Source code in the unix programming language

factorial() {
  set -- "$1" 1
  until test "$1" -lt 2; do
    set -- "`expr "$1" - 1`" "`expr "$2" \* "$1"`"
  done
  echo "$2"
}

function factorial {
  typeset n=$1 f=1 i
  for ((i=2; i < n; i++)); do
    (( f *= i ))
  done
  echo $f
}

factorial ()
{
  if [ $1 -eq 0 ]
    then echo 1
    else echo $(($1 * $(factorial $(($1-1)) ) ))
  fi
}

function factorial {
  typeset n=$1
  (( n < 2 )) && echo 1 && return
  echo $(( n * $(factorial $((n-1))) ))
}

alias factorial eval \''set factorial_args=( \!*:q )	\\
	@ factorial_n = $factorial_args[2]		\\
	@ factorial_i = 1				\\
	while ( $factorial_n >= 2 )			\\
		@ factorial_i *= $factorial_n		\\
		@ factorial_n -= 1			\\
	end						\\
	@ $factorial_args[1] = $factorial_i		\\
'\'

factorial f 12
echo $f
# => 479001600