How should I phrase an if statement with multiple conditions:
if [ <T/F Condition> ] && [ <T/F Condition> ] && [ <T/F Condition> ]
or
if [ <T/F Condition> && <T/F Condition> && <T/F Condition>]
?
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Does this answer your question? How to represent multiple conditions in a shell if statement?Shawn– Shawn2021-02-20 20:40:12 +00:00Commented Feb 20, 2021 at 20:40
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2 Answers
As "man test" would've shown you "-a" stands for "and".
eg.:
if [ <T/F Condition> -a <T/F Condition> -a <T/F Condition> ]
Watch the spacing too.
7 Comments
Gerard H. Pille
I didn't. Why do you think so? "[" is a link to "test".
Shawn
@djifan23 He's correcting your syntax for your second snippet. But see mywiki.wooledge.org/…
Gerard H. Pille
@Shawn That link got me WTF'ing, until I read the comments. ;-)
Shawn
? It seems straightforward... And what comments?
Gerard H. Pille
If you follow the link, the first thing you see is an invalid statement. A lot of emphasis on what you should NOT do.
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The && is a shell operator, in cmd1 && cmd2, it tells the shell to only run the second command if the first succeeds.
So, this works, and does what you want:
if [ "$x" = a ] && [ "$y" = b ]; then ...
However, in this:
if [ "$x" = a && "$y" = b ]; then ...
The commands to run would be [ "$x" = a and "$y" = b ], the first of which will give an error for the missing ] argument. (Here, it's good to remember that [ is a regular command, similar to echo or so, it just has a funny name.)
Also, you should avoid this:
if [ "$x" = a -a "$y" = b ]; then ...
even though it works in some shells in simple cases. This has to do with parsing issues when the variables contain strings like ! (negation) or others that are operators for [. Again, since [ is a regular command, and not special shell syntax, it can't tell which arguments come from variables and which are hardcoded operators.
