is there an “undo” command on the unix comand line?

Question

i get the feeling i'm gonna need it one day, like if i've just deleted something i shuldn't have, or renamed something and can't remember what it should be called etc.

Answer 1

Negative. There is no magic undo button in linux.

Answer 2

No.

Unix doesn't natively provide an undo feature. The philosophy is that if it's gone, it's gone. If it was important, it should have been backed up.

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Instead of removing a file, you can move it to a temporary “trash” directory. Some desktop environments make their “delete” command move the file to the trash. But beware that only a few applications will use it; others will just remove the file.

Many commands can be reversed, e.g., a file move can be undone by moving the file back. Commands that delete or overwrite a file can't easily be undone if at all; some of them can be made more robust against accidental data loss through shell settings. In particular:

• On the command line, cp and mv will overwrite any existing target file, but you can make them prompt:

  alias cp='cp -i'
  alias mv='mv -i'
  

  I recommend these two aliases because without them, cp and mv do two jobs: copying/moving and deleting. Not having cp and mv delete files is more in keeping with the unix philosophy (one command does one job) and less error-prone. (This is completely different from rm -i, which asks for confirmation before doing its job — such a systematic prompt tends to trigger an automatic response and thus becomes a useless annoyance.)

• You can make the > redirection operator only accept to create files, so that you have to write >|foo to allow overwriting an existing file foo.

  set -o noclobber
  

There is a FUSE filesystem that automatically keeps copies of old versions: copyfs, available for most unices (*BSD, Linux, OSX, Solaris). Of course, that can use a lot of resources.

If you've moved a file to a different directory and remember (part of) its name but not its location, you can use the locate command to find it.

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The best way to protect against such accidents is to use a version control system (cvs, bazaar, darcs, git, mercurial, subversion, ...). It takes a little time to learn, but it pays off awesomely in the medium and long term.