Using a user-set variable in an awk command

Question

I'm trying to use awk with a user-defined variable ($EVENT, where $EVENT is a filename and also a column in a textfile) in the if condition, but it doesn't seem to recognize the variable. I've tried with various combinations of ', ", { and ( but nothing seem to work.

EVENT=19971010_1516.txt
awk '{if ($2=="$EVENT") print $3,$4,$8}' FILENAME.txt > output.txt

It is possible to use user-defined variables in awk commands? If so, how does the syntax work?

Answer 1

you cannot use $FOO directly in your code, because awk will think it is column FOO. (FOO is variable). but your FOO is empty. to use shell var, use -v like:

awk -v event="$EVENT" '{print event}' file

Answer 2

If you want to include the variable in the awk script literally then you need to enclose the script in double quotes (single quotes do not expand variables). So something like awk '{if ($2=="'"$EVENT"'") print $3,$4,$8}' FILENAME.txt > output.txt'. Which uses single quotes on the rest of the awk script to avoid needing to escape the $ characters but then uses double quotes for the event variable.

That being said you almost certainly want to expose the shell variable to awk as an awk variable which means you want to use the -v flag to awk. So something like awk -vevent="$EVENT" '{if ($2==event) print $3,$4,$8}' FILENAME.txt > output.txt. (Alternatively you could use something like awk '{if ($2==event) print $3,$4,$8}' event="$EVENT" FILENAME.txt > output.txt.)

You could also simplify your awk body a bit by using '$2 == event {print $3,$4,$8}' and let patterns do what they are supposed to do.

Answer 3

You can do:

awk '$2==event {print $3,$4,$8}' event="$EVENT" FILENAME.txt > output.txt

awk -v event="$EVENT" '$2==event {print $3,$4,$8}' FILENAME.txt > output.txt

See this post for more info: How do I use shell variables in an awk script?