Basics of UNIX Commands

BASICS OF UNIX
COMMANDS
Prepared By:- Subra Kumar Das
Designation: Operations Support
Analyst
Version 1.0

1. Introduction to Unix
2. What is File & Directory ?
3. Pathnames
4. Listing files and directories
5. Making Directories
6. Changing to a different directory
7. Copying Files and directories
8. Moving Files and directories
9. Removing files and directories
10.Creating a file using vi editor
11.Displaying the contents of a file on the screen
12.Searching the contents of a file
13.Redirecting the Output
14.Redirecting the Input
15.Pipes
16.Wildcards
Agenda

Go back to Agenda
• UNIX Operating system originally developed in 1969 by a group of AT&T
employees at Bell Labs.
• Various flavours of Unix & Unix-like OSes are Solaris, Linux etc.
• Designed to be portable, multi-tasking & multi-user in a time-sharing
configuration.
• Unix systems are characterized by various concepts:
– Use of plain text for storing data.
– A hierarchical file system.
– Treating almost everything as files.
– Use of a large number of small programs that can be strung together, as
opposed to using a single program that has the same functionality.
• Unix Philosophy :-
“Write programs that do one thing and do it well.
Write programs to work together. Write programs to handle text
streams, because that is a universal interface.”
History of UNIX

Go back to Agenda
Files: Everything in Unix is a file!!
Directories:
A directory is a file that contains directory entries.
• Each directory entry contains a file name along with a structure of
information describing the attributes of the file.
– Type of the file (normal file/directory/device file/soft link/hard link etc.)
– Size of the file
– Owner of the file
– Permissions for the file (whether other users may access this file)
– Time stamps (when the file was last modified/accessed)
• Can be considered as a container for files.
• When we first login, our current working directory is our home directory.
• Our home directory has the same name as our user-name.
File & Directory in UNIX

Go back to Agenda
There are two special directories called (.) and (..)
The current directory (.)
In UNIX, (.) means the current directory, so typing
$ cd .
means stay where we are.
The parent directory (..)
(..) means the parent of the current directory, so typing
$ cd ..
will take us one directory up the hierarchy.
Note: typing cd with no argument always returns us to our home directory.
This is very useful if we are lost in the file system.
More about Directories

Go back to Agenda
~ (our home directory)
Home directories can also be referred to by the tilde ~ character.
It can be used to specify paths starting at our home directory. So typing
$ ls ~/unix_session
will list the contents of our unix_session directory, no matter where we currently are in the file system.
More about Directories

Go back to Agenda
Pathname enables us to know where we are in relation to the whole file system.
Command:
pwd
Meaning:
Present Working Directory
Description:
The pwd command prints the absolute pathname of our current working directory.
For example, to find out the absolute pathname of our home-directory,
We need to type cd to get back to our home-directory and then type
$ pwd
which means that subra (our home directory) is in the home sub-directory,
which is in the top-level root directory called " / " .
Pathnames in UNIX

Go back to Agenda
Command:
ls
Meaning:
List
Description:
The ls command ( lowercase L and lowercase S ) lists the contents of our current working directory.
$ ls
Listing files and directories

Go back to Agenda
• There may be no files visible in our directory, in which case, the UNIX prompt will be returned.
• Files beginning with a dot (.) are known as hidden files and are not listed by ls command
• To list all files in a directory including those whose names begin with a dot, we need to type
$ ls –a
Where –a is an option and means all
• To list contents in a directory other than the present working directory, we need to type
$ ls < path to directory >
Listing files and directories

Go back to Agenda
Command:
mkdir <directory or path>
Meaning:
Make Directory
Description:
The mkdir command creates new sub-directory within the current working directory.
$ mkdir unix_session
To cross-verify if the directory has been created or not, we can type ls command,
which will show the new sub-directory named unix_session within the current working directory
Making directories

