IT 244: Introduction to Linux/Unix

IT 244: Introduction to Linux/Unix
Class 5

Microphone

Questions

Are there any questions before I begin?

Readings

If you have the textbook you should read chapter 3, The Utilities.

Homework 3

I have posted homework 3.

As usual, it will be due this coming Sunday at 11:59 PM.

Today's Class

In today's class I will continue talking about utilities.

And discuss command completion which can save you time and effort.

General Advice

Learn to Read Carefully

Most of us spend a large part of each day reading
Most of this reading is done quickly ...
because the material is familiar ...
and the details are not that important
Most of the time when we read, we know what to expect
For example, if you get a text from a friend ...
you don't linger over each word
You have some idea of what your friend is going to say ...
so you can read it quickly
The same thing happens if you read the about your favorite singer
The details aren't important ...
just the overall picture
The reading you must do for this course ...
is fundamentally different
Technical work is detailed work
If you read technical material too quickly ...
you will miss important details
You must learn to read technical material slowly and carefully
You will sometime have to read something a second or third time ...
until you fully understand it
Learning how to read technical material ...
may be the most important thing you take away from this class

Course Work

Graded Quiz Today

After I finish my lecture today I will hand out papers for today's graded quiz
Write your name clearly at the top
When you finish the Quiz hand it to me
Then you can work on the Class Exercise

Late Penalty

You will lose 2 points for every day that your assignment is late
Every Unix file has a time stamp that changes every time the file is modified
My scripts look at this date stamp to determine whether a submission is late
If your assignment is not working by the due date ...
you can continue to work on it ...
but you will lose a few points
If your assignment is working, do not go back and change it
Any changes you make will change the date stamp ...
which will cost you points

Do Not Email Me about Missing Assignments

If you get an email from me saying an assignment is missing
do not email me about this
I get far too many emails
Instead of sending me an email, fix the problem
If you do not know how to fix it
- Come to Zoom Office Hours
- Post a question of Piazza
- Contact the Class Assistant
I collect homework assignments and check Class Exercises several times during the week
I will check or collect your assignment later in the week.

Importance of Exams

Many people find exams difficult
But the best way for me to know if you have really learned the material is by giving exams
It is too easy to cheat on Class Exercises and homework assignments
This is why the two exams account for 50% of your grade
Too many students do well on the graded quizzes, Class Exercises and homework assignment ...
only to do poorly on the exams
This lowers their grade considerably
The purpose of the Class Exercises and homework assignments is to give you hands on experience with the material ...
and to better prepare you for the exams

Preparing for Exams

Both the midterm and final exams follow the same format
60% of the points on the exams come from questions taken from the ungraded class quizzes
The remaining 40% of the points come from other questions created specially for the exam
Two things will help you prepare for exams
- Flash cards
- Class Exercises and homework assignments
Flash cards should be made for all questions from Ungraded Class Quizzes
You should review them frequently throughout the semester
Pay attention when you are working on the Class Exercises and homeworks
Work on these assignments is teaching much about the Linux command line
This will come in handy for answering the questions that do not come from the Ungraded Class Quizzes

Shell Scripts for Homework Assignments

Starting with homework 3, you will need to write shell scripts for all homework assignments
This makes it easier for me to grade your homework
These script files must meet certain requirements or you will lose points
I've created a document which lists the requirements for scripts
You will find it here
Let's look at them

Scripts for Class Exercises

Starting today, all Class Exercises will ask you to also write scripts
You do not have to follow all the requirements for homework scripts for Class Exercise scripts
But there are a few thing you should not do in these scripts
Do not do any of the following
- Run man or info
- Run more or less
- Run nano, vi, vim, emacs or any text editors
All these commands ask the user for input
I run scripts to check your Class Exercises
If you use any of the commands above in your Class Exercise scripts ...
my test scripts will not run the way they should
You will get no credit for the assignment until you remove these commands

Tips and Examples

Do Not Fall Behind in This Course

Technical courses require that you master a great deal of detail
You will need to study for this course several times during the week
Studying once a week is usually not enough
The key to success in a technical course is steady, consistant, work
It should be spread out over several days
Some important concepts do not sink in immediately
It may take several days for something new to become clear
Material in this course often depends on what came before
So it is critical that you not fall behind
If you fall behind, it can be VERY hard to catch up

