Bash - arithmetic in array index

Question

Say I have an array arr and an index x. How do I assign something to the array at index x+1? I'm getting bugs by trying the following, if one of them is correct I'd love to know which one and if not what am I doing wrong?

arr[$x+1]="hi"      # Doesn't work
arr[$((x+1))]="hi"  # Nope

References: The [Bash guide for beginners](http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_10_02.html) says an array index "is treated as an arithmetic expression that must evaluate to a positive number." [Arithmetic expressions](http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_03_04.html#sect_03_04_05) are whatever can go inside `$(( ))`. — cxw, May 19 '18 at 12:53

score 3 · Accepted Answer · answered Dec 24 '13 at 14:49

3

Almost there.

arr[(($x+1))]="hi"

answered Dec 24 '13 at 14:49

Ignacio Vazquez-Abrams

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1

So why would I be getting this: ./win.bash: line 114: syntax error near unexpected token `(' ./win.bash: line 114: ` let game[(($j+1))]=$tmp' – Dori Dec 24 '13 at 14:58
You're not using bash as your interpreter. Or you're using an old version. – Ignacio Vazquez-Abrams Dec 24 '13 at 14:59
bash --version: v 4.1.2(1) – Dori Dec 24 '13 at 15:00
`x` is neither a number nor a variable. – Ignacio Vazquez-Abrams Dec 24 '13 at 15:03
1

`x` isn't a variable? It's my loop index... `for (( x=0; x – Dori Dec 24 '13 at 15:08
Regarding whether or not `x` needs dereferenced, see https://stackoverflow.com/q/40104348/915044 – TomRoche Jun 24 '19 at 00:41

Bash - arithmetic in array index

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