OPS245 Scripting Exercises dev

What is scripting?

Why write a script?

Scripting is an essential skill for system administrators. A good system administrator (or sysadmin) is a lazy one. They write scripts to automate repetitive tasks such as creating users or backing up files/systems.

Terminal vs script file

A shell script is nothing more than a sequence of shell commands. Any command you put in a shell script can be executed just as well in a terminal. In fact no matter how complex your script is - you can run the entire thing from a terminal window without executing the script. Some of the earliest scripts people learn to create are the commands in the same sequence they would issue them from the command line, only in a script with the appropriate shebang line at the top. You learned about shebang lines in ULI101. The Bash shebang line is #!/bin/bash. The Python 3 shebang line is #!/usr/bin/env python3. The shebang line is the path to the interpreter, and must be the first line of your script.

Runnning a command

• How to run a command in the current directory or another directory or a directory in the $PATH
• That programs you run need to have execute permission
• What your $PWD is, pwd command
• Check the return code from a command by examining $?

Variables

• How to create a variable and set a value in it
• How to get the value from a variable
• Differences in how bash and python handle variables

Getting input from the user

• The read command in bash
• the input() function in python

Quotes

• Why use single or double quotes
• The difference between single and double quotes
• Backquotes

Redirecting output

• How to redirect output from a command to a file
• How to pipe output from one command to another command

Basic commands

• cat
• grep
• cut

Conditional statements

Bash

• if
• test, [

Python

• Python has conditional statements, we just haven't covered them yet.

Exercises

You can do these exercises in any order, and change them in any way you like.

• Create a bash script that will print Hello, then list the contents of the / directory, then print Good Bye.
  • Create a python script that does the same thing.
• Create a bash script that will run your other script twice.
  • Run this new script from different locations, and see if it always works. Fix it if it doesn't.
• Create a bash script to display the contents of /etc/sysconfig/network-scripts/ifcfg-ens33
  • Pipe the output to cat
    • Pipe that output to cat. See if you understand why that doesn't seem to do anything
• Create a bash script which will use cat and grep to find the line with BOOTPROTO in /etc/sysconfig/network-scripts/ifcfg-ens33
  • Modify that script so that it doesn't need cat anymore.
• Create a bash script in which you will create a variable called BP.
  • Assign to that variable the value BOOTPROTO="dhcp" (the equal sign and quotes are part of the value).
  • Use the cut command to retrieve the part between the double-quotes (in this case that's: dhcp).
  • Save the result in a variable, and print that variable.
• Combine the two scripts above into one. The script should tell you what the value of BOOTPROTO from /etc/sysconfig/network-scripts/ifcfg-ens33 is.
• Create a python script that will prompt the user for the name of the interface they want to search (e.g. ens33), then prompt them for the parameter they wish to see.
  • Store the responses from the user in variables and use them to grep the appropriate file for the parameter the user asked for. Display it's current value.
  • Note: As we have not covered conditional statements or loops in python yet, you can assume the user always provides usable responses.
• Use the ls and wc commands to find how many log files there are in /var/log/
  • Add a grep command to find how many of a certain type of log file there are (e.g. vmware-network log files)
• Use the history and grep commands to find any command you ran in the past that contained a certain keyword (like .sh or cat)
• Write a bash script which will use the whoami, hostname, date, and lvs commands to create a report.txt file containing all that information.
  • Set it up so that the date (in YYYY-MM-DD format) is in the filename of the report, e.g. report-YYYY-MM-DD.txt
• Write a bash script that will ask the user for a process name, will check whether that process is running, and if it is: it will print "The process is running". If it isn't: it will print "The process is not running".
  • Modify that script to include the number of processes with that name that are running.
• Write a script that will use a for loop and the cut command to get a list of usernames from the /etc/passwd file and print one username perline.
  • For each user: using an if statement check whether the directory /home/thatusername exists and then each line will look like: "user1: home directory does not exist" or "user2: home directory exists".
  • Instead of checking for /home/thatusername check for the home directory in the passwd file line for that user.