Read the Homework Assignments Carefully

Homework assignments may ask you to do many things
So you may need to read the assignment more than once
A single reading might not be enough to understand what I want you to do
Take the time to read these documents slowly
This will help you understand all the details
If you don't, you will make mistakes and lose points
Technical work is detailed work
So you must learn to read documents with a lot of detail
If you do not understand something post a question on Piazza
NEVER GUESS at the meaning of something I have written

Working with More than One Window

You can have more that one ssh window open at any one time
I normally run at least 4 ssh sessions on my Mac
Each one of these windows is a separate login session
If you close one of these windows it does not affect the others

Shell Scripts

The commands you type at the command line can be placed in a text file
That file can then be run and all the commands will be executed
Such a file is called a shell script
Here is a shell script that first goes to my home directory
Then it goes to my tmp directory ...
and lists its contents
```
cd
cd tmp
ls
```
If the name of the script file is tmp.sh I can run it like this
```
bash tmp.sh
```

Review

Special Characters

There are some characters that have special meaning in Unix
They should not be used in file or directory names

They are

& : | * ? ' " [ ] ( ) $ < > { } # / \ ! ~

Three other characters, called whitespace, are also special
The whitespace characters are
- Space
- Tab
- Newline
Spaces are used to separate entries on the command line
They separate the command from its options and its arguments
Tab has a special meaning we will discuss later today
The newline character is what you get when you hit Enter on a PC ...
or Return on a Mac
When you are typing in a text editor ...
the newline moves you down to the next line
On the command line, hitting Enter or Return tells the shell ...
you are done typing a command ...
and the shell should run the command you just entered
You don't have to be at the end of the command line ...
to hit Enter to run the command

Quoting and Escaping

If you cannot avoid using a special character as an argument ...
you must do one of two things
- Use quotes
- Escape the special character
Escaping means putting a backslash, \ , in front of a special character
This turn off the special meaning of the character
The backslash must come immediately in front of the special character
There are two types of quotes
Single quotes - ' '
Double quotes - " "
They have slightly different effcts ...
but you don't need to worry about the difference for now

`pwd` - Show Your Current Directory

pwd (print working directory) shows your current directory
```
pwd
```

`cd` - Change Directory

cd (change directory) changes your current directory
You use cd to move from one directory to another
```
cd DIRECTORY_NAME
```
If you use cd with an argument it moves you to that directory
If you use cd without an argument ...
it takes you to your home directory
To go up one directory, use ..
```
cd ..
```
To go up more than one directory use multiple instances of ..
Each .. must be separated by a /
To go up two directories enter
```
cd ../..
```

`ls` - List the Contents of a Directory

ls shows you the files and directories inside a directory
You can use ls with or without an argument
If you give ls a directory name ...
it lists what is inside that directory
When you don't give ls an argument ...
it lists the current directory
Like many Unix commands ls has multiple options
But two are used most often

The -l (el) option gives you a long listing

$ ls -l
total 20
-rw-rw-r--   1 ghoffman       103 Sep 11 14:34 basic.css
-rw-r--r--   1 ghoffman      3560 Aug 29 13:30 emacs_cheat_sheet.html
-rw-r--r--   1 ghoffman       701 Aug 29 13:30 index.html
drwxr-xr-x   6 ghoffman       512 Sep 15 14:11 it_244
-rw-r--r--   1 ghoffman      6831 Aug 29 13:30 tips.html
-rw-r--r--   1 ghoffman      6052 Aug 29 13:30 unix_cheat_sheet.html

The -a (for all) option also lists files whose names begin with . (dot)
These "invisible" files contain Unix configuration information

`cat` - Print the Contents of a File

cat (concatenate) prints a file
```
$ cat foo.txt 
foo
bar
blecth
```

When used with the -n option, cat displays line numbers

$ cat -n numbered_lines.txt 
     1  Line 1
     2  Line 2
     3  Line 3
     4  Line 4
     5  Line 5

`rm` - Delete a File

rm (remove) deletes a file
```
rm FILENAME
```
There is no undelete feature in Unix
To remove all the files in a directory use
```
rm *
```

`mkdir` - Create a Directory

mkdir (make directory) creates a directory
```
mkdir DIRECTORY_NAME
```
The directory will be created in the current directory

