Skip to main content

​
Command Line Interfaces

The command line is one of the most powerful tools for system administrators. While graphical interfaces make many tasks easier, the command line provides:
  • More direct system communication
  • Better automation capabilities
  • Access to all system features
  • Scriptability for repetitive tasks

​
PowerShell (Windows)

PowerShell has become the default interpreter in Windows 10 (since November 2017), replacing CMD as the primary administrative tool.

​
Why PowerShell?

Object-Oriented

Everything is an object, not text strings, providing richer data manipulation

.NET Integration

Full access to .NET Framework capabilities

Cross-Platform

PowerShell Core runs on Windows, Linux, and macOS

Consistent Syntax

Verb-Noun naming convention makes commands predictable

​
cmdlet Structure

All PowerShell cmdlets follow the Verb-Noun pattern: 
Get-Process      # Get information
Set-ExecutionPolicy  # Set configuration
New-Item         # Create new item
Remove-Item      # Delete item

​
Common Verbs

VerbPurposeExample
GetRetrieve dataGet-Process
SetModify settingsSet-Location
NewCreate objectsNew-Item
RemoveDelete objectsRemove-Item
EnableActivate featureEnable-WindowsFeature
DisableDeactivate featureDisable-FirewallRule
InstallInstall softwareInstall-Module
UninstallRemove softwareUninstall-Package
TestVerify conditionTest-Path
MoveRelocate objectMove-Item

​
Parameters

Parameters modify command behavior: 
Get-ChildItem -Path C:\ -Recurse -Force
Get-Process -Name "chrome" | Stop-Process

​
Pipelines

PowerShell’s pipelines pass entire objects between commands: 
# Get processes, sort by ID, select first 5
Get-Process | Sort-Object -Property Id -Descending | Select-Object -First 5

# Get services, filter running ones, export to CSV
Get-Service | Where-Object {$_.Status -eq "Running"} | Export-Csv services.csv

​
Script Files (.ps1)

PowerShell scripts use the .ps1 extension: 
#!/usr/bin/env pwsh
# My first PowerShell script

Write-Host "System Information"
Get-ComputerInfo | Select-Object CsName, OsVersion

​
Help System

PowerShell includes comprehensive help: 
Get-Help Get-Process

​
Execution Policy

PowerShell’s execution policy controls script execution: 
# View current policy
Get-ExecutionPolicy

# Set unrestricted (for development)
Set-ExecutionPolicy -ExecutionPolicy Unrestricted

# Set to remote signed (production)
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned
Changing execution policy requires administrator privileges. Run PowerShell as administrator.
Execution Policy Levels:
PolicyDescription
RestrictedNo scripts can run (default)
AllSignedOnly signed scripts can run
RemoteSignedLocal scripts run unsigned; downloaded scripts must be signed
UnrestrictedAll scripts can run (prompts for downloaded scripts)
BypassNo restrictions, no warnings

​
BASH Shell (GNU/Linux)

BASH (Bourne Again SHell) is the default shell on most Linux distributions.

​
The Prompt

The prompt provides information about your session: 
violin@xubuntu:~$
  • violin - username
  • xubuntu - hostname
  • ~ - current directory (home)
  • $ - regular user (# for root)
Root prompt: 
root@xubuntu:~#

​
Key Features

Press TAB to auto-complete:
  • Commands
  • File names
  • Directory names
  • Variables
Press TAB twice to see all possibilities:
cd /us<TAB><TAB>
# Shows: /usr/ /usr/bin/ /usr/lib/ ...
Navigate command history with arrow keys:
  • ↑ - Previous command
  • ↓ - Next command
  • history - Show command history
  • !123 - Execute command #123 from history
  • !! - Execute previous command
  • !$ - Last argument of previous command
History is stored in ~/.bash_history (default 1000 commands)
Create command shortcuts:
alias ll='ls -lah'
alias update='sudo apt update && sudo apt upgrade'
alias ..='cd ..'
Make permanent by adding to ~/.bashrc
Define reusable functions:
mkcd() {
    mkdir -p "$1" && cd "$1"
}

backup() {
    cp "$1" "$1.backup.$(date +%Y%m%d)"
}

​
Script Structure

BASH scripts follow a standard structure: 
#!/bin/bash
# Script description
# Author: Your Name
# Date: 2024-03-06

# Variables
VARIABLE="value"

# Main code
echo "Script starting..."

# Functions
function my_function() {
    echo "Function called"
}

# Execution
my_function

# Exit with success
exit 0

​
Shebang Line

The shebang (#!) specifies the interpreter: 
#!/bin/bash          # Use bash
#!/bin/sh            # Use sh (POSIX)
#!/usr/bin/env bash  # Use bash from PATH
#!/usr/bin/env python3  # Python script
Using #!/usr/bin/env bash is more portable as it finds bash in the PATH.

​
Making Scripts Executable

# Create script
echo '#!/bin/bash' > script.sh
echo 'echo "Hello World"' >> script.sh

# Make executable
chmod +x script.sh

# Run script
./script.sh

​
Common BASH Constructs

#!/bin/bash

if [ -f "/etc/passwd" ]; then
    echo "File exists"
else
    echo "File not found"
fi

​
Comparing PowerShell and BASH

TaskPowerShellBASH
List filesGet-ChildItemls
Change directorySet-Locationcd
Copy fileCopy-Itemcp
Move fileMove-Itemmv
Delete fileRemove-Itemrm
Create directoryNew-Item -Type Directorymkdir
Display textWrite-Hostecho
View fileGet-Contentcat
Find textSelect-Stringgrep
Sort outputSort-Objectsort
Filter outputWhere-Objectgrep
Both shells support aliases. PowerShell includes aliases that match common BASH commands (ls, cd, cat, etc.).

​
Best Practices

1

Document Your Scripts

Include comments explaining what the script does, author, and date
2

Use Meaningful Names

Variables and functions should have descriptive names
3

Check for Errors

Always verify commands succeeded before continuing
4

Test Before Production

Test scripts thoroughly in a development environment
5

Use Version Control

Store scripts in git for history and collaboration

Build docs developers (and LLMs) love

Get started for freeTalk to us