arithmetic operation with expr

Question

I am doing add operation as

#!/bin/sh
a=10
b=20
c='expr $a + $b'
echo "$c"
echo "$a"
echo "$b"

but it is showing output as

expr $a + $b
10
20

what is wrong with expr

Answer 1

Your example uses the wrong type of quotes:

a=10 b=20 c='expr $a + $b' echo "$c" echo "$a" echo "$b"

which should be (as a start):

a=10
b=20
c=`expr $a + $b`
echo "$c"
echo "$a"
echo "$b"

but more readable:

a=10
b=20
c=$(expr $a + $b)
echo "$c"
echo "$a"
echo "$b"

If you want to put all of those statements on a single line, separate them by semicolons:

a=10; b=20; c=$(expr $a + $b); echo "$c"; echo "$a"; echo "$b"