Question

Question :

I’m breaking my teeths under this:

awk -v full=wc -v empty=wp '{
     ...blablabla...
     if ($4==full) stop=yes
     if (stop==yes && $4==empty) exit
     ...blablabla...
     }'

The code works well (I mean, I get an output) if I don’t declare the two variables full and empty at the beginning, and use instead the values of these in the script. If I only use the first variable in the script, I get the same output. But if I only use the second variable, I get no output at all.

Answer 1

Consider what happens when the variables are expanded. A portion of the awk body goes from:

' ... if ($4=='$full') ...'

to

' ... if ($4==wc) ...'

Since wc is a “bare word”, awk thinks it is a variable and substitutes it’s value (empty string), so you get this:

' ... if ($4=="") ...'

When you’re building your awk script, you need to be aware of quoting strings in awk. You need:

' ... if ($4=="'$full'") ...'

However, it is much more elegant to pass values with awk’s -v option as you have done.