How does the keyword “if” test if a value is true or false?

Question

In bash script

if [ 1 ]
then
   echo \"Yes\"
else
   echo \"No\"
fi

Output: Yes

It

Answer 1

The return value of a command is checked. [ 1 ] has a return value of 0 (true). Any other return value (like 1) indicates an error.

You can display the return value of the last executed command using the $? variable:

true
echo $?
# returned 0
false
echo $?
# returned 1
echo $?
# returned 0 as the last executed command is 'echo', and not 'false'