Question

I’m trying to write a simple little script to query a 3g connection, and if the connection has dropped, instigate a reconnection.

My problem is in checking the output of the command – two seemingly equal strings are not evaluated as equal. I’m sure there’s a noob error in here somewhere!

#!/bin/bash

echo "Checking connection"
a="Not connected."
b=$(./sakis3g status --console)

if [[ "$a"!="$b" ]]; then 
    echo "Strings not equal:"
    echo "$a"
    echo "$b"
else 
    echo "Strings equal!!"
fi

The output when run:

user@mypc:~$ ./test_3g.sh 
Checking connection
Strings not equal:
Not connected.
Not connected.

When running ./test_3g.sh | cat -A:

user@mypc:~$ ./test_3g.sh | cat -A
Checking connection$
Strings not equal:$
Not connected.$
Not connected.$

Answer 1

You have to put spaces around operators:

if [[ "$a" != "$b" ]]; then ...

Without spaces you end up with a single string, equivalent to "$a!=$b". And testing just a string returns true if that string is non-empty…