Question

I want to verify if I can connect to a database (PostgresSQL) into a bash script

I execute the following command (PGUSER, PGDATABASE… are set)

 psql -f sql/test_connection.sql > /dev/null 2>&1

When I echo $? it shows 0 if success, 2 if not.

It works fine in a terminal.

When I put it into a bash script the result is always 0 even when the credentials are not correct.

psql -f sql/test_connection.sql > /dev/null 2>&1

if [ $? ]
then
   echo "OK"
else
   echo "Doudh!!"
fi

Where am I missing something ?

Answer 1

Note that if you just pass $? to test (another name for [), that will expand to the string 0 or 2 depending on whether the command was successful. When test is passed a string it just tests if the string is non-empty. In this case, it will always return 0 (true), as both of those strings are non-empty.

What you probably want to do is just use the return value of psql as the argument to if directly, without having to refer to it using $?:

if psql -f sql/test_connection.sql > /dev/null 2>&1
then
   echo "OK"
else
   echo "Doudh!!"
fi

Or, you could test $? against 0 directly

if [ $? -eq 0 ]
then
   echo "OK"
else
   echo "Doudh!!"
fi