cp command - dot or asterisk at end of source directory?

esuhl · 2022-12-02 02:55:03

I want to copy a directory (and all of its contents) to another directory.

In some examples of the cp command, I've seen, a dot(.) or asterisk(*) used at the end of the source location. I've googled and I just can't understand what the dot or asterisk would do compared to omitting them.

So, what is the difference between these commands:

cp -r /dir1/ /dir2/
cp -r /dir1/. /dir2/
cp -r /dir1/* /dir2/

Sorry if this is a dumb question.
Thanks :-)

mpan · 2022-12-02 04:00:44

This is not a `cp` question, as `cp` is not really involved. The asterisk is a feature of your shell, which expands it. `cp` receives the expanded file names. It never sees the asterisk. The same applies to all other commands.⁽¹⁾ Instead of `cp`, use `echo` to understand what arguments a command receives.

If in bash⁽²⁾ you may use this helper function:

printArgs() {
    i=1
    while (( $# )); do
        printf '% 4d: %s\n' "$i" "$1"
        (( ++i ))
        shift
    done
}

A single dot is a special entry in a directory, which links to the directory itself. It’s an entry no different as any sub-directory would be. In a similar fashion two dots are an entry that link to the parent directory.
____
⁽¹⁾ Some commands may accept globs as their arguments, but those must be enclosed in quotes to prevent expansion by the shell.
⁽²⁾ May work in other shells too.

Last edited by mpan (2022-12-02 04:02:26)

HalosGhost · 2022-12-02 04:05:09

[Edit]: mpan got there first and answered excellently.

The asterisk is shell-globbing (it will expand to all the files underneath dir1). Note: it's a bit worrying doing this with `cp` (or `mv`; this isn't specific to `cp) because it can lead to doing something different than you'd expect (potentially leading to data loss; speaking from experience, I have accidentally overwritten files by doing this; just say "No" ).

The very verbose version of what people are hoping the asterisk version of the command will do is a for loop like so:

for i in /dir1/*; do
    cp -r "$i" /dir2/
done

In nix-like operating systems, every directory has two special "files" always present: `.` and `..`. `..` is the given directory's parent directory, and `.` refers to the directory itself.

So, `/dir1/..` just refers to `/` and `/dir1/.` refers to `/dir1`. There should be no practical difference between the first and second examples you list.

All the best,

-HG

cfr · 2022-12-02 04:31:24

HalosGhost wrote:

The asterisk is shell-globbing (it will expand to all the files underneath dir1). Note: it's a bit worrying doing this with `cp` (or `mv`; this isn't specific to `cp) because it can lead to doing something different than you'd expect (potentially leading to data loss; speaking from experience, I have accidentally overwritten files by doing this; just say "No" ).

$ for i in cp mv rm; do type $i; done
cp is aliased to `cp -n'
mv is aliased to `mv -n'
rm is aliased to `rm --one-file-system'

Never forget your fallibility when configuring your shell . For root rm is configured to be interactive, but that would be too inconvenient for day-to-day use.

Edit: also

$ shopt -o
...
noclobber       on
...

Last edited by cfr (2022-12-02 04:36:42)

Trilby · 2022-12-02 04:48:29

FYI, off the primary topic, but `type` can take multiple arguments:

$ type cp mv rm
cp is an alias for cp -i
mv is an alias for mv -i
rm is rm

cfr · 2022-12-02 04:55:47

Trilby wrote:

FYI, off the primary topic, but `type` can take multiple arguments:

Thanks!

Arch Linux

#1 2022-12-02 02:55:03

cp command - dot or asterisk at end of source directory?

#2 2022-12-02 04:00:44

Re: cp command - dot or asterisk at end of source directory?

#3 2022-12-02 04:05:09

Re: cp command - dot or asterisk at end of source directory?

#4 2022-12-02 04:31:24

Re: cp command - dot or asterisk at end of source directory?

#5 2022-12-02 04:48:29

Re: cp command - dot or asterisk at end of source directory?

#6 2022-12-02 04:55:47

Re: cp command - dot or asterisk at end of source directory?

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