`rmdir` - Delete a Directory

rmdir (remove directory) deletes a directory
```
rmdir DIRECTORY_NAME
```
rmdir will not work unless the directory is empty

`cp` - Copy Files

cp (copy) makes a copy of a file or a directory
```
cp  FILENAME  DIRECTORY_OR_NEW_FILENAME
```
cp takes two arguments
The first argument is the source
The file or directory to be copied
The second argument is the destination
Often the destination is a directory
If you are copying to the current directory ...
the destination is a new filename
To copy a directory you must use the -r option

`mv` - Move a File or Directory

mv (move) is a command that does two different things
It can change the location of a file or directory
```
mv  FILENAME_OR_DIRECTORY_NAME  NEW_DIRECTORY
```

It can also change the name of a file or directory

mv  FILENAME_OR_DIRECTORY_NAME  NEW_FILENAME_OR_NEW_DIRECTORY_NAME

In either case, mv takes two arguments
The first argument is always the the name of the file or directory
When used to move, the the second argument is the new directory
When changing the name of a file or directory, the second is the new name

Attendance

New Material

`echo` - Print Text to the Terminal

echo simply prints whatever comes after it to the screen
```
$ echo Hello world!
Hello world!
```
It's used a lot in shell scripts ...
to let the user know what is happening

It is also useful for seeing the value of a variable

$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:...

When echo is used with the -n option it does not advance to the next line
But this only works inside scripts

`hostname` - Print the Name of Your Host Machine

Every machine on the network has a network name
This name is known as the hostname
The hostname command prints the network name ...
of the machine you are using
```
$ hostname
pe15
```
You might think this command is useless ...
because you always know what machine you are using
But if you have multiple ssh windows connecting to mutliple machines ...
this command can be a lifesaver
When used with the -i option hostname will print the IP address of the host machine
```
$ hostname -i
158.121.104.215
```
The -i option does not work on my Mac
Which is an example of how the Unix on Mac is slightly non-standard

Pagers - View a File One Screen at a Time

If I want to see what's in a file ...
I can use cat
But if the file is very long ...
most of it will spill off the top of the screen
Pagers give you another choice
Pagers show the contents of a file one screenful at a time
Unix provides two paging programs
- more
- less

`more`

more has been around for a long time
When you run more on a file ...
it shows you the first screenful
If you hit Enter or Return it will go down one line
If you hit the spacebar it will advance one screen down
At the bottom of the screen it shows you the percentage of the file ...
you have seen so far
If you keep hitting the spacebar ...
you will fall back to the command line
If you want to quit before that hit q
To see the previous page hit b
To see all possible commands hit h

`less`

less is an improved version of more
The name is an example of dry Unix humor
It's not more ...
it's less
Again you hit the spacebar to move down one screenful
To move down one line hit Enter
And b takes you back to the previous screen
But you can use the up arrow ↑ to go up a line
and ↓ to go the other way
If you get to the end of the file you must use q to quit
less is loaded with features
To search for text type ? ...
and then some characters
It will find the first of occurrence of the string
And n will take you to the next
To see the full list of features hit h
I would recommand you use less

Pathname Completion

Using the command line is hard
When you type something it must be absolutely correct ...
or you will get an error message
But modern shells like Bash have features ...
that make the command line a little easier to use
Consider the following situation
I am in a directory with the HTML files for Class Notes

The name of these files are very long

$ ls
01_class_notes_it116.html  22_class_notes_it116.html
02_class_notes_it116.html  23_class_notes_it116.html
03_class_notes_it116.html  24_class_notes_it116.html
04_class_notes_it116.html  25_class_notes_it116.html
05_class_notes_it116.html  26_class_notes_it116.html
...

If I wanted to run ls -l on the file for today's Class Notes ...

