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Sigurd Alnæs
Asked: 2024-09-04 02:48:11 +0800 CST

heredoc not working in Ubuntu 24.04

  • 772

Upgraded to 24.04 on two servers, and cannot run remote script (heredoc) on second server from first server as I did on 22.04 before. Is this option removed from Ubuntu 24.04?

server

1 Answers

  1. Best Answer

    I'm assuming your indentation is some version of this

    #!/bin/bash
function getversion() {
    if  backdock="$(cat <<EOF
            who
            if vers=$( cat ~/version.txt )
            then
                echo "$vers"
                exit 0
            else
                exit 1
            fi
            logname
EOF
        )"
        ssh -t [email protected] "$backdock"
    then
        return
    else
        false
    fi
}
getversion

    It's not right to say "the heredoc is executed on 192.168.1.2", the heredoc is processed on your local machine including the command and variable substitutions. The resulting text is passed as an argument to ssh to be executed on the remote host.

    If you want that to be literal text, then quote the heredoc marker:

    cat <<'EOF'
# ....^...^
# the rest stays the same

    Note you are using a form of the anti-pattern

    if (expression)
  return true
else
  return false
end

# expression is already a boolean, just return it
return expression

    ssh already exits with a success/failure status, and a function exits the status of the last command executed:

    function getversion() {
    backdock="$(cat <<'EOF'
            who
            if vers=$( cat ~/version.txt )
            then
                echo "$vers"
                exit 0
            else
                exit 1
            fi
            logname
EOF
    )"
    ssh -t [email protected] "$backdock"
}

    Other notes:

    • We don't even really need a heredoc, plain quoting works as well

      function getversion() {
    ssh -t [email protected] '
            who
            if vers=$( cat ~/version.txt )
            then
                echo "$vers"
                exit 0
            else
                exit 1
            fi
            logname
    '
}

    • logname is never executed, one of the exits happens first (it could be I didn't understand your indentation)

    • capturing the version file is awkward, relying on cat failing. How about

      if [[ -f ~/version.txt ]]; then
    cat ~/version.txt
else
    exit 1
fi
    • 0