In Conda's manual for Travis integration, what does hash -r do and is it necessary?
hash is a bash builtin. hash -r will rescan the $PATH for available executable commands, so Bash knows what to execute when you type a command name.
According to man bash, if type in a command, Bash will first search its internal data structure for which command to execute. If that fails, it will make a search in the $PATH.
It seems to me that this call to hash -r is unnecessary.