Why does cp need -r flag to copy "recursively"? Why doesn't cp automatically copy directories recursively? Would that make more sense?
Is there some documentation that explains this decision? Why do I have to add this flag for cp to do what it should do by default?
Like many other details of Unix commands, this is probably historical. In Unix, cp never supported recursive copies; instead, a specific recursive cp, rcp, was added in V8, replaced later by reccp.
cp -r appeared in 4.2BSD, in 1983. By that time, the behaviour of cp on directories without -r was well defined and it’s possible that some tools relied on cp failing if the source is a directory. Changing that would have broken this expectation.
See the rationale in the cp specification in POSIX for additional discussion of -r and -R.
cp -r was removed from the standard!! Is the equivalent cp -PR now?
-aas default option for everything. Then, no need-r. You can even use an alias:alias cp='cp -a'alias rm='rm -rf', of course, but still holds - please alias it tocpaor some other short mnemonic, but notcpitself.