Unix Basic Commands

Day 2
Unix Fundamental &
Name of
Commands
presentation
Ananthi Murugesan
• Company name

Module 1

Module 1
Unix Basic Commands

www.ananthim.wordpress.com

Author :- Ananthi Murugesan

2

The Online Manual
Syntax:
man –[k|X] keyword

in which X is the number of one of the
manual sections
Examples:
$ man ls
Display the “ls" man page.
$ man -k cat Display entries with keyword "cat".
$ man passwd Display the "passwd" man page-Section 1.
$ man 4 passwd Display the "passwd" man page-Section 4.



Getting help about commands
The Unix manual, usually called man pages, is available on-line
to explain the usage of the Unix system and commands.
How to use
Syntax:
man [options] command_name
Common Options
-k keyword list command synopsis line for all keyword
matches
-M path path to man pages
-a show all matching man pages (SVR4)
info command_name - help for the internal commands
help -– command_name– gives command synatx



Id command

Syntax:
id
Displays effective user and
group identification for session

Example:
$id
uid =303 (user3) gid=300 (class)



Who & whoami
Syntax:
who

Reports information about users who are
currently logged on to a system

Examples:
$ who
root
tty1p5 Jul 01 08:01
user11 tty1p4 Jul 01 09:59
$ who am i
$ whoami
user12


The cal command

Syntax:
cal Reports the calendar of 2005 September(Current
month)

Example:
$ cal 8 2005 for Aug 2005
$ cal 2005 for the full calendar of year 2005



The Finger command
Finger: Displays information about the users
currently logged on

Eg:
$ finger user1

Login name: user1
Directory: /export/home/user1 shell:/usr/bin/sh
On since Sep 05 09:10:12 on tty1
No plan



The password Command

Syntax:
passwd Assigns a login password

Example:
$ passwd
Changing password for user1
Old password:
New password:
Re-enter new password:



9

The clear Command

Syntax:
clear

Clears terminal
screen



10

What Is a File System?
Collection of control structures and Data blocks that occupy
the space defined by a partition and allow for the storage
and management of data.



12

File Types
Common File Types
Ordinary files: regular files

Directory files: table of contents, that stores a list of
files/directories within that directory
Device files: For every device there is a device file used by
kernel to interact with the device.
Symbolic Link: Its link to other files



13

Ordinary Files

A regular file simply holds data.
Regular files can hold ASCII text, binary data, image data,
databases, application-related data, and more.



14

Directory Files

Directory
name inum
d1 4
f1 10

Inode Table
# type mode links user group
4 dir 755 2
user1 group1
10 file 644 1
user1 group1


date
Sep 5 9:30
Sep 5 9:45

size
512
12


loc

15

Symbolic Links
contains the path of the file to which it links
Exists even after the source file is removed and is exactly
similar to Windows shortcut

Syntax: ln –s sourcefile linkfile
Eg: ln -s /f1 f1.lnk

Overcomes 2 limitations of Hard Link:
1. possible across filesystems
2. can link to a directory



16

Device files

A device file provides access to a device.

# cd /devices/pci@1f,0/pci@1,1/ide@3
# ls -l
brw------- 1 root sys 136, 0 Apr 3 11:11 dad@0,0:a
Two types of device files:
block device files
character device file



17

Listing the directory contents

ls
Syntax
ls [options] [file….]
Options
-l
list in long format
-a
list all file including those
beginning with a dot
-i
list node no of file in first column
-s
reports disk blocks occupied by file
-R
recursively list all sub
-F
mark type of each file
-C
display files in columns



Meta characters
• 0 or more characters
?

