running a for loop using command as end index valrible

Question

I would like to run a for loop in bash where end index is result of a command

#!/bin/bash
# Basic range in for loop
for value in {0..$(ls | wc -l)}   
do
echo $value
done

But when I run it I see:

{0..14}

Brace expansion happens before variable does in bash. that wont work. That question has been asked and answered many-many times in this forum. Use a cstyle for-loop. — Jetchisel
– Jetchisel, Commented May 18, 2020 at 12:26
Further, ls | wc -l is not a robust way to get (presumably) the number of files in a directory. — chepner
– chepner, Commented May 18, 2020 at 12:48

Mahmoud Odeh · Accepted Answer · 2020-05-18 13:40:33Z

1

you can use eval :

for value in $(eval echo {0..$(ls | wc -l)})   
do
echo $value
done

seq is similar to bash's braces, The key advantage of seq is that its arguments can include not just arithmetic expressions, as shown above, but also shell variables

for value in $(seq 1 `ls | wc -l`);
do
    echo ${value}
done

By contrast, the brace notation will accept neither.

seq is a GNU utility and is available on all linux systems as well as recent versions of OSX. Older BSD systems can use a similar utility called jot.

C-Style- pretty and simple :

for ((value = 1 ; value <= $(ls | wc -l) ; value++)); do
  echo ${value}
done

edited May 18, 2020 at 13:40

answered May 18, 2020 at 13:22

Mahmoud Odeh

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