I experimented on the latest mac OS with a shell scrip "a.sh" with the following content (exact copy).
#!/bin/bash
echo $BASH_VERSION
a=0
(( a < 100 || 1 / a < 2 )) && echo ok
I got:
3.2.57(1)-release
./a.sh: line 4: ((: a < 100 || 1 / a < 2 : division by 0 (error token is "< 2 ")
Since a < 100 is already true, I thought 1 / a < 2 wouldn't be evaluated.
Can someone help me understand this?
There are two circumstances you got this error:
Bash 3.2.57 evaluates both sides of a logical or within an arithmetic expression.
or because you used a single | bit-wise ∨, rather than a double || logical ∨ boolean expression operator:
LC_ALL=C bash -c 'a=0; (( a < 100 | 1 / a < 2 )) && echo ok'
bash: ((: a < 100 | 1 / a < 2 : division by 0 (error token is "a < 2 ")
LC_ALL=C bash -c 'a=0; (( a < 100 || 1 / a < 2 )) && echo ok'
ok
Reason:
| is the bit-wise or operator.
When used as:
a < 100 | 1 / a < 2,
the bit-wise or applies as:
100 | 1,
witch in binary is equivalent to 01100100 ∨ 00000001 → 01100101 binary or 101 base-10.
Finally:
a < 100 | 1 / a < 2 turns-out to be:
a < 101 / a < 2.
When a=0:
0 < 101 / 0 < 2