Bash array variable expansion inside expect command

Question

An extension to this question : Bash : Adding extra single quotes to strings with spaces

After storing the arguments of command as a bash array

touch "some file.txt"
file="some file.txt"
# Create an array with two elements; the second element contains whitespace
args=( -name "$file" )
# Expand the array to two separate words; the second word contains whitespace.
find . "${args[@]}"

Then storing whole command in an array

finder=( find . "${args[@]}" )

In bash I am able to run the command as below:

"${finder[@]}"
./some file.txt

But when I tried using expect, I am getting error

expect -c "spawn \"${finder[@]}\""
missing "
   while executing
"spawn ""
couldn't read file ".": illegal operation on a directory

Why is bash variable expansion not happening here?

John Kugelman · Accepted Answer · 2016-03-08 14:19:03Z

5

expect -c COMMAND requires COMMAND to be a single argument. It doesn't accept multi-word arguments, which is what "${finder[@]}" expands to.

If you want to handle whitespace perfectly without mangling it'll be tricky. printf %q might be of use.

answered Mar 8, 2016 at 14:19

John Kugelman

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muru · Accepted Answer · 2016-03-08 14:38:22Z

0

${finder[@]} in double quotes expands into separate words:

$ printf "%s\n" expect -c "spawn \"${finder[@]}\""
expect
-c
spawn "a
b
c"

So, expect is not getting the entire command as a single argument. You could use *:

$ printf "%s\n" expect -c "spawn \"${finder[*]}\""
expect
-c
spawn "a b c"

${finder[*]} expands the array elements into a single word separated by the first character of IFS, which is space by default. However, there is no distinction between spaces added by * and the whitespace in the original elements, so, you cannot reliably use this.

edited Mar 8, 2016 at 14:38

answered Mar 8, 2016 at 14:17

muru

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4 Comments

chepner Over a year ago

Try this with the user's original arguments; you'll get spawn "find . -name some file.txt".

muru Over a year ago

@chepner added note about that.

chepner Over a year ago

Providing an answer for a question about bash arrays that only works if the elements of the arrays don't contain whitespace is not useful. The entire reason for arrays to exist is to handle elements that contain whitespace.

chepner Over a year ago

The actual error actually seems to be the very first quoted ", so I don't think you've addressed the problem at all.

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