Scripts with conditionals

Learning outcomes:

• Write and test a script with a conditional and explain the use of conditionals
• Demonstrate how to debug a script with conditionals

Would you like to download my PowerPoint to follow along?

• Basic If-Then-Else loop
• Conditionals mean you have choices in a path, this is not the same as a loop

 
                    if [condition]
                    then
                    echo 
                    yes
                    
                    else
                    echo "no"
                    
                    fi 

• if [ $answer = “Y” ] Brackets do test (can also use function test)
• There are some required pieces of syntax such as "then" that are needed for an if statement
• echo “Yes” If condition is true (can be multiple statements)
• echo “No” If condition is false (can be multiple statements)
• fi End of conditional (if backwards) is used to indicate the if statement has ended
• if statements can also be nested if you wish to have multiple paths, be careful though! A nested if is NOT the same as two if statements next to each other.
• if statements in bash in more detail with some examples
• Case Statements
• Another kind of conditional. This is still a way of indicating paths and choices, not loops, but has differnt syntax.
• If statements can be used to evaluate if one thing has happened, or if you include if-then-else two choices, but they can also include multiple choices by using the if-elseif-elseif...-else
• Case statement example in bash with a comparison to if-else statements
• Conditional statement options
• Tests for string comparison use "="

 string = string

• Test for numbers (-eq -le -ge -gt -lt )

14 -eq 14

• You can also have file test operators such as -e and -s

-e /path/path/file

• Examples of both string and number test operators including sample code
• Debugging and common mistakes
• Space matters (there and not there, can be picky)
• Make sure the condition is right type (-eq vs = vs -f)
• Watch for closing fi
• Some troubleshooting tips

Suggested Activities and Discussion Topics:

• Watch This Video on conditionals with scripting and follow along

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