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 says an array index "is treated as an arithmetic expression that must evaluate to a positive number." Arithmetic expressions are whatever can go inside $(( )). — cxw
– cxw, Commented May 19, 2018 at 12:53

Ignacio Vazquez-Abrams · Accepted Answer · 2013-12-24 14:49:43Z

4

Almost there.

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

answered Dec 24, 2013 at 14:49

Ignacio Vazquez-Abrams

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6 Comments

Dori Over a year ago

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'

Ignacio Vazquez-Abrams Over a year ago

You're not using bash as your interpreter. Or you're using an old version.

Dori Over a year ago

bash --version: v 4.1.2(1)

Ignacio Vazquez-Abrams Over a year ago

x is neither a number nor a variable.

Dori Over a year ago

x isn't a variable? It's my loop index... for (( x=0; x<total; x+=2 )) And about the version problem, nevermind... I found out x is empty when the bug is reached

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