[SOLVED] nested for loop

Drosera_capensis · 03-05-2020, 07:43 AM

Hello everyone,

I have a little issue with a nested for loop, and I don't understand what is not working in.

I try to output the following files:

title_one_1.txt
title_one_2.txt
title_one_3.txt
title_two_1.txt
title_two_2.txt
title_two_3.txt
title_three_1.txt
title_three_2.txt
title_three_3.txt

Therefore, I set up a nested for loop to output this list.

array="one two three"
for f in $array
do
for p in {1..3} ;
do
echo title_$f_$p.txt
done ;
done

But it is not working. It seems that variables as $f are not processed with underscores, but with dots.
Would anyone know how to output the list above?

Turbocapitalist · 03-05-2020, 07:52 AM

Which shell interpreter have you chosen? If it's the POSIX shell, then you'll need another way of doing the count from 1 to 3. Here is one of several:

Code:

#!/bin/sh

array="one two three"
for f in $array
do
        for p in $(seq 1 3)
        do
                echo title_${f}_${p}.txt
        done
done

exit 0

Also, the shell variables allow underscores in the name so you will need curly braces to limit the name to just the letters you mean. In otherwords, you want ${f} and ${p} rather than ${f_p} as you currently had it.

TenTenths · 03-05-2020, 08:04 AM

If you are using bash and trying to do anything like this always enclose your variable name with {} so that bash knows what variable you are talking about.

If you use ${f} instead of $f you'll find it should work as you expect.

Without {} bash is actually looking for a variable $f_ in your example rather than just $f

So:

Code:

array="one two three"
for f in $array ; do
  for p in {1..3} ; do
    echo title_${f}_${p}.txt
  done
done

Drosera_capensis · 03-05-2020, 09:00 AM

Thank you Turbocapitalist, I am working on BASH shell, but I keep preciously your answer.

Thanks a lot for your command and for the nice explanations TenTenths! I will make some experiments with $f and ${f} in my commands.