Why should arithmetic operators be padded by space in expr?

Question

Using expr to evaluate an expression in bash, the following happened

bash-3.2$ expr 1+1
1+1
bash-3.2$ expr 1 + 1
2

Why should the plus sign be padded by space for it to be interpreted as mathematical operation?

From the documentation `Each token of the expression must be a separate argument.` — user3483203, Jan 14 '18 at 22:12

score 4 · Accepted Answer · answered Jan 14 '18 at 22:11

4

I suspect this has little to do with bash. From the man page of expr :

All operators and operands must be passed as separate arguments

In order for operands and operators to be interpreted as separate arguments, You have to separate them (with a space).

answered Jan 14 '18 at 22:11

francesco foresti

1 Answers1