CODEWITHSUNDEEP
macosgrep
andros
andros

Reputation: 153

Reading grep patterns from a file with '-x' (exact line match) ... does pattern order matter?

New to using grep, and having a weird issue that's got me stumped. I created two identical files:

test1.txt

foo
foo bar

test2.txt

foo
foo bar

When I run grep -x -f test1.txt test2.txt, I expect to get foo and foo bar, but all I get is foo. But then, if I switch the order of the patterns in test1.txt as follows:

test1.txt

foo bar
foo

Now, when I run grep -x -f test1.txt test2.txt, I get what I want: foo and foo bar. Why? :( Also, is there a way to make this work without re-arranging the order of the patterns? (This is part of a larger project, and there are many examples of this.) Thank you!

Upvotes: 3

Views: 1118

Answers (1)

Michal Gasek
Michal Gasek

Reputation: 6413

Mac OSX with grep (BSD grep) 2.5.1-FreeBSD

It looks like a bug in BSD grep, here is a related topic also: grep (BSD grep) 2.5.1-FreeBSD on mac os 10.8 line regexp mode not working with overlapping patterns

I have the same version of grep (grep (BSD grep) 2.5.1-FreeBSD) on my Mac OSX 10.9.1 and it behaves exactly the same.

Ubuntu Precise with GNU grep

Works as expected.

vagrant@precise64:~$ grep -V
grep (GNU grep) 2.10
(...details removed...)
vagrant@precise64:~$ echo -e 'foo\nfoo bar' > test1.txt && cp test1.txt test2.txt
vagrant@precise64:~$ grep -x -f test1.txt test2.txt
foo
foo bar

Mac OSX with GNU grep

Works as expected.

$ ggrep -V
ggrep (GNU grep) 2.14.56-1e3d
(...details removed...)
$ ggrep -x -f test1.txt test2.txt
foo
foo bar

Sulution #1:

If you really have to use BSD grep on Mac OSX, here is something that actually works:

$ grep -V
grep (BSD grep) 2.5.1-FreeBSD
$ grep -e "^foo$" -e "^foo bar$" test2.txt
foo
foo bar

Sulution #2:

Install GNU grep via homebrew:

$ brew tap homebrew/dupes
Cloning into '/usr/local/Library/Taps/homebrew-dupes'...
remote: Reusing existing pack: 1083, done.
remote: Counting objects: 9, done.
remote: Compressing objects: 100% (7/7), done.
remote: Total 1092 (delta 3), reused 8 (delta 2)
Receiving objects: 100% (1092/1092), 216.09 KiB | 278.00 KiB/s, done.
Resolving deltas: 100% (559/559), done.
Checking connectivity... done
Tapped 39 formula
$ brew install grep
(...installing...)
usr/local/Cellar/grep/2.15: 13 files, 872K, built in 40 seconds

It will be installed as ggrep this way. There are ways to install as grep also, or replace system grep, I wouldn't do that though (this is offtopic). Anyway after installing:

$ which ggrep
/usr/local/bin/ggrep

Upvotes: 3

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