Instead of let expr, prefer (( expr )) .

Problematic code:

let a++

Correct code:

(( a++ ))

Rationale:

The (( .. )) arithmetic compound command evaluates expressions in the same way as let, except it's not subject to glob expansion and therefore requires no additional quoting or escaping.

This warning only triggers in Bash/Ksh scripts. In Sh/Dash, neither let nor (( .. )) are defined, but can be simulated with [ $(( expr )) -ne 0 ] to retain exit code, or : $(( expr )) to ignore it.

Exceptions:

None.

More information

• Bash Hacker's Wiki: The let builtin command