Product of a digit with a shell script - bash

Question

How do I get the product of a 1 number in bash? (12345 > 1x2x3x4x5)
I am trying to get a script to do multiplication, I have tried escaping the * char but no luck, I have also tried fiddling with expr.
echo -n "Enter number "
read n
len=$(echo $n | wc -c)
len=$(( $len - 1 ))
for (( i=1; i <= $len; i++ ))
do
prod=$(($prod \* $(echo $n | cut -c $i) ))
done
echo "Product of $n is $prod"

Answer 1

You can get the length of a string from parameter expansion, no need to call external tools.
#!/bin/bash
read -p 'Enter number: ' n
product=1
for (( i=0; i < ${#n}; ++i )) ; do
d=${n:i:1}
(( product *= d ))
done
printf '%d\n' $product
And, for fun, using Perl:
perl -MList::Util=product -le 'print product(split //, shift)' -- "$n"

Answer 2

gawk (GNU awk) solution:
echo 12345 | awk -v FPAT="[0-9]" '{ r=$1; for(i=2;i<=NF;i++) r=r*$i }END{ print r }'
The output:
120
FPAT="[0-9]" - represents field value so that each field contains a digit

Answer 3

As I understood you want to get value of digits multiplication in number
Suppose you have number:
number=12345
You have to insert * between digits:
echo $number | sed 's/\([0-9]\)/\1*/g'
We will get string:
1*2*3*4*5*
We don't need last asteriks - let's remove it:
echo $number | sed 's/\([0-9]\)/\1*/g' | sed 's/.$//g'
We will get this:
1*2*3*4*5
We can now redirect it to calc:
echo $number | sed 's/\([0-9]\)/\1*/g' | sed 's/.$//g' | calc -p
It's stdout is:
120

Answer 4

\* is wrong in an arithmetic expression, it should be * alone. But even then running your code gives:
$ bash product.sh
Enter number 12
product.sh: line 10: * 1 : syntax error: operand expected (error token is "* 1 ")
Product of 12 is
The reason for the error is that $prod variable is not set to an
initial value before so it's expanded to an empty value, for example
try it in your terminal:
$ echo $prod
$
In your script you should set prod to an initial value before using
it for the first time. It should be:
echo -n "Enter number "
read n
len=$(echo $n | wc -c)
len=$(( $len - 1 ))
prod=1
for (( i=1; i <= $len; i++ ))
do
prod=$(($prod * $(echo $n | cut -c $i) ))
done
echo "Product of $n is $prod"
There are a few more problems with your code:
always put a shebang line at the top
always double quote the variables
using $ on variables is not necessary in arithmetic expressions in Bash