Lab 14 mnjk - Revision history

KreidKolo: /* Introduction */

2021-02-19T01:05:06Z

Introduction

← Older revision		Revision as of 01:05, 19 February 2021
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	=Introduction=		=Introduction=
	In this lab you will create and modify some basic python shell scripts. '''You will have to run some of these scripts as SUDO for them to work. If something doesn't work try running as SUDO.'''		In this lab you will create and modify some basic python shell scripts.<br>
			''NOTE: You will have to run some of these scripts as '''SUDO''' for them to work. If something doesn't work try running as '''SUDO'''.''

	=Lab Procedure=		=Lab Procedure=

KreidKolo: /* Introduction */

2021-02-19T00:44:03Z

Introduction

← Older revision		Revision as of 00:44, 19 February 2021
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	=Introduction=		=Introduction=
	In this lab you will create and modify some basic python shell scripts.		In this lab you will create and modify some basic python shell scripts. '''You will have to run some of these scripts as SUDO for them to work. If something doesn't work try running as SUDO.'''

	=Lab Procedure=		=Lab Procedure=
	== Prerequisites ==		== Prerequisites ==

KreidKolo: /* Functions and Experimenting */

2021-02-16T00:58:41Z

Functions and Experimenting

← Older revision		Revision as of 00:58, 16 February 2021
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	<ol>		<ol>
	<li> Just as in BASH we can create functions in python as well. Try entering this simple sample as ''hello-func.py'':		<li> Just as in BASH we can create functions in python as well. Try entering this simple sample as ''hello-func.py'':
	<pre>		<pre>#!/usr/bin/env python3
	#!/usr/bin/~~python~~
	def helloname():		def helloname():
	name = ~~raw_input~~("Enter your name, followed by enter: ")		name = input("Enter your name, followed by enter: ")
	print "Hello "+name+"!"		print("Hello " + name + "!")
	print "This program will welcome you twice to be extra nice!"

			print("This program will welcome you twice to be extra nice!")
	helloname()		helloname()
	print "At this point we could be doing lots of other stuff in our script or be in a loop, etc."		print("At this point we could be doing lots of other stuff in our script or be in a loop, etc.")
	helloname()		helloname()
	print "Thanks for playing!"		print("Thanks for playing!")
	</pre>		</pre>
	This should work pretty much the same way that the BASH equivalent script did. See if you can figure out what will happen when you run it, then try it out and see if you were correct. Note that functions need to be declared (listed) before you use them in your script so it would be common to see them at the beginning of the file as in this example. One difference with functions in Python is how you pass information in and out of functions. Instead of using arguments you include the information in the function call itself and you can return information from the function which can be used immediately or can be stored into a variable. Try modifying ''hello-func.py'' like this:		This should work pretty much the same way that the BASH equivalent script did. See if you can figure out what will happen when you run it, then try it out and see if you were correct. Note that functions need to be declared (listed) before you use them in your script so it would be common to see them at the beginning of the file as in this example. One difference with functions in Python is how you pass information in and out of functions. Instead of using arguments you include the information in the function call itself and you can return information from the function which can be used immediately or can be stored into a variable. Try modifying ''hello-func.py'' like this:
	<pre>		<pre>#!/usr/bin/env python3
	#!/usr/bin/~~python~~
	def askname():		def askname():
	yourname = ~~raw_input~~("Enter your name, followed by enter: ")		yourname = input("Enter your name, followed by enter: ")
	return yourname		return yourname


	def helloname(thename):		def helloname(thename):
	print "Hello "+thename+"!"		print("Hello " + thename + "!")
	print "There are lots of ways to make use of the two functions in this script. We can pass a pre-specified string to a function:"

