Using bash process substitution for a sudo command

Question

I would like to use bash process substitution for a sudo command.

For example, here\'s a non-sudo command that works for me:

$ cat <(echo \"installed.         


        

Answer 1

sudo bash  -c 'cat <(echo "installed.txt")'

Answer 2

The behaviour described in the question is due to the design of sudo.

$ sudo cat <(echo "installed.txt")
cat: /dev/fd/63: Bad file descriptor

The error occurs because sudo has a default behaviour which closes file descriptors except for standard input, output and error. As described on the man page:

By default, sudo will close all open file descriptors other than standard input, standard output and standard error when executing a command.

This behaviour can be overridden with the -C (or --close-from) option to specify a file descriptor number below which files should not be closed. However, use of this option must be permitted by an administrator: the following needs to be added to /etc/sudoers

 Defaults closefrom_override

With that in place, the command will work if -C is used:

$ sudo -C64 cat <(echo "installed.txt")
installed.txt

(here the number 64 was given because it was greater than the 63 in the error message).

Answer 3

The best approach is probably to put everything in a script, and run that script with sudo.

Answer 4

Try doing this in your shell :

$ sudo bash -c 'cat <(echo "installed.txt for UID=$UID")'
installed.txt for UID=0