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 t

Answer 1

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