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In many scripts I've inherited from a former employee I keep seeing this pattern:
if (true $SOME_VAR)&>/dev/null; then ... fi or this one
(true $SOME_VAR)&>/dev/null || SOME_VAR="..." The man page for true says it always returns true, hence I keep wondering, what is the point of these checks? In the first case the then part is always executed, in the second case the right hand part is never executed.
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The true and false commands Wherever you see true or false in Bash, it's either a string or a command/builtin which is only used for its exit code. where the command is true . The condition is true whenever the command returns exit code 0.
There are no Booleans in Bash. However, we can define the shell variable having value as 0 (“ False “) or 1 (“ True “) as per our needs.
On Unix-like operating systems, the true command's sole purpose is to return a successful exit status. It is useful when you want part of a command or conditional expression always to be true.
Using true and false As you can see, true simply returns a 0 and false simply returns a 1. Probably the most common use of the true command is to start an infinite loop. Instead of starting a loop with a command like while [ $num -le 12345678 ], you can use while true and the loop continues until you stop it will a ^c.
If set -u (a.k.a. set -o nounset) is in effect, true $SOME_VAR will fail when $SOME_VAR is not defined. This is therefore a way to test whether the variable is defined.
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