UNIX for Dummies Questions & Answers

How do you negate a literal hyphen/dash in a regex? If it's the first character inside the brackets, then it is read literally.

Code:

[-]

But if you stick a caret to the left of it, to negate it, then it seems it is no longer read literally. Or whatever, it doesn't work.

Code:

[^-]

Nor does escaping it seem to work.

Code:

[^\-]

I can't figure this out, and surprisingly, I couldn't come up with anything online. It seems most people are trying to accept hyphens in their regexes, but I am trying to eliminate hyphenated words from my results. No doubt I am missing something obvious and simple.

Not sure what OS, shell, etc., etc., that you're using, but is this what you're trying to do?

Code:

cat file 

one
two-three
four-five
six seven
eight

grep -v '\-' file 

one
six seven
eight

Actually this is as baffling for you as it is for me. I haven't noticed this behavior before. The GNU-sed i have at hand actually gets it right (see below).

What you can do is to "invert" the action tied to the regexp in question, for instance, using the following input file (no trailing blanks):

Code:

1 -
2
3
4
5
6 -
7
8
9
10

Code:

$ sed -n '/[-]/p' /path/to/input
1 -
6 -

would print all lines with hyphens in it. Instead of the non-working

Code:

sed -n '/[^-]/p' /path/to/input

one could use

Code:

$ sed -n '/[-]/!p' /path/to/input
2
3
4
5
7
8
9
10

which works as expected. I am aware that this is a work-around instead of a solution, but the best i can come up right now. Actually my sed got the regexp in question correct:

Code:

$ sed -n '/[^-]$/p' /path/to/input
2
3
4
5
7
8
9
10

I was first tricked by the regexp above, but it only searches for any non-hyphen and this condition is met by any line, even the ones with hyphens in them because they also have non-hyphens. When i anchored the non-hyphen to the end, i got the correct and expected result.

I hope this helps.

bakunin

Yes, that is precisely what I'm trying to do. Although, I am no longer trying, I am doing. Thank you.

God, the 'v' flag.... [head shaking]....