Unable to accept user input in bash

Question

while
   echo "Do you want to continue y/n?"
   read install_to_default
   [[ -z $install_to_default || $install_to_default != [yYnN] ]]
do echo "The response is invalid. A valid response is y or n."; done

Running the above script as root causes no problems, but when I try to run the script as a different user with the below changes it causes an infinite loop.

sudo -u piggy -i <<'EOF'
while
    echo "Do you want to continue y/n?"
    read install_to_default
    [[ -z $install_to_default || $install_to_default != [yYnN] ]]
    do echo "The response is invalid. A valid response is y or n."; done
EOF

tshiono · Accepted Answer · 2021-05-21 09:08:14Z

2

The stdin of the sudo process has been redirected to the here-document << and the read command in the loop doesn't wait for the user's input on console. Please try to change the read line to:

read -u 1 install_to_default

Technically it may not be the best idea to use descriptor 1 for the purpose. Strictly we should use other descriptor such as 3 with the -C 4 option to the sudo command. But this solution will require to change the sudoers policy which may rather cause more problems.

answered May 21, 2021 at 9:08

tshiono

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2 Comments

AAB Over a year ago

the bash script will be executed as root, so will it still need a policy change?

tshiono Over a year ago

As for the root privilege, you do not have to change the policy as long as the specified user belongs to the sudoers group.

Léa Gris · Accepted Answer · 2021-05-21 08:53:02Z

1

You cannot read user input this way because the input stream is already captured by the here-document script.

If you want to read user input from the terminal, while using a here-document as the sudo script, then read from /dev/tty

sudo -u piggy -i <<'EOF'
while
    printf %s\\n "Do you want to continue y/n?"
    read -r install_to_default </dev/tty
    [ -z "$install_to_default" ] || [ -n "${install_to_default%[yYnN]}" ]
    do
      printf %s\\n "The response is invalid. A valid response is y or n."
    done
EOF

answered May 21, 2021 at 8:53

Léa Gris

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