			print("There are lots of ways to make use of the two functions in this script. We can pass a pre-specified string to a function:")
	helloname("world")		helloname("world")
	print "We can ask for your name and use it immediately as input into the hello function:"		print("We can ask for your name and use it immediately as input into the hello function:")
	helloname(askname())		helloname(askname())
	print "We can take a string already stored in a variable and pass the variable to a function:"		print("We can take a string already stored in a variable and pass the variable to a function:")
	somevariable="Linux Lover"		somevariable = "Linux Lover"
	helloname(somevariable)		helloname(somevariable)
	print "Or we can ask you your name again and store your name in a variable once and then use it a few times:"		print("Or we can ask you your name again and store your name in a variable once and then use it a few times:")
	userentry = askname()		userentry = askname()
	helloname(userentry)		helloname(userentry)
	print "Thanks for playing "+userentry+"!"		print("Thanks for playing " + userentry + "!")</pre>
	</pre>
	See if you can figure out what this script will do and how it works before running it, then try it out and see if you were correct.		See if you can figure out what this script will do and how it works before running it, then try it out and see if you were correct.
	</li>		</li>

KreidKolo: /* Using Loops and Reading User Input */

2021-02-16T00:37:26Z

Using Loops and Reading User Input

← Older revision		Revision as of 00:37, 16 February 2021
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	There are a couple of differences to note when comparing this with the similar BASH script we created. First, instead of using a separate program, like the BASH '''read''' program, we are obtaining user input with the ''input()'' function. This program is then storing the user's input into a certain variable. By default the ''input()'' function saves information as a STRING which is a type of variable which can hold letters and numbers but can't be used for numeric operations like adding, subtracting, looping, etc. Because of this we use the ''int()'' and ''str()'' funtions to switch the data back and forth from the string type to the integer numeric type as needed in various parts of the script. Second, the for statement is using the built-in ''range()'' function instead of the '''seq''' command as we did in BASH to generate the number of loops needed.</li>		There are a couple of differences to note when comparing this with the similar BASH script we created. First, instead of using a separate program, like the BASH '''read''' program, we are obtaining user input with the ''input()'' function. This program is then storing the user's input into a certain variable. By default the ''input()'' function saves information as a STRING which is a type of variable which can hold letters and numbers but can't be used for numeric operations like adding, subtracting, looping, etc. Because of this we use the ''int()'' and ''str()'' funtions to switch the data back and forth from the string type to the integer numeric type as needed in various parts of the script. Second, the for statement is using the built-in ''range()'' function instead of the '''seq''' command as we did in BASH to generate the number of loops needed.</li>
	* Try running the script and see if you were correct about what it does and how it works.		* Try running the script and see if you were correct about what it does and how it works.
	<~~li> The script as provided does not actually produce the correct number of files requested by the user. See if you can fix the script to produce the correct number of files.</li>~~		<ul>''NOTE: Also, it is important to note that while this script mostly works, it's just a simple example and not well written because it is easily broken by the user entering something other than a number for the number of files to be created, etc. A better script could be written to check for all of these things as well as other errors. If the script is to be used by more people than the original author (and in the best cases, even then) it is important for usability and security purposes to do these sorts of checks, particularly if the script accepts user input! This is how security bugs are born.''</ul>
	~~<li~~> Also, it is important to note that while this script mostly works, it's just a simple example and not well written because it is easily broken by the user entering something other than a number for the number of files to be created, etc. A better script could be written to check for all of these things as well as other errors. If the script is to be used by more people than the original author (and in the best cases, even then) it is important for usability and security purposes to do these sorts of checks, particularly if the script accepts user input! This is how security bugs are born.</li>		* See if you can modify the script so you can specify a starting and an ending number for the files rather than just a number of files to be created.
	~~<li>~~ See if you can modify the script so you can specify a starting and an ending number for the files rather than just a number of files to be created.~~</li>~~		* See if you can add a check to the script which will display an example of a filename that will be created and asking the user if that looks correct before actually creating all the files. If the user enters N then do not create the files. Hint, you will need to do a little research on using python IF statements to check user input.
	~~<li>~~ See if you can add a check to the script which will display an example of a filename that will be created and asking the user if that looks correct before actually creating all the files. If the user enters N then do not create the files. Hint, you will need to do a little research on using python IF statements to check user input.~~</li>~~
	</ol>		</ol>

