Question

I need to execute a command per line of some file. For example:

file1.txt 100 4
file2.txt 19 8

So my awk script need to execute something like

command $1 $2 $3

and save the output of command $1 $2 $3, so system() will not work and neither will getline. (I can t pipe the output if I do something like this.)

The restriction to this problem is to use only awk. (i already had a solution with bashscriot + awk...but I only want awk...just to know more about this)

Answer 1

What s wrong with using getline?

$ ./test.awk test.txt
# ls -F | grep test
test.awk*
test.txt

# cat test.txt | nl
     1  ls -F | grep test
     2  cat test.txt | nl
     3  cat test.awk

# cat test.awk
#!/usr/bin/awk -f
{
        cmd[NR] = $0
        while ($0 | getline line) output[NR] = output[NR] line RS
}
END {
        for (i in cmd) print "# " cmd[i] ORS output[i]
}

Answer 2

Awk s system() function passes the string to /bin/sh, so you can use redirect operators, like ">file.out" if you want.

awk  {system("command " $1 " " $2 " " $3 ">" $1 ".out");}

Edit: ok, by save, you mean into an awk variable. ephemient is on the right track, then. That s what awk s getline does, like backticks or $(cmd) in shell/perl. In fact, google for awk backticks found this: http://www.omnigroup.com/mailman/archive/macosx-admin/2006-May/054665.html

You say you can t use getline because then you couldn t pipe. But you can work around that with tee and file-descriptor tricks. This works if /bin/sh is bash:

{ "set +o posix; command " $1 " " $2 " "  $3  " | tee >(grep foo)"  | getline var; print toupper(var); } # bash-only, and broken.

set +o posix is necessary because awk runs bash as sh, which makes it go into posix mode after readings its startup files. Hmm, I m not having any luck getting that to work, and it requires bash anyway.

Ok, this works:


    $ touch foo bar
    $ echo "foo bar" | 
      awk  { "{ ls " $1 " " $2 " "  $3  " | tee /dev/fd/10 | grep foo > /dev/tty; } 10>&1"  | getline var; print toupper(var); } 
    foo
    BAR

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