Wildcards for filepaths aren't working in grep

Question

I need to grep words like these:

ABC-DEF
AB2-DEF
AB3-DEF
AB-DEF

So I was trying:

grep AB*-DEF
grep -w -AB*-DEF
grep -w AB*DEF

But neither of them are working.

Solution 1

* in a regex is not like a filename glob. It means 0 or more of the previous character/pattern. So your examples would be looking for a A then 0 or more B then -DEF

. in regex means "any character" so you could fix your pattern by using

grep 'AB.*DEF'

Solution 2

As far as your patterns are concerned, this would be the safest to match only intended strings:

grep 'AB.\{0,1\}-DEF' file.txt

Or

grep -E 'AB.?-DEF' file.txt

. matches any single character, ? and \{0,1\} matches the previous token zero or one time, so in total .? and .\{0,1\}will match zero or one character before -DEF.

If you use AB.*-DEF or AB.*DEF, grep will greedily match unintended strings, for example:

ABCG-DEF
ABCGLHHJKH90-DEF

Solution 3

You can use:

grep 'AB.*-DEF' file.txt

Comments

[Stéphane Chazelas]

That command crashed my machine. I had a AB.\(a*\)\{10000\}-DEF file in the current directory.

[nghnam]

I edited my post, quoted the search pattern. Thank you.

[cuonglm]

@nghnam: Please take time to edit your answer here, too. Or deleting it, otherwise other people will be confused with the information in that answer.

[heemayl]

This will match many other patterns e.g. ABCGLHHJKH90-DEF

[Eric Renouf]

True heemayl, but it is in keeping with the filesystem glob expansion like Jeevan seemed to be trying for in the question.