bash script: sudo no interactive echo redirection to a file

Question

in a bash script I'm trying to redirect a text printed with echo with sudo non interactive to a file. But I'm not clear about how to do it.

I tried with this code:

echo $sudopass| sudo -S echo "user ALL=(ALL) NOPASSWD:ALL" >     /etc/sudoers.d/ansible

Answer 1

Output redirection is not affected by elevated sudo permissions. The part that you sudo is the echo , not the redirection of that command's output.

That will still happen with your current user's permission.

So you need a way to append a line to a file that does not involve output redirection.

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Note: Earlier version of this answer showcasing sed removed as sed balks if the target file is empty or non-existing. As I wanted to keep the gist of the answer intact -- "how to avoid output redirection" -- I added instructions on how to use vi for the same purpose.

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Every POSIX-compliant system needs to have the vi / ex editor. (On contemporary Linux machines usually a link starting Vim in compatiblity mode.) You can "remote-control" ex / vi / Vim through the command line:

vi -es -c "normal! G" -c "normal! ouser ALL=(ALL) NOPASSWD:ALL" -c "x" /etc/sudoers.d/ansible

(This is without the sudo part for clarity.)

Explanation:

• -e starts vi in "ex mode". (Equivalent to calling ex .)
• -s means "silent" -- no prompts, no messages.
• -c passes a command to the editor to be executed once the first file has been read.
• "normal! G" first puts the editor in "normal mode" -- that is what you would find yourself in if you started vi interactively; ex is in "command mode" by default (as if you entered : in vi). The G moves the cursor to the last line.
• "normal! o..." again activates normal mode, adds a line after the current line, and activates "insert mode". The rest of the string is entered verbatim.
• "x" saves the file and exits the editor.

The command line including the sudo part:

echo $sudopass | sudo -S vi -es -c "normal! G" -c "normal! ouser ALL=(ALL) NOPASSWD:ALL" -c "x" /etc/sudoers.d/ansible