Bash assignment with "let" fails with "/"

Question

I'm using GNU bash, versión 5.0.3(1)-release (x86_64-pc-linux-gnu), and I wonder why a simple assignment statement gives a syntax error:

#/bin/bash

var1=/tmp       # This works
let var2=/tmp   # This fails with syntax error: Operand expected (error is "/tmp")

Does anybody know why? Thanks

help let should show you why...

Jetchisel
– Jetchisel

2020-05-05 10:05:10 +00:00
Commented May 5, 2020 at 10:05 — Jetchisel
– Jetchisel, Commented May 5, 2020 at 10:05

Bayou · Accepted Answer · 2020-05-05 10:04:12Z

2

let is used only for arithmetic operations, just as (( )).

Therefore, the following lines are the same

a=$((60 * 60))
let a=(60*60)
((a = 60 * 60))

See the manpage.

answered May 5, 2020 at 10:04

Bayou

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Comments

Inian · Accepted Answer · 2020-05-05 10:16:12Z

1

let is a shell builtin that is a another way to use the $((..)) Arithmetic Expansion in bash. The assignment

let var2=/tmp

is treated by the shell as an arithmetic operation "division" with an incorrect quotient value. It is equivalent to doing.

var=$((/tmp))

Since there are incorrect number of operands, the parser has thrown the error that you are seeing. Note that tmp is still treated in a variable context by the shell. If the parser had identified the expression as valid, then tmp would have undergone variable expansion. Since it is not set before, it would have likely thrown a "division-by-zero" error.

For simple variable assignments just drop the let keyword and enclose the value field within "quotes"

var2="/tmp"

edited May 5, 2020 at 10:16

answered May 5, 2020 at 10:08

Inian

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