KreidKolo: /* Using Loops and Reading User Input */

2021-02-16T00:34:20Z

Using Loops and Reading User Input

← Older revision		Revision as of 00:34, 16 February 2021
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	<ol>		<ol>
	<li> Create a ''file-generator.py'' script on your system like the one below and see if you can figure out how it works before testing it:		<li> Create a ''file-generator.py'' script on your system like the one below and see if you can figure out how it works before testing it:
	<pre>		<pre>#!/usr/bin/env python3
	#!/usr/bin/~~python~~
	import subprocess		import subprocess
	BASENAME="sample-file"		BASENAME = "sample-file"
	print "Welcome to the sample file generation utility!"		print("Welcome to the sample file generation utility!")
	print "Files will be created using the filename format "+BASENAME+"X.extension"		print("Files will be created using the filename format " + BASENAME + "X.extension")
	NUM = int(~~raw_input~~("Enter the number of files you wish to create, then press Enter: "))		NUM = int(input("Enter the number of files you wish to create, then press Enter: "))
	EXTENSION = ~~raw_input~~ ("Enter the extension (without the leading period) to put on the files: ")		EXTENSION = input("Enter the extension (without the leading period) to put on the files: ")
	for CURNUM in range(1,NUM):		for CURNUM in range(0, NUM):
	subprocess.call(["touch", BASENAME+str(CURNUM)+"."+EXTENSION])		subprocess.call(["touch", BASENAME + str(CURNUM) + "." + EXTENSION])
	print "Created "+str(NUM)+" file(s)."		print("Created " + str(NUM) + " file(s).")</pre>
	</pre>		There are a couple of differences to note when comparing this with the similar BASH script we created. First, instead of using a separate program, like the BASH '''read''' program, we are obtaining user input with the ''input()'' function. This program is then storing the user's input into a certain variable. By default the ''input()'' function saves information as a STRING which is a type of variable which can hold letters and numbers but can't be used for numeric operations like adding, subtracting, looping, etc. Because of this we use the ''int()'' and ''str()'' funtions to switch the data back and forth from the string type to the integer numeric type as needed in various parts of the script. Second, the for statement is using the built-in ''range()'' function instead of the '''seq''' command as we did in BASH to generate the number of loops needed.</li>
	There are a couple of differences to note when comparing this with the similar BASH script we created. First, instead of using a separate program, like the BASH '''read''' program, we are obtaining user input with the ''~~raw_input~~'' function. This program is then storing the user's input into a certain variable. By default the ''~~raw_input~~'' function saves information as a STRING which is a type of variable which can hold letters and numbers but can't be used for numeric operations like adding, subtracting, looping, etc. Because of this we use the ''int()'' and ''str()'' funtions to switch the data back and forth from the string type to the integer numeric type as needed in various parts of the script. Second, the for statement is using the built-in ''range()'' function instead of the '''seq''' command as we did in BASH to generate the number of loops needed.</li>		* Try running the script and see if you were correct about what it does and how it works.
	~~<li>~~ Try running the script and see if you were correct about what it does and how it works.~~</li>~~
	<li> The script as provided does not actually produce the correct number of files requested by the user. See if you can fix the script to produce the correct number of files.</li>		<li> The script as provided does not actually produce the correct number of files requested by the user. See if you can fix the script to produce the correct number of files.</li>
	<li> Also, it is important to note that while this script mostly works, it's just a simple example and not well written because it is easily broken by the user entering something other than a number for the number of files to be created, etc. A better script could be written to check for all of these things as well as other errors. If the script is to be used by more people than the original author (and in the best cases, even then) it is important for usability and security purposes to do these sorts of checks, particularly if the script accepts user input! This is how security bugs are born.</li>		<li> Also, it is important to note that while this script mostly works, it's just a simple example and not well written because it is easily broken by the user entering something other than a number for the number of files to be created, etc. A better script could be written to check for all of these things as well as other errors. If the script is to be used by more people than the original author (and in the best cases, even then) it is important for usability and security purposes to do these sorts of checks, particularly if the script accepts user input! This is how security bugs are born.</li>