1 character

[-]

matches any one character between the brackets

[^ ]

not matches any one character in the brackets



Module 3
Managing Files


20

Files & Directories - Objectives

File Permissions
Directory Related Commands
File Related Commands

Introduction to editors



File access permissions

• Refers to the permissions associated with a
file with respect to the following
• Permission Levels
– User (owner) (u)
– Group (wheel, staff, daemon, etc.) (g)
– World (guest, anonymous and all other
users) (o)


Permission settings

Permission Settings



Changing permissions - chmod
chmod u+x file_name
Syntax:

chmod <category> <operation> <permission>
<filename(s)>
Or
chmod <octal number> filename
Eg - chmod 755 result.txt
Octal Number
Read(r) = 4
Write(W) = 2
Execute (X) = 1


$ ls –l
-rwxr-xr-x
-rwxr-xr-x
drwxr-xr-x
-rwxr--r-x

1user1 training
3 user1 faculty
3 user1 faculty
3 user1 faculty

12373 Dec 15 14:45 a.out
4096 Dec 15 11:56 awkpro
4096 Dec 15 11:56 test
4096 Dec 15 11:56 latest

Owner Groups

Others

File Type


Meaning

-

Ordinary File

D

Directory File

C

Character
Special File

B

Block Special
File

L

drwxr-xr-x

File Type

Symbolic special
File


Changing permissions - Calculation

In case we need to set the full access for the owner and read
and Execute for the user for the groups and other
Here is the calculation
( read = 4 )+( Write = 3 )+( Execute = 1 ) - 7

So to change the file permission we need to set the chmod
value as 755
Eg , chmod 755 result.txt



Directory creation

Command Syntax
mkdir [OPTION] DIRECTORY
$mkdir <path>/<directory>
$mkdir –m <directory>
$mkdir –p <directory1>/<directory2>/<directory3>
Example:
◦mkdir project1
This creates a directory project1 under current directory
Note:
Write and execute permissions are needed for the user to
create a directory


Directory Removal

rmdir command removes directory
Syntax
– rmdir <directory name>
Example
Removes project1 directory in the current directory
rmdir project1
Remove multiple directories
rmdir pos1 pos2
Remove the directory recursively
rmdir –p dir1/dir2/dir2
Rule: rmdir can be executed to a directory if it is empty and
not the current directory


File Related Commands
File operation

Commands

Copying File

cp

Moving a file

mv

Removing a file

rm

Displaying a file

cat

Prints the first few line of the file

head

Prints the last few line of the file

tail

Display the file at one successful screen

more

Cut out the selected fields of each line of a file

Cut

Merge lined of the file

paste



Commands - cp
Used to copy files across directories
Syntax
cp <source file> <new file name>
Example
cp file1 file2
Note:
cp -r /dev/tty myfile
-r
Recursive copy; copy subdirectories under the
directory if any
-f
force



Commands – rm

Used to remove a file
Syntax
rm file



Commands – cat
Reads one or more files and prints them to the standard
output
Syntax
cat <redirection operator> <file name>
EX: cat filename.txt Displays the file content
-n -> print the line numbers
-b -> no number for non empty lines
-s -> suppress the repeated blank lines
Operators:
> - overwrite existing content of file
>> - appends the content with new content


Commands – head/tail
head:
-n -> n lines from top
head -23 file -> 23 lines from top
head –n -23 -> prints total – 23 lines i.e., prints all lines
except 23 lines from end of file.
-c 23 -> prints 23 bytes from top
tail:
-c 23 -> prints 23 bytes from bottom
-n -> n lines from bottom
-n +23 -> prints from 23rd line to till end
-n -23 -> prints 23 lines from last(reverse direction count)
head -23 file | tail -5 -> prints 5 lines from 23 lines



Commands – more/less
More:
More is a filter for paging through text one
screenful at a time.

EX: more filename
less:
Opposite of more
Less is a program similar to more (1), but which allows
backward movement in the file as well as forward
movement. Also, less does not have to read the entire
input file before starting, so with large input files it starts
up faster than text editors like vi.
EX: less filename.txt


cut command

Used to cut fields from each line of a file or columns of a table
cut –d: -f1,5 /etc/passwd
cut –c2 test
second character of each line
cut –c-2 test
first 2 characters of each line



35

Unix - Stop and Think

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Unix Basic Commands

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