Shell Scripting

After going through the Bash and Powershell Course, here is a summary of what I was able to learn and demonstrated. For a more detailed summary of my work, follow the link here.

Linux Shells

• A shell is an environment in which we run our commands, programs, and shell scripts. It gathers input from you and executes programs based on that input. When a program finishes, it displays the program's output.

Types of shells

• Bourne shell (sh)
• Korn shell (ksh)
• Bourne again shell (bash)
• POSIX shell (sh)
• C shell (csh)
• TENEX/TOPS C shell (tcsh)

Shell Scripts

The basic concept of a shell script is a list of commands, which are listed in the order of execution.

.The shebang

#!/bin/sh

• This tells the system that the commands that follow are to be executed by the Bourne shell. It's called a shebang because the # symbol is called a hash and ! symbol is called a bang.

Windows PowerShell

Resources:

PowerShell Top Ten Commands

1. Get-content: Get the content of the given item at the specified location.

Get-Content hosts.txt

• You can assign the output to variable

$hosts = Get-Content hosts.txt

2. ForEach-Object: Performs operation against each item in a collection of input objects.

$hosts = Get-Content -Path hosts.txt


$hosts | ForEach-Object {

    $_

}

• $_: represents each host object and will be output on the screen one at time.

$hosts = Get-Content -Path hosts.txt


$hosts | ForEach-Object {

    Write-Host "Hostname: $($_)" -BackgroundColor white -Foregroundcolor black

}

3. Out-File: Sends output to a file.

"My name is Patrick" | Out-File test.txt -Append

"My name is Cmd" | Out-File test.txt -Append

• Writing contents of hosts variable to a file

$hosts = Get-Content -Path hosts.txt


$hosts | ForEach-Object {

    "Hostname: $($_)" | Out-File outputhosts.txt -Append

}

4. Test-NetConnection: Displays diagnostic information for a connection.

$hosts = Get-Content -Path hosts.txt


$hosts | ForEach-Object {

    Write-Host "Testing Host: $($_)"

    Test-NetConnection -ComputerName $_ -port 443

    Test-NetConnection -ComputerName $_ -port 80

    Write-Host ""

}

5. ConvertTo-Json: Converts an object to a JSON-formatted string.

$hosts = Get-Content -Path hosts.txt


$hosts | Convertto-json

$hosts = Get-Content -Path hosts.txt


$hosts[0] | ConvertTo-Json

6. Get-Date: Gets the current date and time.

**For example logging tests to a file with time stamp

$hosts = Get-Content -Path hosts.txt


$hosts | ForEach-Object {

    Write-Host "Testing Host: $($_)" 

    "$(Get-Date): Testing Host: $($_)" | Out-File host_test.log -Append

    Write-Host ""

}

7. Start-Sleep: Suspends the activity in a script or session for the specified period of time.

$hosts = Get-Content -Path hosts.txt


$hosts | ForEach-Object {

    Write-Host "Sleeping for 2 seconds..." -BackgroundColor Black -Foregroundcolor Cyan

    Start-Sleep -Seconds 2

    Write-Host "Testing Host: $($_)" 

    "$(Get-Date): Testing Host: $($_)" | Out-File host_test.log -Append

    Test-NetConnection -ComputerName $_ -port 443

    Test-NetConnection -ComputerName $_ -port 80

    Write-Host ""

}

8. Write-Host: Writes customized output to a host.

$hosts = Get-Content -Path hosts.txt


$hosts | ForEach-Object {

    Write-Host "Sleeping for 2 seconds..." -BackgroundColor Black -Foregroundcolor Cyan

    Start-Sleep -Seconds 2

    Write-Host "Hostname: $($_)" -BackgroundColor white -Foregroundcolor black

    Write-Host ""

}

9. Get-Command: Gets all commands.

Get-Command

• Shows all the powershell commands with the word write in it.

Get-Command **write**

10. Get-Help: Displays information about PowerShell commands and concepts.

• Get help on the Get-Content command online

Get-Help Get-Content -online