BAD SUBSTITUTION: String comparison using array elements in bash

Question

I'm getting started with bash programming, and am stumbling through the syntax a little. The following is part of the code to play tic-tac-toe from the command line.

i=0
initialGrid=('_' '_' '_' '_' '_' '_' '_' '_' '_')
if [ "${ initialGrid[ $i ] }" = "_" ]; then
echo "I'm here"
fi

However I get the following error

tic.sh: line 48: ${ initialGrid[ $i ] }: bad substituion

So the echo never gets executed

I was able to substitute the above if statement and do the following without error

element=" $initialGrid[$i] "
if [ "${!element}" = "_" ]; then
echo "Element equals underscore"
fi

But again, the echo never gets execute even though i believe it clearly should

Jahid · Accepted Answer · 2015-06-10 10:31:01Z

2

Spaces are not optional. You need to use:

if [[ "${initialGrid[i]}" == "_" ]]; then echo "I'm here"; fi

edited Jun 10, 2015 at 10:31

Jahid

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answered Jun 9, 2015 at 20:52

anubhava

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Comments

Pawel Veselov · Accepted Answer · 2015-06-09 20:55:47Z

0

Spaces in bash almost always are special characters. In your first case:

i=0
initialGrid=('_' '_' '_' '_' '_' '_' '_' '_' '_')
if [ "${ initialGrid[ $i ] }" = "_" ]; then
  echo "I'm here"
fi

You need to replace the line with the condition with

if [ "${initialGrid[$i]}" = "_" ]; then

In your second case, you are padding the value with spaces, but then trying to compare it to the value without spaces, _ is not the same as _. You are also not dereferencing the array correctly.

element=" $initialGrid[$i] "
if [ "${!element}" = "_" ]; then
  echo "Element equals underscore"
fi

Replace the first line with element="${initialGrid[$i]}"

answered Jun 9, 2015 at 20:55

Pawel Veselov

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