shell - using expr "multiplication table"

Question

I'm learning shell to create a multiplication table, I write code like that:

#!/ in/bash
for i in 1 2 3 4 5 6 7 8 9
do
 for j in 1 2 3 4 5 6 7 8 9
 do
 if [ $j -le $i ]
 then
 echo -ne "$i"X"$j"=`expr "$i"*"$j"` "\t"
 else
 echo
 break
 fi
 done
 done
echo -ne "\n"

however I get the response in console like that:

1X1=1*1
2X1=2*1 2X2=2*2
3X1=3*1 3X2=3*2 3X3=3*3
4X1=4*1 4X2=4*2 4X3=4*3 4X4=4*4
...

I hope the answer is like that "1x1=1, 2x1=2 ...". Could anyone tell me how to modify this code?

• Jeff Schaller: Or put a space around the * operator
• steeldriver: ... and escape/quote it I think e.g. expr "$i" \* "$j"

Answer 1

Yes, you can use bash's built-in Arithmetic Expansion $(( )) to do some simple maths.

For Multiplication:

echo $(( 6 * 7 ))

Result

42

And your script would look like this:

#!/ in/bash
for i in 1 2 3 4 5 6 7 8 9
do
 for j in 1 2 3 4 5 6 7 8 9
 do
 if [ $j -le $i ]
 then
 echo -ne "$i"X"$j"=$(($i * $j)) "\t"
 else
 echo
 break
 fi
 done
 done
echo -ne "\n"

Answer 2

Simplifying the solution a bit, by removing an unnecessary test:

#!/bin/bash
for (( i = 1; i < 10; ++i )); do
 for (( j = 1; j <= i; ++j )); do
 printf '%dx%d=%-2d ' "$i" "$j" "$(( i * j ))"
 done
 printf '\n'
done