KreidKolo: /* Using Variables and Conditionals in Python Scripts */

2021-02-16T00:20:58Z

Using Variables and Conditionals in Python Scripts

← Older revision		Revision as of 00:20, 16 February 2021
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	subprocess.call(["tar", "-czf", BACKUPFILE, "/home/"+USER])		subprocess.call(["tar", "-czf", BACKUPFILE, "/home/"+USER])
	print("Backup completed for "+USER+" saved to "+BACKUPFILE)</pre>		print("Backup completed for "+USER+" saved to "+BACKUPFILE)</pre>
	<li> Try running the above example and see if it works as you expect. This script used the output from the date command to get date information to be used as part of the filename but if you were actually writing the script in python you would probably use some of the python built in date functions instead. The advantages of doing it with the built-in functionality are that you will no longer be depending on the '''date''' program being installed on the system and you won't have to remove the newline from the end of the '''date''' output with the ''.rstrip()'' function, and you will just generally have cleaner code. After testing the above script and seeing how it works try modifying it like this to use built in date functionality:		<ul> Try running the above example and see if it works as you expect. This script used the output from the date command to get date information to be used as part of the filename but if you were actually writing the script in python you would probably use some of the python built in date functions instead. The advantages of doing it with the built-in functionality are that you will no longer be depending on the '''date''' program being installed on the system and you won't have to remove the newline from the end of the '''date''' output with the ''.rstrip()'' function, and you will just generally have cleaner code.</ul>
	<pre>		<li> After testing the above script and seeing how it works try modifying it like this to use built in date functionality:</li>
	#!/usr/bin/~~python~~		<pre>#!/usr/bin/env python3
	import subprocess		import subprocess
	import datetime		import datetime
	USER="jsmith"		USER = "jsmith"
	TODAY=datetime.date.today().strftime("%Y%m%d")		TODAY = datetime.date.today().strftime("%Y%m%d")
	BACKUPFILE="/var/"+USER+"-backup-"+TODAY+".tar.gz"		BACKUPFILE = "/var/"+USER+"-backup-"+TODAY+".tar.gz"
	print "Beginning backup for "+USER+" on "+TODAY		print("Beginning backup for "+USER+" on "+TODAY)
	subprocess.call(["tar", "-czf", BACKUPFILE, "/home/"+USER])		subprocess.call(["sudo", "tar", "-czf", BACKUPFILE, "/home/"+USER])
	print "Backup completed for "+USER+" saved to "+BACKUPFILE		print("Backup completed for "+USER+" saved to "+BACKUPFILE)</pre>
	</pre~~></li~~>		* See if you can predict what this script will do and then try it out to see if you are correct. Once you have figured out how this script works see if you can modify it so you can specify a username as an argument instead of as a fixed variable.
	~~<li>~~ See if you can predict what this script will do and then try it out to see if you are correct. Once you have figured out how this script works see if you can modify it so you can specify a username as an argument instead of as a fixed variable.~~</li>~~		* After successfully doing that try modifying the script so that it gives instructions about how to use the script if you forget to give a username as an argument.
	~~<li>~~ After successfully doing that try modifying the script so that it gives instructions about how to use the script if you forget to give a username as an argument.~~</li>~~		<ul> It is important to note that while these scripts work, they are just simple examples and not well written because they are easily broken by giving a username which doesn't actually exist on the system, or trying to backup files you don't have permission to access, etc. Better scripts could be written to check for all of these things as well as other errors. If the script is to be used by more people than the original author (and in the best cases, even then) it is important for usability and security purposes to do these sorts of checks, particularly if the script accepts user input such as an argument.</ul>
	<li> It is important to note that while these scripts work, they are just simple examples and not well written because they are easily broken by giving a username which doesn't actually exist on the system, or trying to backup files you don't have permission to access, etc. Better scripts could be written to check for all of these things as well as other errors. If the script is to be used by more people than the original author (and in the best cases, even then) it is important for usability and security purposes to do these sorts of checks, particularly if the script accepts user input such as an argument.</li>
	</ol>		</ol>

