Shell script continues to run even after exit comm

问题:

My shell script is as shown below:

#!/bin/bash

# Make sure only root can run our script
[ $EUID -ne 0 ] && (echo "This script must be run as root" 1>&2) || (exit 1)

# other script continues here...

When I run above script with non-root user, it prints message "This script..." but it doe not exit there, it continues with the remaining script. What am I doing wrong?

Note: I don't want to use if condition.

回答1:

You're running echo and exit in subshells. The exit call will only leave that subshell, which is a bit pointless.

Try with:

#! /bin/sh
if [ $EUID -ne 0 ] ; then
    echo "This script must be run as root" 1>&2
    exit 1
fi
echo hello

If for some reason you don't want an if condition, just use:

#! /bin/sh
[ $EUID -ne 0 ] && echo "This script must be run as root" 1>&2 && exit 1
echo hello

Note: no () and fixed boolean condition. Warning: if echo fails, that test will also fail to exit. The if version is safer (and more readable, easier to maintain IMO).

回答2:

I think you need && rather than||, since you want to echo and exit (not echo or exit).

In addition (exit 1) will run a sub-shell that exits rather than exiting your current shell.

The following script shows what you need:

#!/bin/bash
[ $1 -ne 0 ] && (echo "This script must be run as root." 1>&2) && exit 1
echo Continuing...

Running this with ./myscript 0 gives you:

Continuing...

while ./myscript 1 gives you:

This script must be run as root.

I believe that's what you were looking for.

回答3:

I would write that as:

(( $EUID != 0 )) && { echo "This script must be run as root" 1>&2; exit 1; }

Using { } for grouping, which executes in the current shell. Note that the spaces around the braces and the ending semi-colon are required.