Functions

• You can also define functions

# Definition:
function foo ()
{
    echo "Arguments work just like script arguments: $@"
echo "And: $1 $2..."
    echo "This is a function"
    returnValue=0    # Variable values can be returned
    return $returnValue
}
# Call the function `foo` with two arguments, arg1 and arg2:
foo arg1 arg2
# => Arguments work just like script arguments: arg1 arg2
# => And: arg1 arg2...
# => This is a function

• More than 9 arguments are also possible by using braces, e.g. ${10}, ${11}, ... or simply

bar ()
{
    echo "Another way to declare functions!"
    return 0
}

• Call the function bar with no arguments:

bar # => Another way to declare functions!

• Calling your function

foo "My name is" $Name

Adding Choices (Options) to Script with case Statements

• Simplify complex conditionals options for multiple different choices

• Using the case statement instead of nested if statements will help your scripts to be readable and easier to maintain

# General format starts with keyword, case, followed by some, EXPRESSION, i.e. string/variable
case EXPRESSION in

    PATTERN_1)  # some pattern terminated by, ')'
        STATEMENTS # if EXPRESSION == PATTERN_1 do this
    ;; # end 

     PATTERN_2) # different pattern terminated by, ')'
        STATEMENTS # if EXPRESSION == PATTERN_2 do this
    ;; #end

    PATTERN_N) # another pattern
        STATEMENTS 
    ;; #end

    *) # default patter
        STATEMENTS # usually "Usage:"
    ;; # end
esac # Ends with esac keyword (case backwards)

Example: Script Checking File Formats in Current Directory

• Use vi to make a new script called, fileformat.sh

• Copy the following lines to the new script using Insert Mode

• Save the file with :wq

• Run script by typing bash fileformat.sh in the terminal

#!/bin/bash

# For each item in stdout of, ls, command
for file in $(ls); do
    Extension=${file##*.} # Assign to variable, Extension
    case "$Extension" in
    sh) 
        echo "Shell script: $file"
    ;;
    md) 
        echo "A markdown file: $file"
    ;;
    png) 
        echo "PNG image file: $file"
    ;;
    txt) 
        echo "A text file: $file"
    ;;
    zip) 
        echo "An archive: $file"
    ;;
    conf) 
        echo "A configuration file: $file"
    ;;
    py) 
        echo "A Python script: $file"
    ;;
    *) 
        echo "Unknown file type: $file"
    ;;
    esac
done