Question

In bash script

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

Output: Yes

It represents that ‘1’ is treated as true value.

But in code:

word = Linux
letter = nuxi
if echo "$word" | grep -q "$letter"
then
    echo "Yes"
else
    echo "No"
fi

Output: No

But echo "$word" | grep -q "$letter" will return 1, so why is the result is No.

How does the keyword if test the value returned by the command after if?

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'