The
*test*
and *[*

(square bracket) commands (44.20
)
can compare two numbers.
But it's an error if one of the numbers you test is stored in a shell variable
that's empty or doesn't exist.
For example, an empty *num*
variable here will give you a ```
Syntax
error
```

:

if [ "$num" -gt 0 ]
then ...

To stop syntax errors, add a leading zero, like this:

if [ "0$num" -gt 0 ]
then ...

In that case, if `$num`

is empty, the test will compare `0`

to
`0`

.
If `$num`

is `1`

, the test will be true (because `01`

is
greater than `0`

)-and so on, just as it should be.