[Discuss] through the looking glass

[jdm at moylan.us (dan moylan)]

richard pieri writes:
On 6/1/2018 7:32 PM, dan moylan wrote:
>> also b2 writes out empty files abc and xyz.
>>
>> i've surely missed something fundamental, or did i just
>> step into an alternate universe?

> What you missed isn't so obvious.

> "[" is a synonym for /bin/test with the caveat that a closing "]" is
> required. What's happening is that "[ $st1 > $st2 ]" becomes:

>   /bin/test abc > xyz

> "/bin/test abc" returns true, and you get an empty file because test
> generates no output, only return codes 0 (true) or 1 (false).

> The portable fix is to rewrite your logic because the test command only
> allows for "=" and "!=" in string comparisons.

> The bash-specific fix is to change your single brackets to double
> brackets: "[[ $st1 > $st2 ]]". "[[" is a bash built-in and it bypasses
> all of the above problems. But it's not portable.

thanks for your lucid explanation.

looking at o'reilly's "learning the bash shell" 2nd edition,
page 118, the < and > comparisons certainly seem to be
allowed.  nowhere in the book have i been able to find a
discussion of using [[ and ]] (though i have some vague
recollection of having run into that before).

escaping the comparison operators seems to work as well.
which might be preferred?

not portable?  where would that be?

thanks again,
ole dan

j. daniel moylan
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