I am not able to find much about it's origin or who created it and am curious as to why a full stop was chosen to represent this command.
The earliest mentioning of the dot command that I can find is in the manual for Stephen Bourne's
sh shell in Unix Release 7 (it may be older, but not evidently present as one of the built-in commands in
sh in Release 6).
. file Read and execute commands from file and return. The search path $PATH is used to find the directory containing file.
The dot, in quite general terms, seems to have been associated with "here" or "current". The
. directory is the current directory, and the
. address in the
adb debugger from the same release of Unix had a
. address which was the current address. Likewise, entering a
. followed by newline in the
ed editor will re-display the current line of the editing buffer (
. addresses the current line). The dot also means the current node in certain structured query languages for XML, JSON, YAML, etc. (although these are later inventions).
It is therefore, I think, not too far fetched to speculate that the
. command in the shell also means "here" or "current". In particular, "run this script in the current environment."
The dot is also quite quick and easy to type, and having a short command for doing a common task (whether it be in
adb or in the shell) may have been another reason why another longer name was not used.
Note that I don't have a functioning version of
sh from Release 7 to test things in, and that I can't find the actual implementation of
. in Bourne's shell from that release in the above-mentioned Git repository, so I can't say for sure that it actually did exactly what it does today. But it's likely that it did.
May it be because
dot is the name of the symbol