Good question, you can of course test this yourself with `time`. In the case of Bash, non-built-in commands are stored in a lookup table, exposed via the hash

Good question, you can of course test this yourself with `time`. In the case of Bash, non-built-in commands are stored in a lookup table, exposed via the hash built-in (`help hash`). So, there should only be a one-time performance hit per shell instance. Generally speaking, stat'ing hundreds of directories is surprisingly quick, most binaries do it all the time, when loading libraries for example. You can `strace` to see the numerous file tree crawls.