Changing to a different directory

Go back to Agenda
Command:
cd <directory or path>
Meaning:
Change Directory
Description:
The cd command changes working directory to a different directory specified with the command.
$ cd unix_session
To cross-verify if the directory has been created or not, we can type ls command,
which will show the new sub-directory named unix_session within the current working directory
Changing to a different directory

Go back to Agenda
Command:
cp < source_path > < destination_path >
Meaning:
Copy
Description:
The cp command copies files/directories from source path to destination path.
To copy files:
$ cp /home/subra/abc.txt /home/subra/unix_session/
To cross-verify if the file abc.txt has been copied or not, we can type ls /home/subra/unix_session/,
which will show the new file named abc.txt within the destination directory.
Copying File in UNIX

Go back to Agenda
To copy directory:
$ cp -r /home/subra/unix_session/ver1/ /home/subra/ver1
Where –r means recursive
To cross-verify if the directory has been copied to /home/subra or not,
we can type ls /home/subra/
which will show the directory named ver1 within the destination path.
Copying Directory in UNIX

Go back to Agenda
Command:
mv < source_path > < destination_path >
Meaning:
Move
Description:
The mv command moves files/directories from source path to destination path.
To move files:
$ mv /home/subra/unix_session/abc.txt /home/subra/abc.txt
To cross-verify if the file abc.txt has been moved or not, we can type ls /home/subra/unix_session/,
which will not contain abc.txt.
Moving File in UNIX

Go back to Agenda
To move directory:
$ mv /home/subra/unix_session/ver1/ /home/subra/ver1
To cross-verify if the directory has been moved to /home/subra or not,
we can type ls /home/subra/
which will show the directory named ver1 within the destination path.
Moving Directory in UNIX

Go back to Agenda
Command to remove a file:
rm < file_path >
Meaning:
Remove
Description:
The rm command removes (deletes) file from the file path.
Command to remove a directory:
rmdir < directory_path >
Meaning:
Remove Directory
Description:
The rmdir command removes (deletes) directory from the directory path.
We need to make sure directory which we need to remove is empty, as UNIX will not let us remove
a non-empty directory with rmdir.
Removing File & Directory in UNIX

Go back to Agenda
Command to remove a non-empty directory:
rm –r < file_path >
Meaning:
Remove everything recursively
Description:
The rm command removes (deletes) all files and directories in the directory named in the command.
However, it would also present a prompt for approval to delete each of the files.
Command to remove a non-empty directory without receiving a prompt for each file :
rm -rf < directory_path >
Meaning:
Remove everything recursively and forcefully
Description:
The rmdir command removes (deletes) directory from the directory path.
Removing non-empty Directory in UNIX

Creating a file using vi editor

Go back to Agenda
To create a file called unix_file containing a list of statements, we need to type
$ vi unix_file.txt
Then type in the names of some OS. Press [Return] after each one.
Zero is a number.
A is a Capital Letter Alphabet
b is a small letter Alphabet.
zero is also a number
Apple is fruit
UNIX is OS
WIN is OS
^D {this means press [Ctrl] and [d] to stop}
Type:
:wq
Where w means write (save) and q means quit.
Creating a file using vi editor

Displaying contents of a file on screen

Go back to Agenda
clear (clear screen)
Before we start the next section, we may like to clear the terminal window of the previous commands
so the output of the following commands can be clearly understood.
At the prompt, we need to type
$ clear
This will clear all text and leave us with the $ prompt at the top of the window.
cat (concatenate)
The command cat can be used to display the contents of a file on the screen.
Type:
$ cat unix_file.txt
If the file is longer than the size of the window, so it scrolls past making it unreadable.

Go back to Agenda
less
The command less writes the contents of a file onto the screen a page at a time.
Type
$ less unix_file.txt
We can press the [space-bar] if we want to see another page, and type [q] if we want to quit reading.
As we can see, less is used in preference to cat for long files.

