COMP2718 Assignment 3

Your Name -- Your Student Number

Complete this assignment by downloading this HTML file and editing it (using a text editor---not a special HTML editor). Wherever you see emphasized text (e.g. "Your name" and "Your Student Number" above) you should insert your own text, as appropriate. Submit via D2L by 2:15 p.m. on Monday, February 8.

Copy and Link

Consider the following commands used to make a backup of a file:

$ # version 1
$ mkdir backup
$ cp foo backup/foo
$ # version 2
$ mkdir backup
$ ln foo backup/foo

Which version is more efficient, justify your answer. Are there any disadvantages?

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Operations on Directories

Assume x is a file, and d is a directory, both in the current directory, describe what happens to the directories . (i.e., the current directory) and d when each of the following commands are executed (the commands are independent). You should state what entries are deleted, changed, or added to each directory.

1. $ mv x y

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2. $ mv x d

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3. $ mv x d/y

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Echo and Globbing

In a terminal window, enter the following:

$ mkdir foo; cd foo
$ touch ab abc de.txt h1.class h3.class

What is output by the following commands:

1. $ echo h*

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2. $ echo *[bs]

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3. $ echo *cl*

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4. $ echo [ad]*

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Types of Commands

Determine the type (using type) of the following commands. If the command is built in, can you suggest a possible reason why? Usually this relates to information contained within the shell itself.

1. cd

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2. type

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3. history

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4. ls

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5. man

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Redirection

Using redirection give the command line that changes echo hi there to:

1. save the standard output to the file fred.

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2. append the standard output to fred.

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3. write both standard output and error to sue

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4. The same as the previous question using the alternate syntax

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5. write standard error to err and discard the standard output to /dev/null.

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Shell Expansion

Using the shell expansion ability:

1. write one command that creates the directories: cs2718/assign1, cs2718/assign2, and cs2718/assignX. Do not assume cs2718 exists.

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2. write one command that creates the directories: cs2718/assign1/data, cs2718/assign2/data, cs2718/assignX/data. Do not assume any of the directories exist.

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3. write one command that creates the empty files: a0, a1, a2, a3, a4, a5, a6, a7, and a8. You must use brace expansion.

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More Shell Expansion

How does bash expand the following command line arguments (assume you are using Ubuntu 14.04 in the lab):

1. $HOME

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2. "$HOME/afile"

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3. "$USER"

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4. $PATH

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Command Substitution

A file called checkthis is created with:

$ echo -e "ls\ncd\ndf\nhistory" > checkthis

1. Write one command line that uses command substitution to determine the command type, with type, for each command on a separate line from the file checkthis. Show the command line's output.

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2. Write one command line that uses command substitution to determine the location of the commands listed in checkthis. Show the command line's output. Explain the output.

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