Conditionals and Tests

Part of the Bash course

Every script you have written so far runs the same lines no matter what. Real scripts need to make decisions: "only do this if that file exists", "only continue if the last command worked". This lesson teaches you how Bash asks those questions and acts on the answer. Nothing here assumes you have written a decision-making program before.

In lesson 02 you met the exit code: a hidden number every command produces when it finishes, where 0 means success and anything else means failure. Conditionals in Bash are built entirely on that idea. Where other languages ask "is this true or false?", Bash asks "did this command succeed or fail?" and treats success as yes: if does not look at a value, it runs a command and reacts to whether its exit code was 0. ...