I typed it by mistake but bash didn't print any errors (but created an empty file) so I thought maybe it actually means something ? (e.g. date |> tmp.txt)

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    Are you sure the command isn’t of the form date |> tmp.txt cmd2? Because that changes the answer. – Konrad Rudolph Sep 25 '18 at 13:26

That seems to be just a pipeline where the second part is an empty command, only containing the redirection. Writing it as date | >file might make it easier to interpret. The empty command doesn't do anything but process the redirection, creating the file.

date >| file on the other hand would act as an override for the noclobber shell option, which prevents the regular > from overwriting existing files.

$ touch foo; set -o noclobber
$ date > foo
bash: foo: cannot overwrite existing file
$ date >| foo       # works

Yes, it will not throw error because for bash > file means redirect to a file named file. As in your case there is nothing to redirect to file, bash will just create a file name file with nothing in it.

[bd@centos-6.5 my-tests]$ date | > my_file
[bd@centos-6.5 my-tests]$ cat my_file
[bd@centos-6.5 my-tests]$ 
  • Funny. Zsh has a different behavior: after the command, my_file contains the output of date. – N.I. Sep 25 '18 at 9:28
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    @NajibIdrissi, in zsh, when there are only redirections and no command, zsh runs the $NULLCMD command (cat by default) or $READNULLCMD (a pager by default) if there are only input redirections. – Stéphane Chazelas Sep 25 '18 at 9:34

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