Assigning system command's output to variable

Question

I want to run the system command in an awk script and get its output stored in a variable. I've been trying to do this, but the command's output always goes to the shell and I'm not able to capture it. Any ideas on how this can be done?

Example:

$ date | awk --field-separator=! {$1 = system("strip $1"); /*more processing*/} 

Should call the strip system command and instead of sending the output to the shell, should assign the output back to $1 for more processing. Rignt now, it's sending output to shell and assigning the command's retcode to $1.

Answer 1

Note: Coprocess is GNU awk specific. Anyway another alternative is using getline

cmd = "strip "$1 while ( ( cmd | getline result ) > 0 ) {   print  result }  close(cmd) 

Calling close(cmd) will prevent awk to throw this error after a number of calls :

fatal: cannot open pipe `…' (Too many open files)

Answer 2

To run a system command in awk you can either use system() or cmd | getline.

I prefer cmd | getline because it allows you to catch the value into a variable:

$ awk 'BEGIN {"date" |  getline mydate; close("date"); print "returns", mydate}' returns Thu Jul 28 10:16:55 CEST 2016 

More generally, you can set the command into a variable:

awk 'BEGIN {        cmd = "date -j -f %s"        cmd | getline mydate        close(cmd)      }' 

Note it is important to use close() to prevent getting a "makes too many open files" error if you have multiple results (thanks mateuscb for pointing this out in comments).

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Using system(), the command output is printed automatically and the value you can catch is its return code:

$ awk 'BEGIN {d=system("date"); print "returns", d}' Thu Jul 28 10:16:12 CEST 2016 returns 0 $ awk 'BEGIN {d=system("ls -l asdfasdfasd"); print "returns", d}' ls: cannot access asdfasdfasd: No such file or directory returns 2