My expr is being printed but not evaluated

Question

The code for the script is:

echo "Years:"
read age
x=`expr $age*365`
echo -e $x

The output when I call this script from the command line is as follows:

Years: 

(say I put 20)

20*365

Why is it not evaluating?

Answer 1

expr is archaic and largely obsolete these days. It's also very limited and clumsy to use compared to better alternatives like:

1. bash has integer-only arithmetic built-in these days.

   $ age=20
   $ echo "$((age * 365))"
   7300
   
   $ x=$((age*365))
   $ echo "$x"
   7300
   

2. use bc for floating-point arithmetic:

   $ age=20
   $ echo "$age * 365.25" | bc
   7305.00
   

   Or, if you want to drop the decimal fraction:

   $ echo "scale=0; $age * 365.25/1" | bc
   7305
   

   The division by 1 is needed because addition, subtraction, and multiplication ignore the scale setting in bc. This is a long-standing annoyance and is unlikely to be "fixed".

3. if you prefer RPN, you could use dc:

   $ age=20
   $ dc -e "$age 365.25 * p" 
   7305.00
   

Note: backticks are obsolete and deprecated too. Use $(...) instead of backticks. e.g.

x=$(echo "$age * 365.25" | bc)

x=$(dc -e "$age 365.25 * p")

Answer 2

we should escape the special character * and keep spaces between values and operator.

Try as,

x=`expr $age \* 365`