Bash script, array not getting created as expected

Question

I'm pretty new to bash scripting and I'm obviously missing some fairly basic understanding as I can't work out why this script isn't doing as I'd expect. I've made a simple example reproducing the problem, it is supposed to make 3 folders, with 3 folders inside, then touch a file test inside of each.

Here's the script:

#!/bin/sh
DIR_LEVEL_1=("1" "2" "3")
for DIR_1 in ${DIR_LEVEL_1[@]}; do
  mkdir $DIR_1
  DIR_LEVEL_2=("$DIR_1/a" "$DIR_1/b" "$DIR_1/c")
  echo $DIR_LEVEL_2
  for DIR_2 in ${DIR_LEVEL2[@]}; do
    mkdir $DIR_2
    touch "$DIR_2/test"
  done
done

The problem I was having was the it wasn't entering the second for loop, I put in that echo and it looks like the second array isn't being created properly as the output of the script is:

1/a
2/a
3/a

which is just the first element of the array.

running with -xv flag I get this, which shows it's taking no notice of that nested for loop (I guess because the array didn't get created as I wanted?)

#!/bin/sh
DIR_LEVEL_1=("1" "2" "3")
+ DIR_LEVEL_1=("1" "2" "3")
for DIR_1 in ${DIR_LEVEL_1[@]}; do
  mkdir $DIR_1
  DIR_LEVEL_2=("$DIR_1/a" "$DIR_1/b" "$DIR_1/c")
  echo $DIR_LEVEL_2
  for DIR_2 in ${DIR_LEVEL2[@]}; do
    mkdir $DIR_2
    touch "$DIR_2/test"
  done
done
+ for DIR_1 in '${DIR_LEVEL_1[@]}'
+ mkdir 1
+ DIR_LEVEL_2=("$DIR_1/a" "$DIR_1/b" "$DIR_1/c")
+ echo 1/a
1/a
+ for DIR_1 in '${DIR_LEVEL_1[@]}'
+ mkdir 2
+ DIR_LEVEL_2=("$DIR_1/a" "$DIR_1/b" "$DIR_1/c")
+ echo 2/a
2/a
+ for DIR_1 in '${DIR_LEVEL_1[@]}'
+ mkdir 3
+ DIR_LEVEL_2=("$DIR_1/a" "$DIR_1/b" "$DIR_1/c")
+ echo 3/a
3/a

So it only creates the first level of folders

camh · Accepted Answer · 2012-04-17 12:09:54Z

4

You have three problems here:

The script should start with #!/bin/bash if you want to use bash, not #!/bin/sh
echo $ARRAY will output only the first element of the array, not the whole array, which is why it looks like it is doing only the first element - it is not, but it is just printing the first. Use echo ${ARRAY[@]} to output the whole array.
When you are iterating the second array, you have the variable name wrong. Your array is DIR_LEVEL_2, but you are iterating ${DIR_LEVEL2[@]}, which is empty (hence no iteration). You are missing an underscore before the 2

answered Apr 17, 2012 at 12:09

camh

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2 Comments

GP89 Over a year ago

Ah thanks! I was confused as I'd expect some sort of error typically for undefined variables. I also got a bit stuck with another mistake I made in my main script which didn't make it to the sample which was putting a space after the = when declaring a variable, I didn't realise you couldn't do that!

Mark Reed Over a year ago

Shell syntax is unusually picky about spaces, etc, because it has to coexist with executing commands. Thus, foo = bar runs the command foo with two arguments, = and bar, while foo=bar is an assignment. If you want an error when you access an undefined variable, add set -u to the top of your script.

kojiro · Accepted Answer · 2012-04-17 12:07:19Z

3

Well, the real issue with your script is that you create DIR_LEVEL_2, but you iterate over DIR_LEVEL2. (Note the underscore difference). However, you also neglect to quote "${array[@]}", which means it will not wordsplit properly. All that aside, might I suggest you use brace expansion to make this entire thing a better experience?

#!/bin/bash

dirs=( {1,2,3}/{a,b,c} )
mkdir -p "${dirs[@]}"
for d in "${dirs[@]}"; do
    touch "$d/test"
done

Edit/postscript: I notice your script above uses #!/bin/sh, but you've tagged this post bash. They are not the same thing. Unless you're certain you want to trade the greater featureset of bash for the greater portability of sh, use #!/bin/bash.

answered Apr 17, 2012 at 12:07

kojiro

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2 Comments

William Pursell Over a year ago

No need for the loop: mkdir -p {1,2,3}/{a,b,c}; touch {1,2,3}/{a,b,c}/test

kojiro Over a year ago

@WilliamPursell very true. I wanted to leave an example of looping properly (including quoting the array expansion) intact, but I should've mentioned that the loop is unnecessary for the actual task at hand.

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