Complex Conditionals

In the potion script, a variable called RESP is tested. If it is, then the program provides instructions. One way to do this is fairly brittle:

if [ "$RESP" = "y" -o "$RESP" = "Y" -o "$RESP" = "Yes" -o "$RESP" = "yes" ]

If the RESP matches y or Y or Yes or yes, then it'll do one thing. If the response is anything else, the program provides different instructions. For example, if you answered YES, you would get different instructions, so the system is actually fairly brittle.
It is possible to use regular expressions (regex) to provide greater flexibility:

if [[ "$RESP" =~ [yY]|[yY][eE][sS]]

Here's how to unpack this statement:
[yY] If the answer is y or Y
| pipe operator means OR
[yY][eE][sS] If the answer includes any combination of 'yYeEsS'

This is less brittle but will match weird answers like 'yyy' or 'sey'
Visit regexr to play with regular expressions

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Practicum: Bash Scripts 3: Understand Bashcrawl (~60-minutes)