Bash：使用函数执行带引号的命令

Question

I have a generic function which executes a given command, prints its output to the console and returns the command's output in the same time:

# Command execution
# Executes a given command, redirect stdout to stderr, prints output and returns exit code
# Function arguments:
#   - $1: the command to be executed
cmd_exec() {
    cmd=$1

    exec 5>&2
    echo "Executing command '$cmd' ..."
    output=`"${cmd[@]}" 2>&1 |tee /dev/fd/5; exit ${PIPESTATUS[0]}`
    status=$?
    echo "Command exited with status code: $status"
    echo

    echo "$output"

    echo
    return $status
}

backup_cmd=(sudo -u postgres sh -c '/usr/bin/pg_dump -U postgres -Fc database > /path/to/file')

cmd_exec $backup_cmd
status=$?
if [ "$status" -ne "0" ]; then
    echo "Error during backup!"
fi

When I execute the command I see that only the command sudo is executed and this is because I'm getting the sudo help output:

Executing command 'sudo' ...
Command exited with status code: 1

usage: sudo -h | -K | -k | -V
usage: sudo -v [-AknS] [-g group] [-h host] [-p prompt] [-u user]
usage: sudo -l [-AknS] [-g group] [-h host] [-p prompt] [-U user] [-u user]
            [command]
usage: sudo [-AbEHknPS] [-r role] [-t type] [-C num] [-g group] [-h host] [-p
            prompt] [-T timeout] [-u user] [VAR=value] [-i|-s] [<command>]
usage: sudo -e [-AknS] [-r role] [-t type] [-C num] [-g group] [-h host] [-p
            prompt] [-T timeout] [-u user] file ...

Note: I wrote the cmd_exec generic function because I need to send the output of the command to both stdout and stderr because I want its output to be printed on the console during the execution without waiting the execution to finish.

Answer 1

When you assign this array:

backup_cmd=(sudo -u postgres sh -c '/usr/bin/pg_dump -U postgres -Fc database > /path/to/file')

You don't want to pass it like that to your function:

cmd_exec $backup_cmd

In this case, only the first element of the array will be passed, ie sudo .

You should pass the array elements as double-quoted expansion:

cmd_exec "${backup_cmd[@]}"

There's no need to store parameters to your local variable cmd in your function, you may use the function parameters as $@ instead:

# Command execution
# Executes a given command, redirect stdout to stderr, prints output and returns exit code
# Function arguments:
#   - $@: the command to be executed along with its arguments
cmd_exec() {
    exec 5>&2
    echo "Executing command '$cmd' ..."
    output=`"$@" 2>&1 |tee /dev/fd/5; exit ${PIPESTATUS[0]}`
    status=$?
    echo "Command exited with status code: $status"
    echo

    echo "$output"

    echo
    return $status
}

Please note that variables will not be expanded in single-quoted arguments. In other words, if you want to set the arguments optional like this:

backup_cmd=(sudo -u postgres sh -c '$pgdump -U $username -Fc $database > $filename')

You need to use double quotes instead:

backup_cmd=(sudo -u postgres sh -c "$pgdump -U $username -Fc $database > $filename")