UNIX is a Operating System which was developed by Bell labs in between 1960-1970's. Basically it was derived from AT&T Unix in Bell Lab's. It is most popular OS in IT world that has continuous enhancement and upgrades since its invention. It is the operating system for multi tasking, multi user with high throughput in production servers in application software. UNIX is case sensitive. So our shell scripts are also case sensitive.
UNIX Special Characters
All the following characters have a special meaning or function. It they are used in a way that their special meaning is not needed, they must be escaped. To escape or remove its special function, the character must be immediately preceded with a backslash \, or enclosed with in ' ' forward tic marks (single quotes).
\ / ; , . ~ # $ & ? * ( ) [ ] ' ' " + - ! ^ = | < >
What is UNIX Shell ?
A shell is an environment or utility in Unix in which we can run our commands, programs and shell scripts (programming). In Unix, we have multiple type or flavors of shells just like different flavors of operating systems. In each flavor of shell in UNIX, it has its own set of defined commands and functions.
There are basic three types of shell used on UNIX as below :
1. Bourne 2. Bash 3. Korn
There are basic three types of shell used on UNIX as below :
1. Bourne 2. Bash 3. Korn
Shells are located in Unix either in /usr/bin directory or the /bin/ directory, it depends on the UNIX flavor and specific version with vendor/provider.
| SHELL | DIRECTORY |
| Bourne | /bin/sh OR /usr/bin/sh |
| Bash | /bin/bash OR /usr/bin/bash |
| Korn | /bin/ksh OR /usr/bin/ksh |
Shell Script
Just as the name depicts, Shell script is a script run on UNIX shell and has the list of commands that are set in a order of execution to get desired result or do calculations. By Unix shell script we can do programming where we can use conditional tests, commands, comments, store data and variable operations.
Shell scripts are ASCII text that is read by shell command interpreter that means they are not compiled. In Unix we have two type of scripts one is shell script as text and another one is functions. both are interpreted as ASCII text.
By saying it is interpreted only means, when we execute a shell script or function, a command interpreter goes through the ASCII text line by line, loop by loop, test by test and executes each statement as each line is reached from the top to the bottom.
You may navigate from here to any of topic on Unix & Linux servers. __________________________________________________________________________
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