I am learning Shell Scripting and i got stuck that in most languages like C,C++, 0 means false and 1 means true, but in below shell script I am not able to understand, how the output is generated
if [ 0 ]
then
echo "if"
else
echo "else"
fi
No matter what i write inside if block like instead of 0, I tried 1,2,true,false it is always running if condition. How this works in shell scripting. And what shell script returns when the expression inside if statement is false.
It is always executing if part because this condition:
[ 0 ]
will always be true as it checks if the string between [ and ] is not null/empty.
To correctly evaluate true/false use:
if true; then
echo "if"
else
echo "else"
fi
10 -gt 100 is a valid shell test condition and it will evaluate to falseThere are no booleans in Bash. But here are some examples that are interpreted falsy:
A 0 as in your example is not falsy, because it's a non-empty value.
An example with empty value:
if [ "" ]
then
echo "if"
else
echo "else"
fi
An example with non-zero exit code (assuming there's no file named "nonexistent"):
if ls nonexistent &> /dev/null
then
echo "if"
else
echo "else"
fi
Or:
if /usr/bin/false
then
echo "if"
else
echo "else"
fi
Or:
if grep -q whatever nonexistent
then
echo "if"
else
echo "else"
fi