I would have to type

$ ls -l 05_class_notes_it116.html 
-rw-r--r-- 1 ghoffman faculty 35194 Apr 22 10:20 05_class_notes_it116.html

I'm a horrible typist
I call mysef fumble fingers
Trying to type that long filename exactly would not be easy
But I don't have too
All I have to do is type the first few letters of the filename ...
hit Tab ...
and Bash will complete the rest of the filename
This feature is called pathname completion
We'll talk more about pathnames in a future class
This feature saves me endless greif
But what if I type a few characters ...
and there is more than one filename that matches?
In that case Bash will beep
But if I hit Tab again it will beep again ...
and show me all possible matches

but it will also print my partial command again

$ ls -l 0
01_class_notes_it116.html  04_class_notes_it116.html  07_class_notes_it116.html
02_class_notes_it116.html  05_class_notes_it116.html  08_class_notes_it116.html
03_class_notes_it116.html  06_class_notes_it116.html  09_class_notes_it116.html

[516] (pe15) ghoffman - ~/public_html/it116_html/class_notes_it116
$ ls -l 0

so all I have to do is type enough additional characters ...
to specify the file I want
If there is no possible match ...
Bash will keep beeping

`grep` - Finding Strings inside Files

But my favorite Unix utility is grep
which stands for get regular expression
Regular expressions are an advanced topic ...
that I will mention briefly at the end of the semester
I can use grep to find every line in a file ...
that has a certain string
A string is a collection of characters that may, or may not, be a word

grep uses the following format

grep  [-OPTIONS]  SEARCH_STRING  FILE ...

The words in capital letters, OPTION, SEARCH_STRING and FILE are placeholders
They stand in place of a value that you have to provide
Anything enclosed in square brackets is optional
Here is an example of how grep can be used

Say we have a text file

$ cat  red_sox.txt 
2011-07-02      Red Sox @  Astros       Win 7-5
2011-07-03      Red Sox @  Astros       Win 2-1
2011-07-04      Red Sox vs Blue Jays    Loss 7-9
2011-07-05      Red Sox vs Blue Jays    Win 3-2
2011-07-06      Red Sox vs Blue Jays    Win 6-4
2011-07-07      Red Sox vs Orioles      Win 10-4
2011-07-08      Red Sox vs Orioles      Win 10-3
2011-07-09      Red Sox vs Orioles      Win 4-0
2011-07-10      Red Sox vs Orioles      Win 8-6
2011-07-15      Red Sox @  Rays         Loss 6-9
2011-07-16      Red Sox @  Rays         Win 9-5
2011-07-17      Red Sox @  Rays         Win 1-0
2011-07-18      Red Sox @  Orioles      Win 15-10
2011-07-19      Red Sox @  Orioles      Loss 2-6
2011-07-20      Red Sox @  Orioles      Win 4-0
2011-07-22      Red Sox vs Mariners     Win 7-4
2011-07-23      Red Sox vs Mariners     Win 3-1
2011-07-24      Red Sox vs Mariners     Win 12-8
2011-07-25      Red Sox vs Royals       Loss 1-3
2011-07-26      Red Sox vs Royals       Win 13-9
2011-07-27      Red Sox vs Royals       Win 12-5
2011-07-28      Red Sox vs Royals       Loss 3-4
2011-07-29      Red Sox @  White Sox    Loss 1-3
2011-07-30      Red Sox @  White Sox    Win 10-2
2011-07-31      Red Sox @  White Sox    Win 5-3

And we want to find all the games the Sox where winners

We can use grep like this

$ grep Win red_sox.txt 
2011-07-02      Red Sox @  Astros       Win 7-5
2011-07-03      Red Sox @  Astros       Win 2-1
2011-07-05      Red Sox vs Blue Jays    Win 3-2
2011-07-06      Red Sox vs Blue Jays    Win 6-4
2011-07-07      Red Sox vs Orioles      Win 10-4
2011-07-08      Red Sox vs Orioles      Win 10-3
2011-07-09      Red Sox vs Orioles      Win 4-0
2011-07-10      Red Sox vs Orioles      Win 8-6
2011-07-16      Red Sox @  Rays         Win 9-5
2011-07-17      Red Sox @  Rays         Win 1-0
2011-07-18      Red Sox @  Orioles      Win 15-10
2011-07-20      Red Sox @  Orioles      Win 4-0
2011-07-22      Red Sox vs Mariners     Win 7-4
2011-07-23      Red Sox vs Mariners     Win 3-1
2011-07-24      Red Sox vs Mariners     Win 12-8
2011-07-26      Red Sox vs Royals       Win 13-9
2011-07-27      Red Sox vs Royals       Win 12-5
2011-07-30      Red Sox @  White Sox    Win 10-2
2011-07-31      Red Sox @  White Sox    Win 5-3

grep is case sensitive
Just like the Unix command line
If we used "win" instead of "Win" we would get nothing
```
$ grep win red_sox.txt
```

