Print("Please enter a string "); $input_string = <STDIN>; chop($input_string); $rev_string = reverse($input_string); if($input_string eq $rev_string){ print("The string is a palindrome"); }else{ print("The string is NOT a palindrome"... Read More

Step 1. Set environemen variable EDITOR=vi if not set Step 2. Give command crontab -e Step 3. Add following entry at the end 0 4 * * * <Your command to run at 4:00 am morning> Read More

kill 0 Read More

ps -eaf|cut -d f2|tr -s " "|kill Read More

echo $string | cut -d" " -f1 echo $string | cut -d" " -f2 echo $string | cut -d" " -f3 Read More

echo $SHELL Read More

Virtual memory like as a temparary storage area.It consists of page table.In this pages are divided into frames.It is a contingous memroy allocation.It is also called logical memory. Read More

A process is a collection of virtual memory space, code, data, and system resources. A thread is code that is to be serially executed within a process. A processor executes threads, not processes, so each application has at least one process, and a... Read More

Suppose you are using db2 and ksh ---------------------------- #!/usr/bin/ksh connect to <Serve Name>:<Port NO>@<Instance Name> user <USERID> using <Passwd> ----------------------------------- If u have profile and... Read More

export LANG=C will make the variable LANG the global variable, put it into the global environment. all other processes can use it. LANG=C will change the value only in the current script. Read More

Every program whether on UNIX or Linux should end at a certain point of time and successful completion of a program is denoted by the output 0. If the program gives an output other than 0 it defines that there has been some problem with the... Read More

Will return the status of the command which is executed lastly. 0 => Success 2 => Error $? ---> will give the exit status of last background process ZERO for sucess. NON-ZERO for unsuccess Read More

pwd Read More

wc Read More

grep -r string * Read More

if {condition} then ? fi Read More

- -eq, -ne, -lt, -le, -gt, -ge Read More

Echo command is used to display the value of a variable. There are many different options give different outputs such as usage c suppress a trailing line, returns a carriage line, -e enables interpretation, returns the carriage. Read More

Login shell is very useful as it creates an environment which is very useful to create the default parameters. It consists of two files they are profile files and shell rc files. These files initialize the login and non login files. Environment... Read More

Shebang is nothing but a # sign followed by an exclamation. This is visible at the top of the script and it is immediately followed by an exclamation. To avoid repetitive work each time developers use shebang. After assigning the shebang work we pass... Read More

This line is called as "Hash Bang" Statement. This tells the OS that the particular needs the respective shell for execution. If a script file has this hash bang statement along with execution permission, then this file can be run directly without... Read More

For C shell , first /etc/.login script is run & after that ~/.login is run & then ~/.cshrc is run. Read More

This utility is use to cut out columns from a table or fields from each line of a file. cut can be used as a filter. Either the -b, -c, or -f option must be specified. -b list The list following -b specifies byte positions (for instance, -b1... Read More

The Bourne shell (sh) , The C shell (csh) , The Korn shell (ksh) , The Z-Shell (zsh) , The POSIX shell, The Bourne Again SHell (Bash)null Read More

Preemptive multitask Read More

grep "^[ ]*$" filename.txt In character set (between [ and ] one space and tab is given) this command will gives all the blank line including those having space and tabs (if pressed)only Read More

whoami Read More

1. Mutexes can synchronize threads within the same process or in other processes. 2. Mutexes can be used to synchronize threads between processes if the mutexes are allocated in writable memory and shared among the ... Read More

date Read More

who Read More

rm Read More

rm -rf Read More

mail Read More

mail somebody@techinterviews.com -s ?Your subject? -c ?cc@techinterviews.com? Read More

grep string filename Read More

grep string * Read More

They are process IDs given to processes. A PID can vary from 0 to 65535. Read More

ps Read More

kill pid Read More

ps -ag Read More

./process-name & Read More

$1, $2 and so on. $0 is your script name. Read More

Shell scripting is used to program command line of an operating system. Shell Scripting is also used to program the shell which is the base for any operating system. Shell scripts often refer to programming UNIX. Shell scripting is mostly used to... Read More

