[POWERSHELL] Logged On Users v1.0

# Purpose:        Stamps usernames to a file as users log on, then removes them when they log off.
#                 Clears this file at each boot/reboot. Purpose is to keep a comma-separated file
#                 listing all users logged on to the system so we can query it with other text-based tools.
# Requirements:   1. Write-access to the log location
# Author:         vocatus on reddit.com/r/sysadmin and /r/usefulscripts
# History:        1.0   Initial write

# Usage:          Call the script with one of the following flags:
#                   -logon    Add username to the list of current users
#                   -logoff   Remove username from the list of current users
#                   -flush    Flush all usernames (use when rebooting/booting)


########
# Prep #
########
$VERSION="1.0"
$UPDATED="2014-01-21"
$CUR_DATE=get-date -f "yyyy-MM-dd"

#############
# VARIABLES # -- Set these to your desired values
#############
# Rules for variables:
#  * Quotes are required              (e.g.:  "c:\directory\path"        )
#  * NO trailing slashes on paths!    (bad:   "c:\directory\"            )
#  * Spaces are okay                  (okay:  "c:\my folder\with spaces" )
#  * Network paths are okay           (okay:  "\\server\share name"      )
#                                     (       "\\172.16.1.5\share name"  )

# Where to keep the file containing the list of logged-on users? Regular users must have write-access to this location
$LOGPATH=$env:systemdrive + "\Logs"
$LOGFILE="logged_on_users"


#############
# EXECUTION #
#############
# If no argument passed, spit out an error and die
if (! $args) {
    write-host ""
        write-host "ERROR: No action specified" -f red
        write-host ""
        write-host "Actions are: "
        write-host "  -logon   Stamp username to" $LOGPATH\$LOGFILE -f gray
        write-host "  -logoff  Remove username from" $LOGPATH\$LOGFILE -f gray
        write-host "  -flush   Flush all usernames from" $LOGPATH\$LOGFILE -f gray
        write-host ""
        write-host "  e.g. .\logged_on_users.ps1 -logon" -f gray
        write-host ""
        break
}

# Add this user to the list of current users
# Direct call to .net framework since PowerShell doesn't have an easy way to write to a file without a new-line
if ($args -eq "-logon") {
    [System.IO.File]::AppendAllText("$LOGPATH\$LOGFILE", $env:username + ",")
}

# Remove user from list of current users
if ($args -eq "-logoff") {

    # Do a find-replace on our username and remove it from the file
    (gc "$LOGPATH\$LOGFILE" -raw) | Foreach-Object {$_ -replace ($env:username+","), ""} | sc $LOGPATH\$LOGFILE -force

    # This is a workaround to using "set-content" since SC automatically inserts CR;LF (carriage return; line feed) which we don't want
    # Basically read the file into a variable ("thing"), then crawl it and remove new line characters
    $thing = Select-String -Pattern "\w" -Path $LOGPATH\$LOGFILE | foreach {$_.line}
    # Now use the .net IO.file function to write it back out, WITHOUT inserting a CR;LF
    [System.IO.file]::WriteAllText("$LOGPATH\$LOGFILE",$thing)
}

# Flush the log file ("clear-content" aka clc)
if ($args -eq "-flush") {
    clc $LOGPATH\$LOGFILE
}