Stephen Bourne wrote the Bourne shell (sh) at Bell Labs in 1979, replacing the earlier Thompson shell with something that had variables, control flow, and a vaguely programmable syntax. It became the standard Unix shell and the ancestor of essentially every POSIX-compatible shell since. The C shell (csh) arrived from BSD around the same time and immediately started an argument about syntax that has never fully resolved. Then came the Korn shell, then bash (the Bourne-Again Shell, a name that manages to be simultaneously a pun, a tribute, and a dig), then zsh, then fish, then various others with opinions about prompts. Every Unix system ships /bin/sh pointing at something claiming Bourne compatibility. What it actually points at varies by distro, has broken countless scripts, and is the reason every serious shell script begins with an explicit shebang rather than trusting the system to guess correctly.
