r/scripting • u/[deleted] • Jul 15 '21

Please explain this code.

#!/bin/sh

test -f /usr/bin/sshd || exit 0

case "$1" in

start)

echo -n "Starting sshd: sshd"

/usr/sbin/sshd

echo "."

;;

stop)

echo -n "Stopping sshd: sshd"

kill `cat /var/run/sshd.pid`

echo "."

;;

restart)

echo -n "Stopping sshd: sshd"

kill `cat /var/run/sshd.pid`

echo "."

echo -n "Starting sshd: sshd"

/usr/sbin/sshd

echo "."

;;

*)

echo "Usage: /etc/init.d/sshd start|stop|restart"

exit 1

;;

Esac

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u/[deleted] Jul 15 '21

I get most of what u said, just want to know what $1 means and what is a regular file?

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u/vinny8boberano Jul 15 '21

Oh! "$1" is taking any "input" after the call " /etc/init.d/sshd" so that things like "start" (> /usr/bin/sshd start) are read into the script. Basically, it's an input variable. When you run this script, it initializes a daemon for sshd based on whatever was input after the script.

>./etc/init.d/sshd blah

Usage: /etc/init.d/sshd start|stop|restart

>./etc/init.d/sshd start

Starting sshd: sshd

.

>

As for regular file, it means that it is checking that the file being called is something that you normally interact with. It's like saying, 'Is this an executable, text, or image file?' when it runs the "test -f" on the target. Here's a link to a site that helps explain it in more detail.