awk - Variable expansion in regex

Question

Why doesn't something like this work:

echo 4 | awk --assign=abc=4 '/$abc/'

The actual example is much more complicated. Basically I have a regex I need repeated several times so I'm storing it in abc. Is there any way to expand an awk variable in /<regex>/? I've tried single and double quotes, every combination. I really need that line to be single quoted because I have several double quotes, it actually looks more like awk --assign=test=something '/$test/ { a lot of stuff here inc $test several times with double quotes; }'

anubhava · Accepted Answer · 2013-10-04 18:49:17Z

5

awk doesn't use variables between / and / regex:

Following equivalent will work with same effect using ~ regex operator:

echo 4 | awk --assign=abc=4 '$0 ~ abc'
4

answered Oct 4, 2013 at 18:49

anubhava

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5 Comments

Chris Seymour Over a year ago

It's strange seeing the long option used.

user2672807 Over a year ago

Thanks. I did some research in the gawk manual but I didn't see anything about no variables in //. @sudo_O yeah I tried long after short didn't work (I thought maybe there was a difference). I switched back to -v with the answer provided.

Chris Seymour Over a year ago

They is not difference, just in the 500+ awk questions I have answered I've never seen it used. I had to actually check the man myself!

glenn jackman Over a year ago

I find the gawk manual pretty hard to navigate. Nevertheless I found gnu.org/software/gawk/manual/html_node/… and gnu.org/software/gawk/manual/html_node/Computed-Regexps.html

anubhava Over a year ago

@glennjackman: Thanks for sharing that link (I couldn't trace that in my search).

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