How do I echo a sum of a variable and a number?

Question

I have a variable x=7 and I want to echo it plus one, like echo ($x+1) but I'm getting:

bash: syntax error near unexpected token `$x+1'

How can I do that?

Answer 1

No need for expr, POSIX shell allows $(( )) for arithmetic evaluation:

echo $((x+1))

See §2.6.4

Answer 2

echo $((x+1)) also same result as echo $(($x+1))

Answer 3

You can also use the bc utility:

$ x=3;
$ echo "$x+5.5" | bc
8.5