Go back to Agenda
head
The head command writes the first n no. of lines of a file to the screen.
Then we need to type
$ head -5 unix_file.txt
Which will print first 5 lines of a file named unix_file.txt
tail
The tail command writes the last n no. of lines of a file to the screen.
we need to type
$ tail -5 unix_file.txt
Which will print last 5 lines of a file named unix_file.txt

Searching the contents of a file

Go back to Agenda
grep
It searches files for specified words or patterns.
We can type
$ grep zero unix_file.txt
grep will print out each line containing the word zero in a file named unix_file.txt
We can try typing
$ grep Zero unix_file.txt
In this case, grep will print out each line containing the word Zero in a file named
unix_file.txt
The grep command is case sensitive; it distinguishes between Zero and zero.
To ignore upper/lower case distinctions, we can use the -i option, i.e.
$ grep -i zero unix_file.txt

Go back to Agenda
To search for a phrase or pattern, we must enclose it in single quotes (the apostrophe
symbol).
For example to search for spinning top, type
$ grep -i ‘numeric zero' unix_file.txt
Some of the other options of grep are:
-v display those lines that do NOT match
-n precede each matching line with the line number
Don't forget, we can use more than one option at a time.
For example, the number of lines without the words zero or Zero is
$ grep -iv science science.txt

Go back to Agenda
We use the > symbol to redirect the output of a command.
$ echo startoffile > unix_file_new.txt
Above command will create a new file with a name unix_file_new.txt and startoffile as a
content in the first line.
The symbol >> appends standard output to a file. So to add more items to the file
unix_file.txt, we need to type
$ echo Mango is a fruit >> unix_file.txt
Which will add Mango is a fruit to a file named unix_file.txt
After execution of above command, we can type cat command followed by the filename /
filepath to verify the same.
Redirecting the Output

Go back to Agenda
We use the < symbol to redirect the input of a command.
The command sort alphabetically or numerically sorts a list.
To sort the list and output to the screen
$ sort < unix_file.txt
Which will sort the list alphabetically for the start letter.
Note: Capital Letter will be higher in the order always then the small letter.
To output the sorted list to a file
$ sort < unix_file.txt > sorted_unix_file.txt
Redirecting the Input

Go back to Agenda
What we really want to do is connect the output of the cat command directly to the input
of the grep command.
This is exactly what pipes do.
The symbol for a pipe is the vertical bar |
For example, by typing
$ cat unix_file.txt
$ grep zero unix_file.txt >> unix_file_zero.txt
We get a new file named unix_file_zero.txt with all the lines having zero in it.
Now
$ cat unix_file.txt | grep zero >> unix_file_zero.txt
will give the same result as above, but it is quicker and cleaner as it takes less number of
lines.
Pipes

Go back to Agenda
The * wildcard
The character * is called a wildcard, and will match against none or more character(s) in
a file (or directory) name.
For example, in our unixstuff directory,
$ ls list*
This will list all files in the current directory starting with list....
By typing
$ ls *list
This will list all files in the current directory ending with ....list
Wildcards

Go back to Agenda
The ? wildcard
The character ? will match exactly one character.
By typing
$ ls ?list.txt
Will list out all the files ending with list like flist, slist, mlist but not fglist as single ? is
used
Wildcards

Go back to Agenda
The [ ] wildcard
Defines class of characters.
For range of characters – can be used.
To exclude certain character or range of characters ! Can be used.
By typing
$ ls [a-z]*.txt
Will list out all the txt files starting with a to z in lower case
$ ls [A-Z]*.txt
Will list out all the txt files starting with A to Z in upper case
Wildcards

Go back to Agenda
By typing
$ ls [0-9]*.txt
Will list out all the txt files starting with numeric 0 to 9
$ ls [!0-9]*.txt
Will list out all the txt files not starting with numeric 0 to 9
Similarly to exclude all the files starting with [a-z] and [A-Z], we can use
$ ls [!a-zA-Z]*.txt
Wildcards

Basics of UNIX Commands

Recommended

More Related Content

What's hot (20)

Similar to Basics of UNIX Commands (20)

Recently uploaded (20)

Basics of UNIX Commands