Notes

Writing Your First Script And Getting It To Work

To successfully write a shell script, you have to do three things:

1-Write a script .
2-Give the shell permission to execute it .
3-Put it somewhere the shell can find it .

A shell script is a file that contains ASCII text. To create a shell script, you use a text editor like vi,vim ,Emacs ,nano ,gedit

Example:
#!/bin/bash (Everything that appears after a "#" symbol is ignored by bash)
#My First script
#echo "Heelo World" (The last line is the echo command. This command simply prints its arguments on the display)

Setting Permissions :
The next thing we have to do is give the shell permission to execute your script. This is done with the chmod command

#chmod 755 hello_world

The "755" will give you read, write, and execute permission. Everybody else will get only read and execute permission. If you want your script to be private (i.e., only you can read and execute), use "700" instead.

Putting It In Your Path
At this point, your script will run. Try this:

#./hello_world

You should see "Hello World!" displayed. If you do not, see what directory you really saved your script in, go there and try again.
When you type in the name of a command, the system does not search the entire computer to find where the program is located. That would take a long time. You have noticed that you don't usually have to specify a complete path name to the program you want to run, the shell just seems to know.

Well, you are right. The shell does know. Here's how: the shell maintains a list of directories where executable files (programs) are kept, and only searches the directories in that list. If it does not find the program after searching each directory in the list, it will issue the famous command not found error message.

This list of directories is called your path. You can view the list of directories with the following command:
#echo $PATH

This will return a colon separated list of directories that will be searched if a specific path name is not given when a command is attempted. In our first attempt to execute your new script, we specified a pathname ("./") to the file.

You can add directories to your path with the following command, where directory is the name of the directory you want to add:

#export PATH=$PATH:directory

Most Linux distributions encourage a practice in which each user has a specific directory for the programs he/she personally uses. This directory is called bin and is a subdirectory of your home directory. If you do not already have one, create it with the following command:

#mkdir bin

Move your script into your new bin directory and you're all set. Now you just have to type:

#hello_world

and your script will run .