COMP 3000 Lab 1 2012 - Revision history

Soma: /* Answers */

2012-10-10T17:21:13Z

Answers

← Older revision		Revision as of 17:21, 10 October 2012
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	## A shell function. These are miniature shell scripts incorporated into the environment. We will cover configuring the environment and writing shell functions in later chapters, but for now, just be aware that they exist.		## A shell function. These are miniature shell scripts incorporated into the environment. We will cover configuring the environment and writing shell functions in later chapters, but for now, just be aware that they exist.
	## An alias. Commands that we can define ourselves, built from other commands.		## An alias. Commands that we can define ourselves, built from other commands.
	# /usr/bin and /usr/sbin, which [external command] for ~~example:~~ which ls		# /usr/bin and /usr/sbin and other directories. Run "echo $PATH" to see list of directories. Also, which [external command] will tell you path for specific commands, e.g. "which ls"
	# less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		# less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
	# touch "empty file.txt"		# touch "empty file.txt"

Soma: /* Answers */

2012-10-10T17:19:03Z

Answers

← Older revision		Revision as of 17:19, 10 October 2012
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	# bare metal (lambda) or virtualbox (virtualized)		# bare metal (lambda) or virtualbox (virtualized)
	# System administrators, level of access is restricted user		# System administrators, level of access is restricted user
			#
	## An executable program like all those files we saw in /usr/bin. Within this category, programs can be compiled binaries such as programs written in C and C++, or programs written in scripting languages such as the shell, perl, python, ruby, etc.		## An executable program like all those files we saw in /usr/bin. Within this category, programs can be compiled binaries such as programs written in C and C++, or programs written in scripting languages such as the shell, perl, python, ruby, etc.
	## A command built into the shell itself. bash supports a number of commands internally called shell builtins. The cd command, for example, is a shell builtin.		## A command built into the shell itself. bash supports a number of commands internally called shell builtins. The cd command, for example, is a shell builtin.

Soma: /* Answers */

2012-10-10T17:18:34Z

Answers

← Older revision		Revision as of 17:18, 10 October 2012
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	# bare metal (lambda) or virtualbox (virtualized)		# bare metal (lambda) or virtualbox (virtualized)
	# System administrators, level of access is restricted user		# System administrators, level of access is restricted user
	# 1. An executable program like all those files we saw in /usr/bin. Within this		## An executable program like all those files we saw in /usr/bin. Within this category, programs can be compiled binaries such as programs written in C and C++, or programs written in scripting languages such as the shell, perl, python, ruby, etc.
	category, programs can be compiled binaries such as programs written in C and		## A command built into the shell itself. bash supports a number of commands internally called shell builtins. The cd command, for example, is a shell builtin.
	C++, or programs written in scripting languages such as the shell, perl, python,		## A shell function. These are miniature shell scripts incorporated into the environment. We will cover configuring the environment and writing shell functions in later chapters, but for now, just be aware that they exist.
	ruby, etc.		## An alias. Commands that we can define ourselves, built from other commands.
	2. A command built into the shell itself. bash supports a number of commands
	internally called shell builtins. The cd command, for example, is a shell builtin.
	3. A shell function. These are miniature shell scripts incorporated into the
	environment. We will cover configuring the environment and writing shell
	functions in later chapters, but for now, just be aware that they exist.
	4. An alias. Commands that we can define ourselves, built from other commands.
	# /usr/bin and /usr/sbin, which [external command] for example: which ls		# /usr/bin and /usr/sbin, which [external command] for example: which ls
	# less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		# less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.

Soma: /* Answers */

2012-10-10T17:16:05Z

Answers

Afry at 21:35, 7 October 2012

2012-10-07T21:35:10Z

← Older revision		Revision as of 21:35, 7 October 2012
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	8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
	9. touch "empty file.txt"		9. touch "empty file.txt"
	10. cat empty\ file.txt or cat "empty file.txt" or cat 'empty file.txt'		10. cat empty\ file.txt or cat "empty file.txt" or cat 'empty file.txt' or > 'empty file.txt'

	Part B		Part B

Afry at 16:20, 7 October 2012

2012-10-07T16:20:28Z

← Older revision		Revision as of 16:20, 7 October 2012
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	8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
	9. touch "empty file.txt"		9. touch "empty file.txt"
	10. cat empty\ file.txt or cat "empty file.txt"		10. cat empty\ file.txt or cat "empty file.txt" or cat 'empty file.txt'

