5-9-Writing-Programs.md

5.9 Writing Programs

5.9.5 Exercises

Below this list of exercises you can find examples of how the programs described here should work when used on the command line.

1. Make a script executable.

2. Put that script in a directory that you create and make that directory part of your PATH.

3. Write a program called range that takes one number as an argument and prints all of the numbers between that number and 0.

4. Write a program called extremes which prints the maximum and minimum values of a sequence of numbers.

$ range 6

## 0 1 2 3 4 5 6

$ range -3

## -3 -2 -1 0

$ extremes 8 2 9 4 0 3

## 0 9

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Solutions

1. Suppose we have a script named script_name.sh in the home directory:

   • Method 1: Valid for the current shell session

   Write this in the shell:

   source script_name.sh

   • Method 2: Valid forever

   Write this in the ~/.bash_profile or ~/.bashrc

   source script_name.sh

   Then, write this in the shell

   source ~/.bash_profile # or ~/.bashrc

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2. Making the script directory a part of PATH:

   mv script_name.sh my_dir/script_name.sh
   
   export PATH=my_dir:$PATH
   
   source ~/.bash_profile # or ~/.bashrc

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3. range

   function range
   {
       local arr=($(eval echo {0..$1}))
   
       echo ${arr[*]}
   }
   
   # Test:
   # range $1
   # or source your script and call in the command line

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4. extremes

   function extremes
   {
       local min=$1
       local max=$1
   
       for i in $@
       do
           [[ $i -lt $min ]] && let min=$i
           [[ $i -gt $max ]] && let max=$i
       done
   
       echo $min $max
   }
   
   # Test:
   # extremes $@
   # or source your script then call in the command line