[SOLVED] Opposite to expected response in awk

rng · 12-08-2015, 10:06 PM

I am using following awk code on a file called dirlist. However, it is giving reverse response- printing out directories if they are there when asked about not there and vice versa:

Code:

$ cat dirlist
/root
/boot
/sys
/a_dir
/b_dir

# TRYING TO PRINT IF DIRECTORY IS PRESENT: 
$ cat dirlist | awk ' { if ( system(" [ -d " $1 " ] ")  ) print $1 } '
/a_dir
/b_dir

# TRYING TO PRINT IF DIRECTORY IS ABSENT: 
$ cat dirlist | awk ' { if ( system(" [ ! -d " $1 " ] ")  ) print $1 } '
/root
/boot
/sys

Where is the problem. Thanks for your insight.

berndbausch · 12-08-2015, 11:33 PM

system() returns the command's exit status. "[ -d a_dir ]" has an exit status of 0 when a_dir exists, and 1 when it doesn't exist.

Now when the if condition is nonzero, awk considers it as true. So, a nonexisting directory returns 1, which is true.

rng · 12-09-2015, 01:45 AM

Perfect explanation.