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Zoey Hewll
Asked: 2016-05-11 00:10:52 +0800 CST

Strange behaviour using sudo with pipe

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When I use sudo twice in two piped commands, I get the following output:

$ sudo echo 'hello world' | sudo cat
[sudo] password for zoey: [sudo] password for zoey:

And must enter my password twice. The first time, it is hidden as usual, but the second is shown in plaintext.

$ sudo echo 'hello world' | sudo cat
[sudo] password for zoey: [sudo] password for zoey: 
password123456seven
hello world

After the command exits, anything I type to the command line is hidden, as if I were typing a password, although command outputs work (mostly) fine. This behaviour continues until I close the terminal.

I tried:

$ echo 'hello world' | sudo cat
$ sudo echo 'hello world' | cat

And both seem to have normal behaviour.

I don't want to have to use $ sudo bash -c "echo \'hello world\' | cat", which seems overly clunky, and would make quoted text a nightmare to handle.

Also, before anyone asks, yes, I know that echo and cat don't often require root permissions.

sudo

1 Answers

  1. Not sure if this makes you feel better, but what you are observing doesn't occur in Ubuntu 16.04. It does occur in Ubuntu 15.10 (which is what I presume you're using...or perhaps something older?).

    Fortunately, I have a 16.04 and a 15.10 machine to try. Under 16.04, I only have to enter the password once.

    Not sure where the difference is, though. I just checked and both are using the same version of bash (4.3.42). I don't believe there are any settings in my .bash* files that is changing the behaviour...

    (Perhaps you can try an Ubuntu 16.04 boot disk to confirm yourself what I'm seeing?)

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