Explaining Logical Operators (&& and ||) in Bash

The aim of this page📝 is to present the value of logical operators AND && and OR || in bash conditionals.

$ false && echo howdy! 
<NOTHING>
$ true && echo howdy!
howdy!
$ true || echo howdy!
<NOTHING>
$ false || echo howdy!
howdy!

hAIku: In Picasso’s hand,
Conditional paths converge
scripts unfold art

1. def: left and right

• the right side of && will only be evaluated if the exit status of the left side is 0 (i.e. true).
• the right side of || will evaluate only if the left side exit status is non-0 (i.e. false).

2. use: for oneliners

• use the && and || to reduce an if statement to a single line with the help of a conditional expression
• and potentially, for validation methods/subfunctions that are often present right after the beginning of the function
• say we are looking for a file called /root/Sample.txt then the traditional iteration would be as follows in shell

if [[ -f /root/Sample.txt ]]; then
    echo "file found"
else
    echo "file not found"
fi

• These 6 lines can be reduced to an oneliner

[[ -f /root/Sample.txt ]] && echo "file found" || echo "file not found"

• The given one-liner can be seen as a shorthand for an if-else statement, with the format <predicate> && <consequent> || <alternative>.
• While you can simulate an if-elif-else structure using conditional operators, it's generally recommended to use a proper if-elif-else for clarity and maintainability.

Still, Example of using more elaborate conditional operators:

[[ -f /root/Sample.txt ]] && echo "file found" || 
    { [[ -d /root/Sample.txt ]] && echo "a directory found" || 
        echo "neither file nor directory found"; }

3. links

• https://unix.stackexchange.com/questions/24684/confusing-use-of-and-operators
• https://unix.stackexchange.com/a/291020/498388