BASH Regular expressions

scwxx77

I trying to do exercise 25.2 from 'UNIX and Linux System Administration Handbook' but I'm having trouble with the regular expression.

E25.2 Write a shell command line or script to parse the output of xdpyinfo and print the current screen resolution in the format XxY, e.g., 1024X768.

$ xdpyinfo | grep -i dimensions #returns the following:
    dimensions:     1208x960 pixels (338x253 millimeters)
$ xdpyinfo | grep -i dimensions | sed -n 's/\([0-9]+[x][0-9]+\)/\1/p'  # returns nothing

It's driving me nuts. Does anyone know where I'm going wrong?

dodgy

Yes, the first place I'd come to solve regex problems on *nix would be the road/cake stop subsection on a cycling forum.

sungod

take the easy way out...

xdpyinfo | grep -i dimensions | cut -d' ' -f7

dodgy

Anyway, think you've already solved it really? Yes you have additional data (in mm), but you still have answered the question.

jim453

scwxx77 wrote:

I trying to do exercise 25.2 from 'UNIX and Linux System Administration Handbook'

Don't.

chrisaonabike

Stackoverflow is what you want.

scwxx77

Awesome, sungod.

I'd still like to know why my answer returns nothing though. I'd really rather not register to another forum when there are obviously knowledgeable people on here.

sungod

afaik use of + to denote one or more of the preceding character isn't in all implementations

using [0-9][0-9]* is more reliable to match one or more decimal digits

tbh i find sed a pain, i rarely used it in 25+ years of scripting, preferred awk

if you really want to use sed, this should work...

xdpyinfo | sed -n 's/[ ]*dimensions[^0-9]*\([0-9][0-9]*x[0-9][0-9]*\).*/\1/p'

method: match/discard the initial non-numerics, match the wanted bit and stash it in 1, match/discard the unwanted remainder

scwxx77

Excellent, I'll sleep better tonight! Thanks.

desweller

Pour petrol on the keyboard and fling a lit match on it. These computers need a bit of teaching.

pinno

Can you use Delphi to help construct it?