The A-Z of Programming Languages: Bourne shell, or sh

"The primary problem was to design the shell be a fully programmable scripting language that could also serve as the interface to users typing commands interactively at a terminal.

"First of all, it needed to be compatible with the existing usage that people were familiar with. There were two usage modes. One was scripting and even though it was very limited there were already many scripts people had written. Also, the shell or command interpreter reads and executes the commands you type at the terminal. And so it is constrained to be both a command line interpreter and a scripting language. As the Unix command line interpreter, for example, you wouldn't want to be typing commands and have all the strings quoted like you would in C, because most things you type are simply uninterpreted strings. You don't want to type ls directory and have the directory name in string quotes because that would be such a royal pain. Also, spaces are used to separate arguments to commands. The basic design is driven from there and that determines how you represent strings in the language, which is as un-interpreted text."

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