Timeline for How can I declare and use Boolean variables in a shell script?
Current License: CC BY-SA 4.0
19 events
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| Aug 22, 2018 at 13:06 | history | edited | Peter Mortensen | CC BY-SA 4.0 |
Added a cross reference. Active reading [<http://en.wikipedia.org/wiki/Bash_%28Unix_shell%29>]. Changed to ISO 8601 date.
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| Jul 24, 2017 at 19:58 | comment | added | Mike Holt |
To address SeldomNeedy's comment, yes, you can use the real true, but generally not as something to compare a variable against, since the real true has no value per se. All it does is set the exit status to 0, indicating success. It's worth noting that it's essentially equivalent to the so-called "null command", or :. As far as using 0 and 1, that's what I do in all my scripts these days where I need booleans. And I use the (( )) operator instead of [[ ]] to evaluate. So, for example, if I have flag=0, I can then do if (( flag )); then ...
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| Jul 24, 2017 at 19:31 | comment | added | phil294 |
wouldnt it make more sense to use 0 and 1 instead of false and true then? aka if [[ $a == 0 ]]; then ..
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| Jul 23, 2015 at 23:59 | comment | added | Seldom 'Where's Monica' Needy |
From reading the answers offered here, I get the impression that there's no such thing as actually using the real true. Is there a way? I suspect many programmers who are used to stricter languages viewing this answer to assist them in mixing up some bash glue to make their lives a bit easier would want an === operator so that strings and "booleans" aren't actually interchangeable. Should they just stick to 0 and 1 and use (( $maybeIAmTrue )) as suggested in Quolonel Question's answer?
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| Jun 8, 2015 at 23:49 | comment | added | Mike Holt | @wisbucky Thanks for that. I hadn't realized that there was a prior version of miku's answer, although I did note in my update on 2/19/2014 that the article linked to in miku's answer was doing something different. | |
| Jun 8, 2015 at 23:10 | comment | added | wisbucky |
The reason for the confusion is that miku's original answer stood for 4 years. All the references to the builtin true were made regarding the original answer. (The revised answer on Feb 12, 2014 was not submitted by miku.) I have edited the answer to include both original and revised. Then people's comments make sense.
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| Apr 30, 2014 at 16:53 | history | edited | Mike Holt | CC BY-SA 3.0 |
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| Apr 30, 2014 at 14:56 | comment | added | Mike Holt |
@chepner You're right. I hate == and never use it in my own scripts. Not sure why I had that in there. Maybe just too much C on the brain.
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| Apr 30, 2014 at 12:32 | comment | added | chepner |
Using == with [/test is not portable; if you want to use ==, use [[. If you want to use [, use =.
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| Apr 14, 2014 at 17:09 | history | edited | Mike Holt | CC BY-SA 3.0 |
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| Apr 14, 2014 at 17:01 | history | edited | Mike Holt | CC BY-SA 3.0 |
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| Feb 20, 2014 at 1:19 | comment | added | Mike Holt | True. Although, I'm not advocating for (or against) either approach. I just wanted to clear up some of the misinformation that's getting voted up here, so that people who stumble upon this topic later on won't walk away with a bunch of misconceptions about how this all works. | |
| Feb 20, 2014 at 1:14 | history | edited | Mike Holt | CC BY-SA 3.0 |
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| Feb 20, 2014 at 1:11 | comment | added | ajk |
The no-bracket approach also has the advantage of letting you write clean, clear (imo) one-liners like $the_world_is_flat && echo "you are in flatland!"
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| Feb 20, 2014 at 1:09 | history | edited | Mike Holt | CC BY-SA 3.0 |
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| Feb 20, 2014 at 1:03 | history | edited | Mike Holt | CC BY-SA 3.0 |
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| S Feb 14, 2014 at 0:00 | review | Late answers | |||
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| S Feb 14, 2014 at 0:00 | review | First posts | |||
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| Feb 13, 2014 at 23:45 | history | answered | Mike Holt | CC BY-SA 3.0 |