BASH: Factorial using FOR loop not working

Shell Programming and Scripting
1

Hi,

I am trying to run the factorial script but it�s not working.

The code is mentioned below:
------------------------------------------------------------------

/home/gc> cat fact.sh
#!/bin/bash
# using one command line parameter
 
factorial=1
for (( number = 1; number <= $1 ; number++ ))
do
factorial=$[ $factorial * $number ]
done
echo The factorial of $1 is $factorial

------------------------------------------------------------------
Execution:

/home/gc> bash -x fact.sh 5
+ factorial=1
fact.sh: syntax error near unexpected token `(('
fact.sh: fact.sh: line 5: `for (( number = 1; number <= $1 ; number++ ))'

------------------------------------------------------------------

Can anyone please help?

Regards,
GC

---------- Post updated at 09:33 PM ---------- Previous update was at 06:32 PM ----------

Ok, I've got the reason; it's the bash shell version. I was running the script in an old bash version. I found a link where this was stated. It was mentioned that 'seq' command can be used instead but even that is not recognized on my bash.

I am using GNU bash, version 1.14.5(1)

Can anyone suggest some alternative?

Regards,
GC

2

You were really close. For arithmetic, use parentheses, not brackets:

(12:40:19\[D@DeCoBox15)
[~]$ cat fact
#!/bin/bash
# using one command line parameter

factorial=1
for (( number = 1; number <= $1 ; number++ ))
do
factorial=$(($factorial * $number))
done
echo The factorial of $1 is $factorial

(12:40:21\[D@DeCoBox15)
[~]$ bash fact 12
The factorial of 12 is 479001600
3

seq is not a bash feature, but an external command. Apparently, your system does not have it. Perhaps you can try jot. Alternatively, you can use a while loop:

f=1 i=1
while [ $i -le $1 ]; do
    f=$((f*i))
    i=$((i+1))
done
echo $f

Regards,
Alister

4

Thanks DeCoTwc & alister for your inputs!

@DeCoTwc: I tried your method but those braces also did not work. I got a similar error message.

/home/gc> bash unix1_fact.sh 5
 unix1_fact.sh: syntax error near unexpected token `(('
 unix1_fact.sh: unix1_fact.sh: line 5: `for (( number = 1; number <= $1 ; number++ ))'

Looks like the bash I am trying on is too old to understand even your suggested syntax. :slight_smile:

I tried the same code on newer bash and it worked fine. Anyways, thanks for your input.

@alister: Your method was working fine. Thank You!

I also tried awk; it also works fine on my old bash version.

Regards,
GC