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I know that bash doesn't support boolean variables, so how do people typically represent a value that needs to be used later, and that can be truthy or falsey? From this question, some ways seem to be calling out to the true/false programs via a variable, doing string comparison in an if, and using a case statement. Are these what bash programmers commonly use, or are there other methods I'm not considering?

Christopher Shroba
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    Does this answer your question? [How can I declare and use Boolean variables in a shell script?](https://stackoverflow.com/questions/2953646/how-can-i-declare-and-use-boolean-variables-in-a-shell-script) – Ari Fordsham Sep 13 '20 at 14:11
  • Note that true and false are builtin commands, so there's no performance penalty for using them. – glenn jackman Sep 13 '20 at 20:13

1 Answers1

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Just expanding the ideas in your question:

the true/false commands

bool=true

if $bool; then echo Y; else echo N; fi   # => Y

string value

bool="yes"

if [[ $bool == "yes" ]]; then echo Y; else echo N; fi   # => Y

string emptiness

bool=""

if [[ $bool ]]; then echo Y; else echo N; fi   # => N

zero/non-zero integer

bool=0

if ((bool)); then echo Y; else echo N; fi   # => N

There's also a form using the boolean control operators:

((bool)) && echo Y || echo N

You have to be a bit careful with A && B || C -- C will execute if either A or B fails.

With if A; then B; else C; fi the only time C runs is if A fails, regardless of what happens with B.

Given

A() { echo A; }
B() { echo B; return 1; }
C() { echo C; }

Then

$ A && B || C
A
B
C

$ if A; then B; else C; fi
A
B
glenn jackman
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