Is there any significant difference between using [[ $a -lt 2 ]] and (( $a < 2 ))?
For example, is one of them faster or more POSIX compliant than the other?
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Alexej Magura
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Related (but not duplicate) [Is test or [ or [[ more portable both between bash shells and between other shells](http://unix.stackexchange.com/questions/168255/) – roaima Oct 04 '16 at 21:10
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1`(( $a < 2 ))` is a valid *command* in `bash`, distinct from the *expression* `$(( $a < 2 ))`. – chepner Oct 04 '16 at 21:12
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1also related: http://unix.stackexchange.com/q/306111/170373 – ilkkachu Oct 04 '16 at 21:13
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@chepner one learns something new each day. thank you – roaima Oct 04 '16 at 21:38
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Neither is POSIX-compatible. In a POSIX shell, you can use the command [ "$a" -lt 2 ] or the expression $(( a < 2 )).
In bash, the former is simply the conditional command supporting a superset of the conditional expressions that [ supports, and the latter is a standalone command that exits with status 0 if the enclosed arithmetic expression is non-zero, or 1 otherwise. Other than readability, there is no significant difference between the two when used properly.
Jeff Schaller
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chepner
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1`(( ))` and `$(( ))` would perhaps make it easier to mix other arithmetic in, if that's ever needed? – ilkkachu Oct 04 '16 at 21:22
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Is `[` available in any shell? If there would be a shell where `[` is not built-in then ``$(( ))`` could be significant faster. – rudimeier Oct 04 '16 at 22:30
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1@rudimeier In theory `[` can be external but in practice it's always built in. – Gilles 'SO- stop being evil' Oct 05 '16 at 00:12