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Computational Techniques for Life Sciences

Subprograms/Subfunctions

Purpose

create reusable blocks of bash commands

Syntax

function_name () {
commands.... ;
return ;
}

prompt> print_something () {
   echo Hello you typed $1 ;
   return 1 ;
}
prompt> print_something frog
Hello you typed frog
prompt> print_something toad
Hello you typed toad

EXERCISE:

Create a script that recursively uses a subfunction to calculate factorials but stops if you enter 0.

prompt> vi factorial.sh

#!/bin/sh

factorial()
{
  if (( "$1" > "1" )) ; then
    i=$(( $1 - 1 ));
    j=$(factorial $i )
    k=$(($1 * $j))
    echo $k
  else
    echo 1
  fi
}


while :
do
  echo "Enter a number:"
  read x
  if (( $x == 0 )); then break ; fi;
  factorial $x
done  

prompt> ./factorial.sh
Enter a number:
5
120
Enter a number:
4
24
Enter a number:
0
prompt>