	Part B		Part B

Afry at 15:41, 7 October 2012

2012-10-07T15:41:57Z

← Older revision		Revision as of 15:41, 7 October 2012
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	functions in later chapters, but for now, just be aware that they exist.		functions in later chapters, but for now, just be aware that they exist.
	4. An alias. Commands that we can define ourselves, built from other commands.		4. An alias. Commands that we can define ourselves, built from other commands.
	7. /usr/bin and /usr/sbin, which ls		7. /usr/bin and /usr/sbin, which [external command] for example: which ls
	8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
	9. touch "empty file.txt"		9. touch "empty file.txt"

Afry at 14:47, 7 October 2012

2012-10-07T14:47:05Z

← Older revision		Revision as of 14:47, 7 October 2012
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	8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
	9. touch "empty file.txt"		9. touch "empty file.txt"
	10. cat empty\ file.txt		10. cat empty\ file.txt or cat "empty file.txt"

	Part B		Part B

Afry at 14:16, 7 October 2012

2012-10-07T14:16:52Z

← Older revision		Revision as of 14:16, 7 October 2012
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	== Answers ==		== Answers ==
			Answer key for lab 1:

	1. *(check against actual username list)		1. *(check against actual username list)
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	functions in later chapters, but for now, just be aware that they exist.		functions in later chapters, but for now, just be aware that they exist.
	4. An alias. Commands that we can define ourselves, built from other commands.		4. An alias. Commands that we can define ourselves, built from other commands.
	7. /usr/bin and /usr/sbin		7. /usr/bin and /usr/sbin, which ls
	8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
	9. touch "empty file.txt"		9. touch "empty file.txt"

Afry at 13:58, 7 October 2012

2012-10-07T13:58:17Z

← Older revision		Revision as of 13:58, 7 October 2012
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	# [2] With the <tt>&</tt> you can put processes in the "background". Given that external commands are always run as separate processes from the command shell, what is the key difference between foreground and background processes?		# [2] With the <tt>&</tt> you can put processes in the "background". Given that external commands are always run as separate processes from the command shell, what is the key difference between foreground and background processes?
	# [2] What are the differences between shell and environment variables? Specifically, what processes have each of them, and to what extent are they shared? HINT: look at the <tt>execve</tt> system call.		# [2] What are the differences between shell and environment variables? Specifically, what processes have each of them, and to what extent are they shared? HINT: look at the <tt>execve</tt> system call.

			== Answers ==

			1. *(check against actual username list)
			2. should be: Ubuntu 12.04 LTS unless specifically stated reason otherwise
			3. /bin/bash SCS gives csh as the default shell
			4. bare metal (lambda) or virtualbox (virtualized)
			5. System administrators, level of access is restricted user
			6. 1. An executable program like all those files we saw in /usr/bin. Within this
			category, programs can be compiled binaries such as programs written in C and
			C++, or programs written in scripting languages such as the shell, perl, python,
			ruby, etc.
			2. A command built into the shell itself. bash supports a number of commands
			internally called shell builtins. The cd command, for example, is a shell builtin.
			3. A shell function. These are miniature shell scripts incorporated into the
			environment. We will cover configuring the environment and writing shell
			functions in later chapters, but for now, just be aware that they exist.
			4. An alias. Commands that we can define ourselves, built from other commands.
			7. /usr/bin and /usr/sbin
			8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
			9. touch "empty file.txt"
			10. cat empty\ file.txt

			Part B
			1. Some require direct access to kernel functions and therefore must be built in. Also the built in functions operate faster than non built in functions.
			This is either for performance reasons -- builtins execute faster than external commands, which usually require forking off a separate process -- or because a particular builtin needs direct access to the shell internals.

			2. drwx------

			d = a directory flag - since my home directory is a directory, there exists a d here
			rwx = read, write, execute permission for the User (owner of the directory) which is my username
			--- = read write execute permissions are lacking for a Group
			--- = read write execute permissions are lacking for other

			this means my work is private. Only myself and the root user can access my directory.

