Commit 93ecccc

As \*nix systems remain the top choice in servers and networking, understanding their **shell** has remained an important factor for IT, IS, and Networking professionals. Even for Windows systems (MS Servers) the *ability to automate tasks with Powershell* is considered an essiential skill. This article, part of an Intro to Networking class, we will overview the shell scripting commands most used in Powershell and bash (standard Linux Shell) - full coverage is provided in the "Scripting" course.

- in the shell's language

- executables built-in to the kernel

- other programming languages (Python, C#, Perl)

tidy -xml -iq test.xml

On Linux you can get more infomation using ***\<command \-\-help\>*** and in Powershell using ***Get-Help \<command\>***. The basic shell scripting commands are:

#bash

echo "Hello World"

Write-Host "$test World"

Write-Host

# This is the same in bash/Powershell (aliased to Get-Content)

cat filename.txt

Frequently, used with pipes to pass contents of file between cmdlets/executables or as quick check of file.

Grep (and egrep) can have their own class. Select-String is Powershell's "equiv" but its not quite equal. As a basic intro: it searches files for a provided string or pattern (Regex).

#Search for any instance of "test in txt files"

For more see [Digital Ocean's guide of Grep](https://www.digitalocean.com/community/tutorials/using-grep-regular-expressions-to-search-for-text-patterns-in-linux).

This command is the same in PowerShell or \*nix. It lists the folders and files present in a particular directory (either current or provided path). Powershell's **ls** is actually `ls -l` (long list: i.e. include details) in \*nix.

So these are ran together often enough. cd changes your directory (**. = current directory, .. = parent directory**) and pwd prints it out. Again, these are the same in both Linux and Powershell and would look like:

# Assuming in /Users

cd Users/Sam #change to this directory/sub-directory

pwd # would print /Users/Sam

Same on both again: makes a directory with default permissions (and current user as owner).

cd /home

mkdir Sam

cd Sam

pwd # would print /home/Sam

As we are using a command-line: copy, move, and rename are a bit different. Copy is essentially the same (it makes a copy of the original file). However, move (think cut) deletes the original and makes a new copy of the file whereas rename just changes the file name. So many times you'll use ***mv*** over ***rename*** because you just want to recreate the file (you use rename to keep permissions and owner the same).

# both systems

No real powershell equivilent (can use *-RunAs* flag but its not the same).

Tuning and debuging of network....add IP

Can be used to display:

- routing tables

- network connections

- masquerade connections

- interface statistics

- even more

Queries DNS and fetches information (ip address).

Whenever server is left unattended this can be queried (ran) to determine if any downtime happened. Easy to automate by just redirecting (see below) to a log which is periodically checked.

When it comes to automation, the ability to redirect output (pipe it) is essential. There are several variants on piping but it can be considered as the *couts, System.out, or other file operations* dealt with in most programming languages. The following are the main **pipes**.

`>` is used to **redirect output** and ***write*** *it to a file*.

`>>` is used to **redirect output** and ***append*** *it to the end of a file*.

In Powershell, you cannot redirect pure strings (literally `Write-Output or "Hello World"`). See Piping for how to perform this.

So this is the scripting equivilent of *chaining*, that fun task where we passed information from one command to another (like a builder class: ```Build b = Build.create().withParameterA("A").withParameterB(2);```). In fact, with Powershell its the only way to redirect direct strings to files without having to deal with Array conversions using two cmdlets:

`Set-Content` is used to **redirect output** and ***write*** *it to a file*.

# -i = ignore case, -o = only words; xargs = make array into arguments

# ./ = path to script (assumes shebang and executable permissions set)

grep -io "john .*" ./*.txt | xargs ./parse_users.py