occasional coherence

In our test environment, we automatically install a bunch of utilities — like Notepad++ and the Sysinternals tools — on every Windows system. As part of this, I wanted to add some directories to the Windows system path so these utilities could be easily accessed from the command line. I knew that this could be done manually through the System applet in Control Panel, but it took me a few minutes to figure out how to do it programmatically.

When you edit the system path from the Control Panel, what you’re actually doing is modifying the registry value HKLM\System\CurrentControlSet\Control\Session Manager\Environment\Path. So I wrote a very simple VBS script that takes a directory as an argument and appends it to the value in the registry. Note that the key won’t be re-read until the next time you log into Windows, so your path won’t actually be updated until then.

PathRegKey = "HKLM\System\CurrentControlSet\Control\Session Manager\Environment\Path"
If WScript.Arguments.Count = 0 Then
 WScript.Echo "Please specify a path to add."
 WScript.Quit(1)
End If
Set WshShell = WScript.CreateObject("WScript.Shell")
UpdatedPath = WshShell.RegRead(PathRegKey) & ";" & WScript.Arguments(0)
WshShell.RegWrite PathRegKey, UpdatedPath, "REG_EXPAND_SZ"

On occasion, I’ve wished there was a Linux feature that enabled me to run any command once the next time the system comes up (sort of similar to Windows’ RunOnce). The last time I needed this, I put together a simple init script to provide the functionality. I use this on Debian, but it should work on any UNIX-y OS with Sys-V style init. Create a file called /etc/init.d/runonce with the following content. Don’t forget to make it executable (chmod a+x).

#! /bin/sh
### BEGIN INIT INFO
# Provides: runonce
# Required-Start:
# Required-Stop:
# Should-Start:
# Default-Start: S
# Default-Stop:
# Short-Description: RunOnce
# Description: Runs scripts in /usr/local/etc/runonce.d
### END INIT INFO

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
RUNONCE_D=/usr/local/etc/runonce.d

. /lib/init/vars.sh
. /lib/lsb/init-functions

do_start () {
 mkdir -p $RUNONCE_D/ran > /dev/null 2>&1
 for file in $RUNONCE_D/*
 do
 if [[ ! -f "$file" ]]
 then
 continue
 fi
 "$file"
 mv "$file" "$RUNONCE_D/ran/"
 logger -t runonce -p local3.info "$file"
 done
}

case "$1" in
 start|"")
 do_start
 ;;
 restart|reload|force-reload)
 echo "Error: argument '$1' not supported" >&2
 exit 3
 ;;
 stop)
 # Do nothing
 ;;
 *)
 echo "Usage: runonce [start|stop]" >&2
 exit 3
 ;;
esac

Then, you’ll need to symlink this script into the directories for the appropriate runlevels, which can be done easily on Debian with the following command:

update-rc.d runonce defaults

Finally, create a directory called /usr/local/etc/runonce.d. Now, you can simply put executable scripts or symlinks to utilities on the system into that directory. They’ll be run the next time you boot up, and then moved into the subdirectory /usr/local/etc/runonce.d/ran for posterity.