Input Positional Parameters

Script files can take parameters (arguments) just like Linux and Bash commands.

Example 1:
./mycopy.sh soure_file desitnation_file
cat mycopy.sh
#!/bin/bash
# use interactive copy so as to not write over a file.
cp -i $1 $2

Example 2 - Shift Parameter Iteration
./shift_iteration.sh Paul Mary John
cat shift_iteration_shift.sh
#!/bin/bash
while (( $#>0 ))  # while number of parameters > 0
do
  echo $1
  shift      #shift paramters left by one and decrement #
done

Example 3 - Parameter Iteration
./script_iteration.sh Paul Mary John cat script_iteration.sh
#!/bin/bash
for x in "$@"
do
  echo $x
done
 
You must have double quotes around "$@" for it to handle parameters with spaces correctly ie "pass word". Using shift and iterating over the parameters does not require double quotes even when the parameters contain spaces.

Misinformation & Bad Programing Practices
The Internet is full of misinformation and bad programing practices on how to use positional parameters. It is common to see examples where they are using shift and testing the length of the parameter. They are testing an unset parameter! Which can result in an infinite loop. To make this work, they place double quotes around the parameter, which insures it is a string. For example:
 
while [-n "$1"]
 
Just google "double quotes around positional parameters". It's a mess that should be avoided. In the end, they end up putting double quotes around everything.
 
The following is from the "Real-world example" at: https:/www.computerhope.com/unix/bash/shift.htm
 
while (( "$#" )); do   # this should be: while (( $# )); do
 
and from the same example:
 
if [ "$#" == "0"]; then;   # this should be: if (( $# == 0 )); then
 
The following is from: http://www.shellscript.sh/variable2.html":
 
while [ "$#" -gt "0" ];   # -gt should be used with intergers not strings
 
And there are coutless code examples that use:
 
echo "$1"   # when $1 is already a string.

• References:
• What is $* and $# in Linux?
• Shell Programming
• Space in Java command-line arguments
• Positional Parameters tests for unset parameters
• What does ${1+"$@"} mean?
• Quoting in Shell Programing

Options

Script can also have options that determine how the script operates e.g ls -l says to list the files in the long format. By convention, opitions are preceded by a dish, - ,.

options_example.sh
#!/bin/bash
if [ -z "$1" ]
then # no options specified
 echo "This commands requires a -a or -b option"
else
  for x in "$@"
  do
  case $x in
   -a) echo "-a option" ;;
   -b) echo "-b option" ;;
   *) echo "invalid option - valid options are -a and -b" ;;
  esac
 done
fi

Also by bash convention, options should come before parameters and a -- seperates options from parameters i.e.
script_file options -- parameters

options_with_parameters.sh
#!/bin/bash
until [ "$1" = -- ]
do
 case $1 in
   -x) echo "option -x" ;;
   -y) echo "option -y" ;;
   -z) echo "option -z" ;;
   *) echo "invalid option" ;;
 esac
 shift
done
 
shift # get past --
x=1
for y in "$@"
do
  echo "parameter $x is $y"
  x=$[ $x+1 ]
done

To process catenated options e.g -alh, you have to use getopt and/or getopts.
Add to this -

--
bash command: set -- . If no arguments follow this option then the positional paramaters are unset. Otherwise the positional paramaters are set to the args, even if some of them begin with a -.