Scripting basics: automate the boring stuff

You don’t need to be a programmer to work in IT, but a little scripting changes your career. Anything you do more than twice by clicking can probably be done in seconds with a script, and done the same way every time.

What a script is

A script is just a text file full of the same commands you’d type at the command line (step 2), run in order. Instead of typing ten commands, you run one file.

• PowerShell is the scripting language for Windows and Microsoft services. Windows includes Windows PowerShell 5.1, and the newer, cross-platform PowerShell 7 is a free download.
• Bash is the standard on Linux, and works on macOS too.

If you’ll mostly support Windows offices, start with PowerShell.

PowerShell in five minutes

PowerShell commands follow a Verb-Noun pattern, which makes them easy to guess:

Get-Process        # list running programs
Get-Service        # list services
Stop-Process -Name notepad
Restart-Service -Name Spooler   # restart the print spooler

The real power is the pipeline (|), which passes results from one command into the next:

# The 5 programs using the most memory
Get-Process | Sort-Object WorkingSet -Descending | Select-Object -First 5 Name, WorkingSet

Variables hold values, and loops repeat things:

$computers = 'PC1', 'PC2', 'PC3'
foreach ($pc in $computers) {
    Test-Connection -ComputerName $pc -Count 1 -Quiet
}

Your first useful script

Here’s a small script that checks free disk space and warns you when a drive is getting full, a classic cause of mysterious problems:

# Warn about any drive with less than 15% free space
Get-CimInstance Win32_LogicalDisk -Filter "DriveType=3" | ForEach-Object {
    $freePercent = [math]::Round(($_.FreeSpace / $_.Size) * 100, 1)
    if ($freePercent -lt 15) {
        Write-Warning "$($_.DeviceID) has only $freePercent% free"
    } else {
        "$($_.DeviceID) is fine ($freePercent% free)"
    }
}

Save it as check-disk.ps1, then run it from PowerShell with .\check-disk.ps1. If Windows blocks it, the setting that controls this is called the execution policy; Set-ExecutionPolicy RemoteSigned -Scope CurrentUser allows your own scripts to run.

Bash in two minutes

The same idea on Linux:

#!/bin/bash
# Warn about any filesystem over 85% full
df -h --output=pcent,target | tail -n +2 | while read pct mount; do
  if [ "${pct%\%}" -gt 85 ]; then
    echo "WARNING: $mount is $pct full"
  fi
done

Save it as check-disk.sh, make it runnable with chmod +x check-disk.sh, and run it with ./check-disk.sh.

Habits that keep scripts safe

• Test in your home lab first (step 7), never on a live system.
• Read before you run. Never paste a script from the internet without understanding what each line does, especially anything with “delete,” “remove” or “format” in it.
• Start read-only. Scripts that only look at things (Get commands) can’t break anything. Add changes once you trust the output.
• Use -WhatIf in PowerShell. Many commands support it, and it shows what would happen without doing it.
• Comment your scripts (lines starting with #), so you’ll understand them in six months.

Where to go next

• Get-Help and Get-Command are built in and excellent: Get-Help Get-Service -Examples
• Pick one task you do repeatedly and script it. Real problems teach faster than tutorials.
• There’s a collection of read-only Active Directory commands here for once you’ve built the domain from step 7.

Key takeaways

• A script is just commands in a file, run in order.
• PowerShell for Windows, bash for Linux.
• The pipeline is what makes PowerShell powerful.
• Test in a lab, read before you run, and start read-only.