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Evaluate condition.
TLDR
Test if a given variable is equal to a given string
$ [ "[$VARIABLE]" == "[/bin/zsh]" ]
Test if a given variable is empty
$ [ -z "[$GIT_BRANCH]" ]
Test if a file exists
$ [ -f "[path/to/file]" ]
Test if a directory does not exist
$ [ ! -d "[path/to/directory]" ]
If-else statement
$ [ [condition] ] && [echo "true"] || [echo "false"]
