What is the use of ‘grep’ command?
‘grep’ is a pattern search command. It searches for the
pattern, specified in the command line with appropriate
option, in a file(s).
Syntax : grep
Example : grep 99mx mcafile
What is the difference between cat and more command?
Cat displays file contents. If the file is large the
contents scroll off the screen before we view it. So
command 'more' is like a pager which displays the
contents page by page.
Write a command to kill the last background job?
Which command is used to delete all files in the current
directory and all its sub-directories?
rm -r *
Write a command to display a file’s contents in various
$od -cbd file_name
c - character, b - binary (octal), d-decimal, od=Octal
What will the following command do?
$ echo *
It is similar to 'ls' command and displays all the files
in the current directory.
Is it possible to create new a file system in UNIX?
Yes, ‘mkfs’ is used to create a new file system.
Is it possible to restrict incoming message?
Yes, using the ‘mesg’ command.
What is the use of the command "ls -x chapter[1-5]"
ls stands for list; so it displays the list of the files
that starts with 'chapter' with suffix '1' to '5',
chapter1, chapter2, and so on.
Is ‘du’ a command? If so, what is its use?
Yes, it stands for ‘disk usage’. With the help of this
command you can find the disk capacity and free space of
Is it possible to count number char, line in a file; if
Yes, wc-stands for word count.
wc -c for counting number of characters in a file.
wc -l for counting lines in a file.
Name the data structure used to maintain file
‘inode’, each file has a separate inode and a unique
How many prompts are available in a UNIX system?
Two prompts, PS1 (Primary Prompt), PS2 (Secondary
How does the kernel differentiate device files and
Kernel checks 'type' field in the file's inode
How to switch to a super user status to gain privileges?
Use ‘su’ command. The system asks for password and when
valid entry is made the user gains super user (admin)
What are shell variables?
Shell variables are special variables, a name-value pair
created and maintained by the shell.
Example: PATH, HOME, MAIL and TERM
What is redirection?
Directing the flow of data to the file or from the file
for input or output.
Example : ls > wc
How to terminate a process which is running and the
specialty on command kill 0?
With the help of kill command we can terminate the
Syntax: kill pid
Kill 0 - kills all processes in your system except the
What is a pipe and give an example?
A pipe is two or more commands separated by pipe char
'|'. That tells the shell to arrange for the output of
the preceding command to be passed as input to the
Example : ls -l | pr
The output for a command ls is the standard input of pr.
When a sequence of commands are combined using pipe,
then it is called pipeline.
Explain kill() and its possible return values.
There are four possible results from this call:
‘kill()’ returns 0. This implies that a process exists
with the given PID, and the system would allow you to
send signals to it. It is system-dependent whether the
process could be a zombie.
‘kill()’ returns -1, ‘errno == ESRCH’ either no process
exists with the given PID, or security enhancements are
causing the system to deny its existence. (On some
systems, the process could be a zombie.)
‘kill()’ returns -1, ‘errno == EPERM’ the system would
not allow you to kill the specified process. This means
that either the process exists (again, it could be a
zombie) or draconian security enhancements are present
(e.g. your process is not allowed to send signals to
‘kill()’ returns -1, with some other value of ‘errno’
you are in trouble! The most-used technique is to assume
that success or failure with ‘EPERM’ implies that the
process exists, and any other error implies that it
An alternative exists, if you are writing specifically
for a system (or all those systems) that provide a
‘/proc’ filesystem: checking for the existence of
‘/proc/PID’ may work.