If you want grep to ignore case you must run it with the -i option

$ grep -i win red_sox.txt 
2011-07-02      Red Sox @  Astros       Win 7-5
2011-07-03      Red Sox @  Astros       Win 2-1
2011-07-05      Red Sox vs Blue Jays    Win 3-2
2011-07-06      Red Sox vs Blue Jays    Win 6-4
2011-07-07      Red Sox vs Orioles      Win 10-4
2011-07-08      Red Sox vs Orioles      Win 10-3
2011-07-09      Red Sox vs Orioles      Win 4-0
2011-07-10      Red Sox vs Orioles      Win 8-6
2011-07-16      Red Sox @  Rays         Win 9-5
2011-07-17      Red Sox @  Rays         Win 1-0
2011-07-18      Red Sox @  Orioles      Win 15-10
2011-07-20      Red Sox @  Orioles      Win 4-0
2011-07-22      Red Sox vs Mariners     Win 7-4
2011-07-23      Red Sox vs Mariners     Win 3-1
2011-07-24      Red Sox vs Mariners     Win 12-8
2011-07-26      Red Sox vs Royals       Win 13-9
2011-07-27      Red Sox vs Royals       Win 12-5
2011-07-30      Red Sox @  White Sox    Win 10-2
2011-07-31      Red Sox @  White Sox    Win 5-3

If your search string contains one of Unix's special characters ...
you need to use a backslash, \ ...
or use quotes
grep -r will search recursively through a directory
That means it looks through the directory and all the subdirectories

grep -v returns all lines that do not match the search string

$ grep -v Win red_sox.txt 
2011-07-04      Red Sox vs Blue Jays    Loss 7-9
2011-07-15      Red Sox @  Rays         Loss 6-9
2011-07-19      Red Sox @  Orioles      Loss 2-6
2011-07-25      Red Sox vs Royals       Loss 1-3
2011-07-28      Red Sox vs Royals       Loss 3-4
2011-07-29      Red Sox @  White Sox    Loss 1-3

And grep -n lists line numbers

$ grep -n White red_sox.txt 
23:2011-07-29      Red Sox @  White Sox    Loss 1-3
24:2011-07-30      Red Sox @  White Sox    Win 10-2
25:2011-07-31      Red Sox @  White Sox    Win 5-3

There are many more useful options for grep
They can be found on the man page
I use grep on an almost daily basis
For example, let's say I want to add a field to a database table
I keep all my SQL code in text files
I can use grep to find every file that uses that particular table

`head` - View the Top of a File

Sometimes the first few lines of a file are all you need to see ...
to know the file is what you were looking for
You can you head to see the first few lines of the file
Running head without an argument

prints the first 10 lines of a file

$ head red_sox.txt 
2011-07-02      Red Sox @  Astros       Win 7-5
2011-07-03      Red Sox @  Astros       Win 2-1
2011-07-04      Red Sox vs Blue Jays    Loss 7-9
2011-07-05      Red Sox vs Blue Jays    Win 3-2
2011-07-06      Red Sox vs Blue Jays    Win 6-4
2011-07-07      Red Sox vs Orioles      Win 10-4
2011-07-08      Red Sox vs Orioles      Win 10-3
2011-07-09      Red Sox vs Orioles      Win 4-0
2011-07-10      Red Sox vs Orioles      Win 8-6
2011-07-15      Red Sox @  Rays         Loss 6-9

If you give head a number as an option it will display that number of lines

$ head -5 red_sox.txt 
2011-07-02      Red Sox @  Astros       Win 7-5
2011-07-03      Red Sox @  Astros       Win 2-1
2011-07-04      Red Sox vs Blue Jays    Loss 7-9
2011-07-05      Red Sox vs Blue Jays    Win 3-2
2011-07-06      Red Sox vs Blue Jays    Win 6-4

