COMP2718 Lab

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 at the end of the lab period.

Command Line Expansion and Substitution

Solve the following questions using some of the text tools: ls, cat, grep, sort, uniq, head, and tail and the commands date, pwd, and echo and command line expansion. All of the questions can be solved with one command line.

Write a command line that produces:
```
The product of 3 times 45 is 135.
```
An arithmetic expansion must be used to calculate 135. (hint: at least use echo)

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Make a directory name ~/tmp/a. Provide a command line that produces the following (assume the current directory is ~/tmp/a). The current month, day, and year should also be displayed.
```
At January 21, 2015 the current directory is ~/tmp/a.
```
You must employ echo, date, and pwd.

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Change into the directory containing the words1 -- words5 files (see lab 2). Write a command line that produces:
```
The number of occurrences of 'xy' in word1 is 102
```
The command should search word1 with grep for xy. (hint: use grep -c with other commands)

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Change into the directory containing the words1 -- words5 files (see lab 2). Write a command line that produces:
```
The string 'xy' appears in words1 and words2 197 times.
```
(hint: use an arithmetic expansion)

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Change into the directory containing the words file. Write a command line that produces:
```
The number of occurrences of 'st' in the first 100 lines of words is 3.
```
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History

Documentation about history expansion is found by man bash and search for HISTORY EXPANSION.

In a terminal window, execute the following commands:

% history -c
% cd $HOME
% mkdir testA
% cd testA
% echo "Time $(date +'%H:%M')" >> log
% echo "-----" >> log
% echo "Second Time $(date +'%H:%M')" >> log

Please type no other commands for the moment.

Determine what command gets executed by:
```
% !!
```
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Determine what command gets executed by:
```
% !-2
```
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Save your history with the command:
```
% history -w
```
Provide a command line to count the number of echo commands in the ~/.bash_history file. Do not use wc.

Command:

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Command(s) Output:

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Provide a command line show all the echo commands in the ~/.bash_history file.

Command:

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Command(s) Output:

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What history expansion command would search backwards for the most recent mkdir command?

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What key on the keyboard can be struck to display the last command and then allow the command to be edited?

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Permissions

Show the command(s) and their output used to determine the following:

The permissions and location of the sudo command (hint: use which to determine the location).

Command(s):

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Command(s) Output:

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The permissions and location of the ps command.

Command(s):

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Command(s) Output:

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Execute the following commands
```
% mkdir $HOME/test-3; cd $HOME/test-3;
% echo "Time: $(date +'%H:%M') $(pwd)" > ts
% chmod ugo-rwx ts
% chmod u+r ts
```
Show the command and its output used to determine the contents of ts.

Command:

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Command(s) Output:

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Show the command and output used to determine the permissions of ts.

Command:

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Command(s) Output:

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What command would change the permission to allow all users read access? Use the non-octal options for chmod.

Command:

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Show the new permissions:

Command:

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Command(s) Output:

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What is the octal version of this chmod command?

Command:

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Execute the following commands:
```
% cd /tmp
% mkdir -p /tmp/dir1/dir2
% chmod a-w  /tmp/dir1
% rmdir /tmp/dir1/dir2
```
Explain why the rmdir command fails. What permission should be changed to allow the rmdir command to succeed?

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