Determine if Array Has Elements in IF/Then Statement In Bash

Question

I'm trying to determine if an array has elements in an if/then statement like this:

if [[ -n "$aws_user_group" && -n "${#aws_user_roles[@]}" ]]; then
  echo "$aws_user_name,$aws_user_group,"${aws_user_roles[*]}",$aws_key,$aws_account_number" >> "$ofile"
 elif [[ -n "$aws_user_group" ]]; then
  echo "$aws_user_name,$aws_user_group,,$aws_key,$aws_account_number" >> "$ofile"
fi

Problem is, if the array is empty it's represented by '0' as in this debug output:

   [[ -n 0 ]]

And the wrong line prints out. It prints the line that includes the 'role' output but leaves it blank.

How can I check a string variable and a mathematical variable in the same if/then statement?

-n and -z are non-zero and zero length strings, not for mathematical comparisons. — jeremysprofile
– jeremysprofile, Commented Oct 30, 2018 at 18:48

Paul Hodges · Accepted Answer · 2018-10-30 18:56:37Z

2

Zero is the number of elements. Use a mathematical evaluation.

if (( ${#aws_user_roles[@]} )) # HAS ELEMENTS
then echo has elements
else echo is empty
fi

example

$: declare -i foo=()
$: if (( ${#foo[@]})); then echo elements; else echo empty; fi
empty
$: foo=( 1 2 3 )
$: if (( ${#foo[@]})); then echo elements; else echo empty; fi
elements

as an aside...

$: foo=( 1 2 3 )
$: if (( ${#foo})); then echo elements; else echo empty; fi
elements

also works, but ${#foo} is really only looking at the string length of first element, and could theoretically give you a false response...though '' returns 1. Hmm...

You can also chain tests for other things -

if (( ${#var} )) && [[ -e "$var" ]] # both must succeed

This is the same as one-liner tests

ls a && ls b || echo one of these doesn't exist...

edited Oct 30, 2018 at 18:56

answered Oct 30, 2018 at 18:42

Paul Hodges

16k1 gold badge24 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

bluethundr Over a year ago

Ok, thanks. Any way to combine the mathematical test with the test to see if the other variable with text has a value: -n "$aws_user_group" ?

Paul Hodges Over a year ago

just use && between your tests. See above.

bluethundr Over a year ago

Ok thanks. Also I tried this and it works: if [[ -n "$aws_user_group" && -n "${aws_user_roles[@]}" ]]; then

Collectives™ on Stack Overflow

Determine if Array Has Elements in IF/Then Statement In Bash

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related