KreidKolo: /* Using Variables and Conditionals in Python Scripts */

2021-02-16T00:08:54Z

Using Variables and Conditionals in Python Scripts

← Older revision		Revision as of 00:08, 16 February 2021
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	<ol>		<ol>
	<li> Try adjusting your ''hello.py'' script to look like this:</li>		<li> Try adjusting your ''hello.py'' script to look like this:</li>
	<pre>#!/usr/bin/~~python~~		<pre>##!/usr/bin/env python3
	import sys		import sys
	print("The script you are running is: " + sys.argv[0])		print("The script you are running is: " + sys.argv[0])
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	<ul> It's also possible to capture the standard output of a command and put that into a variable for use just as we did with BASH. For example try running the '''date +%Y%m%d''' command. We can use the output of this command in a variable to make our backup script a little bit nicer. You'll also see that in order to capture the output we need to use the ''subprocess'' library instead of the ''os'' library we were using before. It's suggested that you switch to using the ''subprocess'' library anyway as the ''os.system'' function has been deprecated.</ul>		<ul> It's also possible to capture the standard output of a command and put that into a variable for use just as we did with BASH. For example try running the '''date +%Y%m%d''' command. We can use the output of this command in a variable to make our backup script a little bit nicer. You'll also see that in order to capture the output we need to use the ''subprocess'' library instead of the ''os'' library we were using before. It's suggested that you switch to using the ''subprocess'' library anyway as the ''os.system'' function has been deprecated.</ul>
	<li>Save this script as ''better-backup.py'' with the appropriate permissions to run it as a script:</li>		<li>Save this script as ''better-backup.py'' with the appropriate permissions to run it as a script:</li>
	<pre>#!/usr/bin/~~python~~		<pre>#!/usr/bin/env python3
	import subprocess		import subprocess
	USER = "jsmith"		USER = "jsmith"

KreidKolo: /* Using Variables and Conditionals in Python Scripts */

2021-02-16T00:07:44Z

Using Variables and Conditionals in Python Scripts

← Older revision		Revision as of 00:07, 16 February 2021
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	<ul>Wait, what if someone doesn't know they are supposed to include their name as an argument though? Try running '''./hello.py''' and see what happens. Unlike BASH Python is a little more particular about things and if you try to access a variable that doesn't exist it will give you an error. This isn't very user friendly so let's add a conditional to check and see if an argument was supplied or not.</ul>		<ul>Wait, what if someone doesn't know they are supposed to include their name as an argument though? Try running '''./hello.py''' and see what happens. Unlike BASH Python is a little more particular about things and if you try to access a variable that doesn't exist it will give you an error. This isn't very user friendly so let's add a conditional to check and see if an argument was supplied or not.</ul>
	<li> Try updating your ''hello.py'' script again and adding a conditional like this:		<li> Try updating your ''hello.py'' script again and adding a conditional like this:
	<pre>#!/usr/bin/~~python~~		<pre>#!/usr/bin/env python3
	import sys		import sys

