A node program that is also a shell script

Here is the code with a JavaScript syntax highlighter:

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#!/bin/sh
true /* ignored by js

if which node > /dev/null; then
    this_file=$(readlink -f $0)
    exec node $this_file
else
    echo You must install node to run this program
fi

exit 0
ignored by sh
*/

console.log('i am in node');

and with a Shell syntax highlighter:

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#!/bin/sh
true /* ignored by js

if which node > /dev/null; then
    this_file=$(readlink -f $0)
    exec node $this_file
else
    echo You must install node to run this program
fi

exit 0
ignored by sh
*/

console.log('i am in node');

How does it work?

It’s a shell script. Check the first line. #!/bin/sh tells the system to execute this file with /bin/sh.

Near the end, there’s a exit 0 statement. It ends the script shell. /bin/sh won’t read what’s after this line. So it can be JavaScript.

Now, we want this file to be a valid NodeJS file. The first line will be ignored since it’s the shebang. We have to comment the shell code between /* */. A line can’t start with a /* since it’s not a valid shell command. We need some code that works in both language.

true is perfect for that purpose. In shell, it’s just a command that always succeeds and ignores any parameters. In JS, it’s the true keyword.

true /* opens the JS comment block and is valid in both languages. Finally, we can close the block with a simple */ since we do it after the exit 0.

What’s the point?

In the example it’s used to check if node is installed. You could even install it if it’s not there. If it’s installed, it simply executes node with the current file as first parameter.

But mostly, it was fun to write.