Using a variable in awk command to name file

Question

I am splitting up a file with awk command, I want to name the file using a variable however I have not had much luck. Here is the line:

awk '/STX/ {f="$tp"++i;} {print > f}' $tp.mixed

this just creates files with $tp# as name.

I read the post "How to use shell variables in awk script" but was unable to figure out how to apply that to me question.

Possible duplicate of How to use shell variables in awk script — Etan Reisner
– Etan Reisner, Commented Oct 15, 2015 at 19:19
You don't expand the shell variable in the awk script. You use -v awkvar="$tp"`` to create an awk variable with the value you need and then use the variable awkvar` in the awk script. f=awkvar(++i) or similar. — Etan Reisner
– Etan Reisner, Commented Oct 15, 2015 at 19:23
awk -v tp="$tp" '/STX/ {if (f) close(f); f = tp (++i)} {print > f} END{if (f) close(f)}' $tp.mixed — anubhava
– anubhava, Commented Oct 15, 2015 at 19:40
Thank you anubhava!! that worked. Question, why do you have to have the if (f) close (f) and END{if (f) close(f)? thank you, trying to understand shell scripting and awk better. — Brian Duffy
– Brian Duffy, Commented Oct 15, 2015 at 19:44
@BrianDuffy There is a limit on the number of open files you can have. If you explicitly use close every time you are done with a file here, you will never reach that limit. — John1024
– John1024, Commented Oct 15, 2015 at 19:50

anubhava · Accepted Answer · 2015-10-15 22:28:59Z

3

You can use this awk command to pass variable from command line:

awk -v tp="$tp" '/STX/{close(f); f=tp (++i)} f{print > f} END{close(f)}' "$tp.mixed"

Also important is to close the files you're opening for writing output. By calling close we are avoiding memory leak due to large number of opened files.

edited Oct 15, 2015 at 22:28

answered Oct 15, 2015 at 20:28

anubhava

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Brian Duffy · Accepted Answer · 2015-10-15 20:28:22Z

0

anubhava answered my question in the comments:

awk -v tp="$tp" '/STX/ {if (f) close(f); f = tp (++i)} {print > f} END{if (f) close(f)}' $tp.mixed

works

thank you everyone for your help

answered Oct 15, 2015 at 20:28

Brian Duffy

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