KreidKolo: /* Creating Simple Python Scripts */

2021-02-16T00:07:36Z

Creating Simple Python Scripts

← Older revision		Revision as of 00:07, 16 February 2021
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	<li> Create a new text file named ''hello.py'' with the following text:</li>		<li> Create a new text file named ''hello.py'' with the following text:</li>
	<ul>''NOTE: that we are now using the ''.py'' extension so we can remember this is a Python instead of a BASH script.''</ul>		<ul>''NOTE: that we are now using the ''.py'' extension so we can remember this is a Python instead of a BASH script.''</ul>
	<pre>#!/usr/bin/~~python~~		<pre>#!/usr/bin/env python3
	print("Hello World from Python!")</pre>		print("Hello World from Python!")</pre>
	* Set the ''hello.py'' file to be executable by all users on the system so that we will be able to run it and then try running the script.		* Set the ''hello.py'' file to be executable by all users on the system so that we will be able to run it and then try running the script.
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	<ul> That said, it's still possible to run system commands from inside of a Python script as well (that's what ultimately makes them useful for shell scripting purposes after all. To do this we will need to import a special library of functions that Python can use to interact with the underlying system.</ul>		<ul> That said, it's still possible to run system commands from inside of a Python script as well (that's what ultimately makes them useful for shell scripting purposes after all. To do this we will need to import a special library of functions that Python can use to interact with the underlying system.</ul>
	<li>Try modifying your hello.py file like this:</li>		<li>Try modifying your hello.py file like this:</li>
	<pre>#!/usr/bin/~~python~~		<pre>#!/usr/bin/env python3
	import os		import os
	print("Hello World from Python!")		print("Hello World from Python!")

KreidKolo: /* Using Variables and Conditionals in Python Scripts */

2021-02-15T07:46:52Z

Using Variables and Conditionals in Python Scripts

← Older revision		Revision as of 07:46, 15 February 2021
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	<ul> See if you can predict what these changes will do and then try it out to see if you are correct. Because python stores all of the arguments into a special type of variable which can hold multiple pieces of data, called an array, we can use the ''len()'' function to check the length of the ''sys.argv'' array. If it's more than one (because ''sys.argv[0]'' always holds the script name so there is always at least one) we know arguments have been added. If not we know they have not been added. You'll also notice that indenting properly is important in Python scripts this is how python knows if a line is part of the if/else statement or something that comes after it.</ul>		<ul> See if you can predict what these changes will do and then try it out to see if you are correct. Because python stores all of the arguments into a special type of variable which can hold multiple pieces of data, called an array, we can use the ''len()'' function to check the length of the ''sys.argv'' array. If it's more than one (because ''sys.argv[0]'' always holds the script name so there is always at least one) we know arguments have been added. If not we know they have not been added. You'll also notice that indenting properly is important in Python scripts this is how python knows if a line is part of the if/else statement or something that comes after it.</ul>
	<ul> It's also possible to capture the standard output of a command and put that into a variable for use just as we did with BASH. For example try running the '''date +%Y%m%d''' command. We can use the output of this command in a variable to make our backup script a little bit nicer. You'll also see that in order to capture the output we need to use the ''subprocess'' library instead of the ''os'' library we were using before. It's suggested that you switch to using the ''subprocess'' library anyway as the ''os.system'' function has been deprecated.</ul>		<ul> It's also possible to capture the standard output of a command and put that into a variable for use just as we did with BASH. For example try running the '''date +%Y%m%d''' command. We can use the output of this command in a variable to make our backup script a little bit nicer. You'll also see that in order to capture the output we need to use the ''subprocess'' library instead of the ''os'' library we were using before. It's suggested that you switch to using the ''subprocess'' library anyway as the ''os.system'' function has been deprecated.</ul>
	<li>Save this script as ''better-backup.py'' with the appropriate permissions to run it as a ~~scrip~~:.</li>		<li>Save this script as ''better-backup.py'' with the appropriate permissions to run it as a script:</li>
	<pre>#!/usr/bin/python		<pre>#!/usr/bin/python
	import subprocess		import subprocess