[plug] Grep not following my regex

Tim Bowden tim.bowden at westnet.com.au
Tue Sep 15 09:38:39 WST 2009

On Tue, 2009-09-15 at 09:11 +0800, Tim wrote:
> I have been doing some string extraction for an application I've
> written. I needed to extract a number (with decimal point) from a one
> line string. I had the grep working, but then having moved to another
> computer, it stopped working. I did some debugging on the computer I'd
> moved to, to see why my application no longer worked, and narrowed it
> down to this grep.
> egrep -o '[0-9.]*'
> By changing the grep to the following, I managed to get it working again.
> egrep -o '[0-9.]+'
> Now I know that the + may make more sense now, by forcing a match, but
> I can't see why the first regex stopped working.
> The string it's matching against is:
> You currently have 347.454MB remaining
> and obviously it just pulls out the 347.454.
> Other than bash stealing the * from the grep (which I am sure
> shouldn't be happening due to the quotes), can someone let me know why
> the first regex stopped working? (Also, I was moving from an Ubuntu
> system to a Fedora system)
> Thanks
> Tim

The '.' has special meaning in a regex.  Escape it to make it just a

Without looking at your problem in detail, here is a possible regex for
a decimal point number.

grep -o [0-9]+\.[0-9]+

Tim Bowden

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