topic Re: Capturing awk "system" command to awk variable? in Operating System - Linux

Capturing awk "system" command to awk variable?

Simon Hargrave — Thu, 26 Aug 2004 08:07:23 GMT

Within awk, there is the system() function that lets me run a system command. However this only lets me capture the return code.

How can I capture the output into an awk variable? I know this can be done in perl etc, but I'm using awk, so...

eg (in a simple case): -

awk '{fred=`system("df $1")` ; split(fred,bill) ; print $1" uses "bill[4]" blocks."}' filesystems

I know THIS example can be done in other ways, but it's taken as part of a larger context in awk which is why I need awk.

Any ideas?

Re: Capturing awk "system" command to awk variable?

Rodney Hills — Thu, 26 Aug 2004 08:39:48 GMT

You can use the "getline" function-

"whoami" | getline

Will execute "whoami" and put the result into $0 (and also parse for fields).

"whoami" | getline myvar

Will instead put the result into myvar.

HTH

-- Rod Hills

Re: Capturing awk "system" command to awk variable?

Simon Hargrave — Thu, 26 Aug 2004 08:55:35 GMT

Spot on, cheers!

Re: Capturing awk "system" command to awk variable?

Hein van den Heuvel — Thu, 26 Aug 2004 09:00:33 GMT

man awk....

"Finally, cmd | getline pipes the output of cmd into getline; each call of getline returns the next line of output from cmd."

Example:

awk 'BEGIN{while ("ps" | getline){ print "test " $1 " test"}}' /dev/null | more

This is similar to the following hack:

mknod x
awk 'BEGIN{system("ps >> x&"); while (getline < "x"){ print "test " $1 " test"}}' /dev/null
rm x

The are (gawk) extensions (Tru64) that have more support in this area. Like a native "&",
and close(file[, how]) to close files, pipes, or (two-way) pipse to co-processes.

Enjoy,
Hein.

Re: Capturing awk "system" command to awk variable?

Ceesjan van Hattum — Thu, 26 Aug 2004 09:26:18 GMT

The solutions above soes not give you
answers to the question how to get
systemoutput into a variable(!).
So here is the answer:
DO NOT USE system(), but escape back
to the shell:

awk '{ ...
x="'"`date`"'"
printf "%s\n",x
}'

Regards,
Ceesjan

Re: Capturing awk "system" command to awk variable?

Kuntal Roy — Tue, 26 Dec 2006 21:39:08 GMT

Hi Ceesjan,

How a dynamic string can be pushed in the command e.g. du -s ...

Thanks,
Kuntal

Re: Capturing awk "system" command to awk variable?

James R. Ferguson — Tue, 26 Dec 2006 22:21:45 GMT

Hi Kuntal:

Welcome to the Forums! You should really not resurrect old threads, but rather post your own queries. That said, however, you asked:

> How a dynamic string can be pushed in the command e.g. du -s ...

# awk -v DIR="/tmp" 'END{while ("du -s " DIR|getline) {print}}' /dev/null

Note that there is a space (blank) character after the '-s' flag and before the variable passed from the shell to 'awk' --- DIR.

Regards!

...JRF...

Re: Capturing awk "system" command to awk variable?

Kuntal Roy — Wed, 27 Dec 2006 11:00:31 GMT

Thanks for the respose. I think, my question was not clear enough.

I have scenario such that instead of putting some static command 'date', I need to pass some dynamic string as a command - du -s | awk '{print $1}'. I am already inside an awk command.

awk '{ ...
x="'"`date`"'"
printf "%s\n",x
}'

Re: Capturing awk "system" command to awk variable?

Dennis Handly — Thu, 04 Jan 2007 01:49:37 GMT

>Kuntal: I have scenario such that instead of putting some static command 'date',

Can you evaluate the command before you invoke awk? If not, you could invoke awk, execute the command and then go back in awk.