Unix Questions

What is Shell  

Shell is interface between user and kernal.

shell scripting

Shell scripting is a series of sequence of UNIX commands written in a plan txt file.

importance

Shell scripts takes input from the user file and displays it on screen, very useful to creating your own command,to automate some tasks,mainly it saves time.

$ LS, $ LS LTR

$ LS its list file of current directory, $ LS LRT shows files with long format

$ CD, $ CD test,$ CD ..

it changes directory to home directory, it chnages to test directory, it move back to parent directory

$ mkdir test

create directory

$rmdir test

remove directory

$ cp file1 test

it copies file1 to test directory

$ cp file1 file1.bak

it takes backup of file1

rm file1

remove file 1

$ mv file1 file2

it move or rename file1 to file2

$more

it checks or display one page at a time

$ cat file1

it display content of file1

$ cat test1 > test2

create a new file name teste with data of test1 file

$ find .-name '*.t' -print

it searches in the current diretory and in all sub dir for files ending with name t and writes their name in output

$ finger

user info

$date

date info

$who

list of logging user

$ grep Hello file1

it searches for the line containing hello in file1

$kill 1892

it kill process id 1892

lp

to print file

$ head -15 file1

it display first 15 lines of file1

$ tail -15 file1

it display last 15 line of file 1

type of shell

bourne shell (sh), c shell (csh), korn shell (KSH), bourne again shell (bash)

Advantage of C shell over bourne shell

C shell allows alias system and remember command history.

how many shell script come with UNIX system

280 shell scripting

by default file permission

666 rw-rw-rw-

how modify file permision

umask

variable

2 type - unix defined will be always in caps letter and user defined will be in small letters, variable store as string

unchangeable variable

$ a=10, $readonly a,

to clear variable

$ a=10, $ unset a,

$uptime

to know sine when system is up

Shebang (#!/bin/bash)

shebang is a #sign followed by an exclamation. Shebang mainly determine the location of the engine.

Unix

Unix is a multitasking multi user operating system  which was developed in 1960s by Bell System. It is not a open sourced.

Why unix better than Windows

Unix handles high server loads better than windows. Server running on UNIX enjoy extremely high up time