`tail` - View the Bottom of a File

tail is like head except it prints the last 10 lines of a file

$ tail red_sox.txt 
2011-07-22      Red Sox vs Mariners     Win 7-4
2011-07-23      Red Sox vs Mariners     Win 3-1
2011-07-24      Red Sox vs Mariners     Win 12-8
2011-07-25      Red Sox vs Royals       Loss 1-3
2011-07-26      Red Sox vs Royals       Win 13-9
2011-07-27      Red Sox vs Royals       Win 12-5
2011-07-28      Red Sox vs Royals       Loss 3-4
2011-07-29      Red Sox @  White Sox    Loss 1-3
2011-07-30      Red Sox @  White Sox    Win 10-2
2011-07-31      Red Sox @  White Sox    Win 5-3

You can give tail a number as an option to specify the number of lines printed

$ tail -4 red_sox.txt 
2011-07-28      Red Sox vs Royals       Loss 3-4
2011-07-29      Red Sox @  White Sox    Loss 1-3
2011-07-30      Red Sox @  White Sox    Win 10-2
2011-07-31      Red Sox @  White Sox    Win 5-3

tail is especially useful when looking at log files
Log files are text files that record significant events
They are created automatically by programs that provide services ...
like a web server
The most recent entries are at the end of a file
Those are usually the lines you want to see ...
when you are trying to solve a problem

`sort` - Print a File in Sorted Order

Another usefull utility for working with text files is sort

sort prints a file with the lines sorted

$ cat  fruit.txt 
grapes
pears
oranges
cranberries
apples
melons
blueberries

$ sort  fruit.txt 
apples
blueberries
cranberries
grapes
melons
oranges
pears

Note that sort does not change a file
It simply prints the lines of a file in a different order
sort prints the lines of a file in alphabetical order ...
unless you use one of its options

sort -r (reverse) will sort the file in reverse alphabetical order

$ sort -r fruit.txt 
pears
oranges
melons
grapes
cranberries
blueberries
apples

sort -n (number) will sort a file by numbers

So a line starting with "2" will appear before a line starting with "11"

$ cat numbers_jumbled.txt
11
1
17
2
3
15
4
5
14
6
13
7
8
9
10
12
16
18
19
20

$ sort numbers_jumbled.txt
1
10
11
12
13
14
15
16
17
18
19
2
20
3
4
5
6
7
8
9

$ sort -n numbers_jumbled.txt
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

To sort a file in reverse numerical order use -nr

$ sort -nr numbers_jumbled.txt
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1

Class Exercise 5

Class Exercise 5 is the first exercise where you will have to write a shell script.

You will create a text file using nano, and type the Linux commands into it.

You must create this file in your ex5 directory.

Please note that the first few sections of Class Exercise 5 should not be included in your ex5.sh script.

Test your script to see that it works.

General Advice

Course Work

Tips and Examples

Review

New Material

Questions

Readings

Homework 3

Today's Class

General Advice

Learn to Read Carefully

Course Work

Graded Quiz Today

Late Penalty

Do Not Email Me about Missing Assignments

Importance of Exams

Preparing for Exams

Shell Scripts for Homework Assignments

Scripts for Class Exercises

Tips and Examples

Do Not Fall Behind in This Course

Read the Homework Assignments Carefully

Working with More than One Window

Shell Scripts

Review

Special Characters

Quoting and Escaping

pwd - Show Your Current Directory

cd - Change Directory

ls - List the Contents of a Directory

cat - Print the Contents of a File

rm - Delete a File

mkdir - Create a Directory

rmdir - Delete a Directory

cp - Copy Files

mv - Move a File or Directory

Attendance

New Material

echo - Print Text to the Terminal

hostname - Print the Name of Your Host Machine

Pagers - View a File One Screen at a Time

more

less

Pathname Completion

grep - Finding Strings inside Files

head - View the Top of a File

tail - View the Bottom of a File

sort - Print a File in Sorted Order

Class Exercise 5

Class Exercise

Class Quiz

`pwd` - Show Your Current Directory

`cd` - Change Directory

`ls` - List the Contents of a Directory

`cat` - Print the Contents of a File

`rm` - Delete a File

`mkdir` - Create a Directory

`rmdir` - Delete a Directory

`cp` - Copy Files

`mv` - Move a File or Directory

`echo` - Print Text to the Terminal

`hostname` - Print the Name of Your Host Machine

`more`

`less`

`grep` - Finding Strings inside Files

`head` - View the Top of a File

`tail` - View the Bottom of a File

`sort` - Print a File in Sorted Order