			3. cat file.txt \| grep hello

			the \| character joins the two commands cat and grep, it enables the output from one command to be passed directly to another.

			cat file.txt > error.txt

			the > character redirects the standard output to the specified filename that is included in the command after it. If the file is not created it will create it, if the file exists it will overwrite the current file

			cat file.txt > alreadyexistingerrorfile.txt

			the >> character appends to the already existing file the output of the first command.

			cat < file.txt is equivalent to cat file.txt

			the < character redirects the standard input to come from the file instead

			the last form of redirection is only useful within shell scripts to avoid having to code a bunch of echo statements, say for a particular menu. The document created is called a here document. It is a method of specifying a string literal in command line shells. (preserves line breaks and whitespaces / indentation within the text.)

			example:

			# present a menu
			cat << alldone
			What would you like to do today?
			Play with shell scripts
			Write wonderful awk scripts
			Invent powerful sed scripts
			zippity do and dah
			alldone

			the above code will generate the following output:

			What would you like to do today?
			Play with shell scripts
			Write wonderful awk scripts
			Invent powerful sed scripts
			zippity do and dah

			otherwise you would have had to code echo statements for each line.

			4. STDERR does not have a dedicated redirection operator, instead to redirect stderr you have to refer to it's file descriptor. and call it using 2>

			5. the other file descriptors are 0 for standard in and 1 for standard out, the descriptor number is placed right before the redirection operator.

			6.for variable [in words]; do
			commands
			done

			variable is the name of a variable that will increment during the execution of the loop, words is an optional list of items that will be sequentially assigned to the variable, and commands are the list of commands to be executed on each iteration of the loop.

			for i in A B C D; do echo $i; done

			7. x=5
			if [ $x = 5 ]; then
			echo "x equals 5."
			else
			echo "x does not equal 5."
			fi

			x=5
			if [ $x = 5 ]; then echo "equals 5"; else echo "does not equal 5"; fi

			if commands; then
			commands
			[elif commands; then
			commands...]
			[else
			commands]
			fi
			where commands is a set of commands. Providing an exit status that indicates success or failure.

			8. Background processes usually interact with the system and do not interact with the shell or the user, foreground processes must interact with the command shell. In the shell, background and foreground processes are the same except that the shell waits for foreground processes to finish before giving a new prompt.

			9. shell variables apply only to the current shell. Environment variables apply to all possible shells running on the system. to list all env variables type printenv to list all shell variables use set
			a shell variable is local to a particular instance of the shell (such as a shell script), while environment variables are "inherited" by any program you start, including another shell
			That is, the new process gets its own copy of these variables, which it can read, modify, and pass on in turn to its own children. In fact, every UNIX process (not just the shell) passes its environment variables to its child processes.

← Older revision		Revision as of 17:16, 10 October 2012
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	Answer key for lab 1:		Answer key for lab 1:

	1. *(check against actual username list)		# *(check against actual username list)
	2. should be: Ubuntu 12.04 LTS unless specifically stated reason otherwise		# should be: Ubuntu 12.04 LTS unless specifically stated reason otherwise
	3. /bin/bash SCS gives csh as the default shell		# /bin/bash SCS gives csh as the default shell
	4. bare metal (lambda) or virtualbox (virtualized)		# bare metal (lambda) or virtualbox (virtualized)
	5. System administrators, level of access is restricted user		# System administrators, level of access is restricted user
	6. 1. An executable program like all those files we saw in /usr/bin. Within this		# 1. An executable program like all those files we saw in /usr/bin. Within this
	category, programs can be compiled binaries such as programs written in C and		category, programs can be compiled binaries such as programs written in C and
	C++, or programs written in scripting languages such as the shell, perl, python,		C++, or programs written in scripting languages such as the shell, perl, python,
Line 50:		Line 50:
	functions in later chapters, but for now, just be aware that they exist.		functions in later chapters, but for now, just be aware that they exist.
	4. An alias. Commands that we can define ourselves, built from other commands.		4. An alias. Commands that we can define ourselves, built from other commands.
	7. /usr/bin and /usr/sbin, which [external command] for example: which ls		# /usr/bin and /usr/sbin, which [external command] for example: which ls
	8. less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.		# less allows backward movement within the file as well as forward movement. more is a rudimentary method for printing to crt terminals, but only allows movement through the file in a forward direction. You have to press 'q' to exit less, but more quits when it reaches EOF.
	9. touch "empty file.txt"		# touch "empty file.txt"
	~~10.~~ cat empty\ file.txt or cat "empty file.txt" or cat 'empty file.txt' or > 'empty file.txt'		# cat empty\ file.txt or cat "empty file.txt" or cat 'empty file.txt' or > 'empty file.txt'

	Part B		Part B