pass & retrieve variables from awk

sharathkv25 · 02-16-2007, 12:32 AM

Code:

#myvar.ks

VAR=6
echo "test" | awk '{ print '$VAR' }'
echo "test" | awk '{ '$VAR'=7 }'
echo 'Assign='$VAR

Code:

$ ./myvar.ks
6
 syntax error The source line is 1.
 The error context is
                { >>>  6= <<< 7 }
 awk: The statement cannot be correctly parsed.
 The source line is 1.
Assign=6
$

Does any one know how I can assign a value to a shell variable from AWK?

Thanks

matthewg42 · 02-16-2007, 01:24 AM

In awk, you can access variable which have been exported to the environment using the ENVIRON associative array. e.g.

Code:

$ export VAR="J. R. Bob Dobbs"
$ echo "Hi" | awk '{ print $1 " " ENVIRON["VAR"] }'
Hi J. R. Bob Dobbs

sharathkv25 · 02-16-2007, 02:29 AM

Quote:

Originally Posted by matthewg42

In awk, you can access variable which have been exported to the environment using the ENVIRON associative array. e.g.

Code:

$ export VAR="J. R. Bob Dobbs"
$ echo "Hi" | awk '{ print $1 " " ENVIRON["VAR"] }'
Hi J. R. Bob Dobbs

Hi,

I am able to access the shell variable in awk, as you can see in my my script posted above.

I need to know how to set a value to a shell variable from AWK, so I can use the variable in shell later on?

Thanks

matthewg42 · 02-16-2007, 03:05 AM

Quote:

Originally Posted by sharathkv25

Hi,

I am able to access the shell variable in awk, as you can see in my my script posted above.

Not really. When you do this:

Code:

$ VAR=test
$ awk '{ print '$VAR' }'

...you are executing the command:

Code:

awk '{ print test }'

Awk never sees the string "$VAR" - the shell pre-expands this before invoking awk - you have basically excluded it from the single quotes and allowed the shell to interpolate $VAR. That it is working is an illusion, which will break in many cases - e.g. your variable has a space or tab in it. For example:

Code:

$ VAR="my test"
$ awk '{ print '$VAR' }'
awk: cmd. line:1: { print my
awk: cmd. line:1:           ^ unexpected newline or end of string

Quote:

I need to know how to set a value to a shell variable from AWK, so I can use the variable in shell later on?

Thanks

You can't set something in the environment of a parent process. The environment variables are inherited by a child process from it's parent. If you write to the environment variables in a process, it will modify the copy in the memory space of that process, but cannot send it to the parent.

You can however take the standard output of a program, and assign that to a variable in the shell. This is a very different mechanism, but depending on what you want to do, it can have a similar effect:

Code:

$ var=$(echo "J. R. Bob Dobbs" |awk '{ print $3 }')

This will execute the command:

Code:

$ echo "J. R. Bob Dobbs" |awk '{ print $3 }'

...and assign the output of that command to the variable var. In this case, var will be "Bob".

A more general description is that $(command) is interpolated as the output of "command".