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To use a command with the "echo into a file" redirection operator >> through sudo... command, I have written that to redirect through standard input to the sudo process, executed as the superuser. The command to redirect was echo "tun" >> /etc/modules-load.d/tun.conf, here I put whoami in its place.

I tried

echo 'whoami' | sudo -i '$SHELL -c "exec $(< /dev/stdin)"'

and next,

echo 'whoami' | sudo -i '$SHELL -c "$(< /dev/stdin)"'

and sh responded -sh: /bin/sh -c "$(< /dev/stdin)": not found.

What is that for? Why does the Alpine Linux distribution shell not find my commands executed through sudo?

sudo -V (version number and compiled versions):

Sudo version 1.9.15p5
Sudoers policy plugin version 1.9.15p5
Sudoers file grammar version 50
Sudoers I/O plugin version 1.9.15p5
Sudoers audit plugin version 1.9.15p5

Thank you for anything answered! 🙂

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  • echo 'whoami' | sudo -i $SHELL -c "exec $(< /dev/stdin)" Commented Nov 11, 2024 at 19:59
  • @ArkadiuszDrabczyk I think you need exec $(< /dev/stdin) in two ', sorry. Commented Nov 11, 2024 at 20:34
  • why? Have you run it? Commented Nov 11, 2024 at 21:47

1 Answer 1

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Note that the error message says that the file /bin/sh -c "$(< /dev/stdin)" is not found. It tries to execute that whole string as a command because you told sudo to do so (the string was the only argument to the command, apart from the unnecessary -i option).

Instead, you'd want to use

echo whoami | sudo "$SHELL" -c 'exec $(< /dev/stdin)'

... which runs $SHELL with -c and exec $(< /dev/stdin) as arguments. Note, though, that if $SHELL is a shell that does not understand process substitutions, such as sh, you would not expect the in-line shell script to produce any output. Instead, use $SHELL -s (run the shell and get it to read its commands from standard input):

$ echo whoami | sudo "$SHELL" -s
root
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  • Thank you! Why can't the whole string with "exec $" be executed? Commented Nov 11, 2024 at 20:16
  • @EdwardJ Because there is no such command. It's the difference between ls -l and "ls -l" (try it). One is a command with an option, the other a command that does not exist. Commented Nov 11, 2024 at 20:24
  • OK, the answer works. Commented Nov 11, 2024 at 20:27

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