using the grep regex syntax for matching the empty string at the beginning and end of a word!

# grep regex syntax for matching words only
man grep | less -p '\<'

# POSIX 1003.2 regular expression syntax for matching words only
# should work for sed, ed, ...
man re_format | less -p '\[\[:<:\]\]'

echo 'foo bar baz' | egrep -o '\<baz\>'

echo 'foo bar baz' | sed -n '/.*[[:<:]]\(baz\)[[:>:]].*/s//\1/p'

If you insist on using grep's -w flag, try the precompiled Rudix 2010 grep binary (grep-2.5.4-1.dmg).

http://rudix.org/packages-ghi.html#grep

Answer 2

Seems like a bug to me. If you don't mind using the grep from macports (v 2.9), it behaves the way you expect.

2.5.1 seems is far from the latest release, but I suppose you could try filling a bug with Apple.

Answer 3

Alternatively you could get install the latest GNU grep via homebrew e.g.

ruby -e "$(curl -fsSkL raw.github.com/mxcl/homebrew/go)"
brew tap homebrew/dupes/
brew install homebrew/dupes/grep

The do the following:

echo foo bar baz | /usr/local/bin/grep -o -w baz