Why does this compound command report errors when copying directories? [duplicate]

Question

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Why does this compound command report errors when copying directories?

if one executes the following two commands in one line, as follows,

rm -rf dir ; cp -r dir2 dir

it may complain that cp can not create directory dir/subdir: File exists

but if these two commands are executed in two lines, no errors will be thrown. I am just wandering what is the difference? and more importantly, how to execute two commands in one line, with the effect exactly the same as by two lines...

PS: what is in dir or dir2 is hugh, typically 4gb

Answer 1

You can use '&&' to concatenate commands. It runs the next command if the first was succesful.

rm -rf dir && cp -r dir2 dir