Timeline for How can I declare and use Boolean variables in a shell script?
Current License: CC BY-SA 4.0
37 events
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| May 21 at 17:48 | history | edited | Benjamin Loison | CC BY-SA 4.0 |
Add a link to the mentioned comment
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| Dec 4, 2023 at 3:37 | comment | added | xuiqzy | Please add an explanation to your answer why this is your recommended solution compared to other options and how it behaves and works in bash. As far as I understand it's just a string comparison, so quoting the strings would be way clearer, when the word true implies there is some special syntax going on here that executes the true command or that true might be a keyword in bash. | |
| Jun 12, 2022 at 14:05 | comment | added | Tom Shaw | There's a serious exception - the_world_is_flat = true surely would cause the exception stupidity=true to also be false. | |
| Nov 7, 2021 at 20:05 | comment | added | alper |
would it be same if I apply it for false?
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| May 27, 2021 at 12:28 | comment | added | Gauthier |
Not assigning the_world_is_flat first still works as expected. Why? I'd expect the condition evaluation to result in a syntax error.
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| Mar 26, 2021 at 10:03 | comment | added | zaTricky | Doesn't the single = inside the [] need to be doubled == ? | |
| Oct 21, 2020 at 19:17 | comment | added | Jemar Jones | Super casual flat earther comment, nothing to see here | |
| Aug 17, 2020 at 12:46 | review | Suggested edits | |||
| Aug 18, 2020 at 10:00 | |||||
| Apr 6, 2020 at 15:31 | comment | added | tahiche | Note the importance of the space... "if [ "$the_world_is_flat"=true ]" (no space around = operator) will always be true. This gets me every time | |
| May 27, 2019 at 23:27 | history | edited | Gurpartap Singh | CC BY-SA 4.0 |
correct typo: if -> fi
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| May 17, 2019 at 14:13 | history | edited | granadaCoder | CC BY-SA 4.0 |
edited body
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| Jan 4, 2018 at 22:52 | comment | added | Timothy Swan | [[ -e file.txt ]] ; echo "$?" Prints 0 if file is there. This is necessary to include as part of the answer because otherwise people won't know how to store the boolean. | |
| Nov 30, 2017 at 1:15 | comment | added | Levi | @HubertGrzeskowiak "It is executing a command every time you check the value": this is only true for very old shells. true (and false) are built-in commands in bash (and virtually every other shell): no new process is started. | |
| Nov 3, 2017 at 9:12 | comment | added | Hugo G | About the newer answer: it is simple string comparison. When in bash, you should rather use double square brackets and quote everything so people know it's strings and nothing special. | |
| Nov 3, 2017 at 9:11 | comment | added | Hugo G |
DO NOT USE THE ORIGINAL ANSWER! It is executing a command every time you check the value and it's easy to forget how it works and put square brackets around it (which breaks it all). Short answer is: bash does not have booleans. It only has builtin testing ([ ], [[ ]], test) which evaluates to a boolean'ish exit code. You cannot define that boolean, though.
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| Sep 13, 2017 at 12:29 | comment | added | andras.tim |
I think this answer can kill the kitties because the true in the_world_is_flat assignment is a command in the original answer! Let's check with the_world_is_flat=date...
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| May 23, 2017 at 10:31 | history | edited | URL Rewriter Bot |
replaced http://stackoverflow.com/ with https://stackoverflow.com/
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| Dec 13, 2016 at 9:17 | comment | added | Loenix | VAR=true; $VAR && echo "TRUE" || echo "FALSE"; Show True and VAR=false; $VAR && echo "TRUE" || echo "FALSE"; Show False. So this is working properly... | |
| Mar 4, 2016 at 13:41 | comment | added | dolmen | The original answer was just better and completely safe as long as the assignments of the variable are completely controlled inside your script. | |
| Jun 8, 2015 at 23:02 | comment | added | wisbucky | @ajk The reason that a lot of the comments seem incorrect is because miku's original answer was revised by another user on Feb 12, 2014, so it invalidated most of the previous comments. | |
| S Jun 8, 2015 at 22:52 | history | suggested | wisbucky | CC BY-SA 3.0 |
The Revised Answer on Feb 12, 2014 caused a lot of confusion because there were many comments and other answers that referenced the Original Answer. Including the original answer helps the reader understand the context of the older comments and answers.
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| Jun 8, 2015 at 21:32 | review | Suggested edits | |||
| S Jun 8, 2015 at 22:52 | |||||
| Apr 1, 2015 at 9:58 | comment | added | Quolonel Questions | This code is not the same and does not work in the same way as the linked article. The linked code calls a program by the name stored in a variable but the code in this answer is just string comparison. | |
| Jul 9, 2014 at 16:51 | history | edited | miku | CC BY-SA 3.0 |
added 16 characters in body
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| Feb 21, 2014 at 8:58 | history | edited | miku | CC BY-SA 3.0 |
deleted 76 characters in body
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| Feb 20, 2014 at 1:09 | comment | added | ajk | Lots of incorrect information, here. /bin/true isn't being used effectively. See Dennis' answer. | |
| S Feb 12, 2014 at 14:13 | history | suggested | lensovet | CC BY-SA 3.0 |
updating per other answer explaining why the original code here had issues
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| Feb 12, 2014 at 14:12 | review | Suggested edits | |||
| S Feb 12, 2014 at 14:13 | |||||
| Jan 21, 2014 at 13:44 | history | edited | miku | CC BY-SA 3.0 |
added 54 characters in body
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| Jan 18, 2014 at 23:04 | comment | added | Dennis | -1, see my answer for an explanation. | |
| Dec 31, 2013 at 9:10 | history | edited | miku | CC BY-SA 3.0 |
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| Jul 31, 2013 at 12:16 | history | edited | miku | CC BY-SA 3.0 |
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| Jun 30, 2012 at 9:07 | comment | added | michael |
@pms The operators "-o" and "-a" are only for the "test" command (aka "[]"). Instead, this is "if + command", without the "test". (Like "if grep foo file; then ...".) So, use the normal && and || operators: # t1=true; t2=true; f1=false; # if $t1 || $f1; then echo is_true ; else echo is_false; fi; (returns "true", since t1=true) # if $t1 && $f1 || $t2; then echo is_true ; else echo is_false; fi (returns "true", since t2=true) . Again, this ONLY works because "true"/"false" are bash-builtins (returning true/false). You can't use "if $var..." unless var is a cmd (ie, true or false)
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| Sep 7, 2010 at 1:33 | history | edited | miku | CC BY-SA 2.5 |
deleted 1 characters in body
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| Jul 19, 2010 at 5:30 | vote | accept | hassaanm | ||
| Jun 2, 2010 at 4:16 | comment | added | Dennis Williamson |
To explain what is happening: the if statement is executing the contents of the variable which is the Bash builtin true. Any command could be set as the value of the variable and its exit value would be evaluated.
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| Jun 1, 2010 at 21:58 | history | answered | miku | CC BY-SA 2.5 |