bash is a widely-used command interpreter. It performs all kinds of expansions and substitutions on a given command line before executing it, thus making this interpreter a powerful tool. bashbug is a shell script to help the user compose and mail bug reports concerning bash in a standard format. sh is a symlink to the bash program. When invoked as sh, bash tries to mimic the startup behavior of historical versions of sh as closely as possible, while conforming to the POSIX standard as well.