grep and/or sed question

[Jeff Picton]

Hello all

Can anyone tell me how I may grep or use sed to obtain the FIRST instance of a regular expression within a file ?

Jeff

[Elmar P. Kolkman · Accepted solution]

Simplest way: grep | head -1

A lot of other solutions would work of course.

[Mark Grant]

Can we do perl?

perl -n -e 'if(/My Expression/){print;exit}' filename

[Mark Grant]

or awk if you like

awk 'match($0,"expression") > 0 {print;exit}
{next}' filename

I think, on large files, you would benefit from actually exiting when finding the first instance but maybe not.

[Dietmar Konermann]

Hmm... what avout this one?

sed -e '/My Expression/q;d'

Best regards...
Dietmar.

[Dietmar Konermann]

Just saw that the bunny went to the grep/head solution, although that this is a really bad approach. Consider a file, several MBs large. Even if is there is a hit in the 1st line, grep will scan it completetly. You should not do that. :-)

Best regards...
Dietmar.

[Jeff Picton]

Hi

Fortunately this log file is not large so the grep / head solution was fine for this purpose. Also the sed/awk solutions are fine but this is a shell script so didn't try the perl one.

Many Thanks

Jeff

[Mark Grant]

Hi Jeff,

Just for information, you can actually put the perl line in a shell script as it's a one liner and therefore much like putting awk or sed in your script.

On the other hand, it won't work too well if you don't actually have perl installed :)