bash do loop with length of directory

Question

I am trying to loop through filenames within a directory so I can perform an operation on each.

I am able to loop through just 10 filenames if I use:

var=($(ls directory))
for k in {1..10}
do
    echo ${var[$k]}
done

Which gives me the first 10 filenames in my directory. However, I want to loop through them all.

If I do:

length=($(ls directory -1 | wc -l))

I get the length (for this example, it is 62)

So when I combine everything together:

var=($(ls directory))
length=($(ls directory -1 | wc -l))
for k in {1..$length} 
do
    echo ${var[$k]}
done

I get the error 'syntax error: operand expected (error token is "{1..62}")

Any help to fix this, or a better solution would be greatly appreciated!

Brace expansion is both powerful and limited. Observe that it happens before any variables are expanded, so any attempt to use {1..$length} is doomed to failure. — Jonathan Leffler
– Jonathan Leffler, Commented Apr 22, 2016 at 17:33

heemayl · Accepted Answer · 2016-04-22 17:38:43Z

2

Brace expansion is performed by shell before variable expansion, hence you are getting the error.

You can use:

for k in $(seq 1 "$length")

to get around the problem.

Also what you are doing can be easily done by:

files=( * )
for i in "${files[@]}"; do echo "$i"; done

or even simpler:

printf '%s\n' "${files[@]}"

edited Apr 22, 2016 at 17:38

answered Apr 22, 2016 at 17:21

heemayl

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1 Comment

WX_M Over a year ago

Perfect! Thank you for your help!

SLePort · Accepted Answer · 2016-04-22 17:50:33Z

1

Why not simply :

for file in *; do
  if [ -f "$file" ]; then
    echo "Do what you want with" "$file"; 
  fi
done

edited Apr 22, 2016 at 17:50

answered Apr 22, 2016 at 17:38

SLePort

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4 Comments

Jonathan Leffler Over a year ago

The one problem that neither your answer nor the other answer (as I type) deals with is that ls directory part. Up to a point, using directory/* would work; it would give the names in a usable format (and shopt -s nullglob might be beneficial). However, the ls command would give just file where directory/* would yield directory/file. That can be dealt with (by basename, for example, or with minor caveats ${file##*/}) in the loop.

SLePort Over a year ago

Added a test to get files.

rici Over a year ago

@JonathanLeffler: Or: (cd directory; for file in *; do ...; done)

Jonathan Leffler Over a year ago

@rici: that's probably OK, unless the processing relies on being in the current directory at the start of each processing step, rather than in a distant directory. Problems could relate to commands or files not found that would be found if the cd had not been done Probably OK, but not guaranteed.

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