concatenating variables and regexp in awk

[Michele (Mike) Alberton]

Hi Folks !

I was trying to find a way to use awk to extract patterns made of some regexp and a variable.

Basically I should invoke:

awk -v VALUE="whatever" -f *.awk xxx.dat

and I would like to extract for instance:

+whatever
whatever123
...
Do you know how to concatenate for instance
/\+?/ with a variable ?

Thanks !

Mike

[A. Clay Stephenson · Accepted solution]

Here is one approach:

awk -v VALUE="whatever" '{ if ($0 ~ VALUE) print $0 }' xxx.dat

That should work for your trivial example but if you need more powerful regular expressions then you might have to use a BEGIN { } section leveraging a sprintf to build up a variable for the subsequent match (~) operator within the main awk loop.

[Graham Cameron_1]

123 is easy.
Build up your regexp in the BEGIN clause.
The space operator concatenates 2 strings, so the following will print any line containing "whatever123":

awk -v VALUE=whatever '
BEGIN {yourregexp=VALUE "123"}
$0 ~ yourregexp {print}
' xxx.dat

+ is more difficult, because it has special meaning in an RE.
You could use index:

awk -v VALUE=whatever '
BEGIN {yourregexp="+" VALUE}
{if (index ($0, yourregexp) != 0) print }
' xxx.dat

- Graham

[Michele (Mike) Alberton]

Thank You guys, points well earned...

I love this Forum.

Cheers,

Mike