- -s filename tells you if the file is not empty, -f filename tells you whether the argument is a file, and not a directory, -d filename tests if the argument is a directory, and not a file, -w filename tests for writeability, -r filename tests for... Read More

There are many advantages of shell scripting some of them are, one can develop their own operating system with relevant features best suited to their organization than to rely on costly operating systems. Software applications can be designed... Read More

- ! tests for logical not, -a tests for logical and, and -o tests for logical or. Read More

$# Read More

if {condition} then {statement} elif {condition} {statement} fi Read More

There are many disadvantages of shell scripting they are * Design flaws can destroy the entire process and could prove a costly error. * Typing errors during the creation can delete the entire data as well as partition data. * Initially process is... Read More

or {variable name} in {list} do {statement} done Read More

Major disadvantage of using shell scripting is slow execution of the scripts. This is because for every command a new process needs to be started. This slow down can be resolved by using pipeline and filter commands. A complex script takes much... Read More

while {condition} do {statement} done Read More

There are many situations where typing errors can prove to be a real costly effort. For example a single extra space can convert the functionality of the program from deleting the sub directories to files deletion. cp, cn, cd all resemble the same... Read More

case {variable} in {possible-value-1}) {statement};; {possible-value-2}) {statement};; esac Read More

Question : For class I need to create the command line. cAN ANYONE HELP ME? Using the commands ps, cut, tr and kill, along with pipes, write a command that will find all sleep processes running on the system and kill them. ... Read More

read {variable-name} Read More

Variables can be defined by the programmer or developer they specify the location of a particular variable in the memory. There are two types of shells they are Systemvariables and user defined variables. System variables are defined by the system... Read More

Graphical user interface provided the much needed thrust for controlling a computer and its applications. This form of language simplified repetitive actions. Support for different applications mostly depends upon the operating system. These... Read More

function-name() { #some code here return } Read More

The parameters to your script can be passed as -n 15 -x 20. Inside the script, you can iterate through the getopts array as while getopts n:x option, and the variable $option contains the value of the entered option. Read More

These are known as standard input, output and error. These are categorized as 0, 1 and 2. Each of these functions has a particular role and should accordingly functions for efficient output. Any mismatch among these three could result in a major... Read More

Sourcing commands help you to execute the scripts within the scripts. For example sh command makes your program to run as a separate shell. .command makes your program to run within the shell. This is an important command for beginners and for... Read More

The non login shell files are initialized at the start and they are made to run to set up variables. Parameters and path can be set etc are some important functions. These files can be changed and also your own environment can be set. These functions... Read More

Environment variables are set at the login time and every shell that starts from this shell gets a copy of the variable. When we export the variable it changes from an shell variable to an environment variable and thesevariables are initiated at the... Read More

Code in the script (Shell is interprted) as shell is a interpreter where as editor is not inter preter certain set of commands(predefined) are used to handle editor Read More

The inode is the focus of all file activity in the file system. There is a unique inode allocated for each active file, each current directory, each mounted-on file, text file, and the root. An inode is "named" by its device/i-number pair. Read More

$# means, number of positional parameters set Read More

$1: the 1st parameter $2: the 2nd parameter ... $* All parameters in the command line Read More

vi filename e.g vi abc.txt but you cannot write to it easy way if file is small cat filename and contents is display on screen Read More

Broadly categorised in 3 for while until Read More

Shell script accepts parameters in following format... $1 : first $2 : second....so on upto $9 : 9th param whereas $0 : gives script/function name If your script has more than 9 params then accept in following way... ${12} : 12th param ${18} ... Read More

cat filename.txt | cut -c 10-20 Read More

sed -n '25p' filename.txt Read More

vi file name then go to command mode %s/n/xyz/g Read More