Python scripts vs Bash scripts in Linux

Almost all Linux users who are at least familiar with bash shell commands will be at home in writing simple bash scripts to automate tasks. For those who do not know how to write a bash script, here is how you do it.

Open a new file in your favorite text editor and save it in any name of your choice but with the extension .sh. For example, let us name it 'myfirstscript.sh' . The 'sh' file extension is not mandatory but is a nice way for us to later remember that this file is a script.

Now in this file (myfirstscript.sh), enter the following line.

#!/usr/bin/bash

This line should always be entered the first thing in any bash script you create. It lets the shell know where to find the bash program. In some Linux distributions the bash command is located at /bin/bash. When in doubt, use the 'which' command to find the location as follows :

$ which bash
/usr/bin/bash

# Continuation of the above script ...
# Now lets enter a few commands in this script ...
ls -l
sleep 2
who
sleep 2
w

Nothing spectacular here. Note that 'sleep' is used to pause the execution process for certain time in seconds. Next fire up a console (xterm, gnome-terminal ...) and set the executable bit for the script myfirstscript.sh as follows :

$ chmod u+x myfirstscript.sh

This lets you execute the script by its name as follows :

$ ./myfirstscript.sh

All this may seem easy. But you can get added benefits if you substitute 'bash' with Python language to write your scripts. Noah Gift provides compelling reasons to pick up Python programming language skills and start writing your scripts in this language. If you do not know Python language and is looking for some direction then you should look at the two books Core Python programming and Python phrasebook which will give you a head start in mastering this powerful but easy to learn language.

Make your bash scripts user friendly using - dialog

If you have installed Linux using the text installer, then you will find a neat professional looking install process. You can rest assured that no extreme programming has gone into creating the text installer. In fact, it has been created using a utility called dialog. Dialog is a utility installed by default on all major Linux distributions. It is used to create professional looking dialog boxes from within shell scripts.

Some of the dialogs supported are Input boxes, Menu, checklist boxes, yes/no boxes, message boxes, radiolist boxes and text boxes.

Creating a dialog is very easy. Here I will explain how to create dialog boxes of different types.

Input boxes : These allows the user to enter a string. After the user enters the data, it is written to standard error . You may also redirect the output to a file.

$ dialog --title "Ravi's Input Box" 
    --inputbox "Enter the parameters..." 
    8 40

As you can see, the options are self explanatory. The last two options 8 and 40 are the height and width of the box respectively.

Fig: Inputbox

Textbox : This is a box which takes a file as the parameter and shows the file in a scrollable box.

$ dialog --title "textbox" --textbox ./myfile.txt 22 70 

... it shows the file myfile.txt in a textbox.

Fig: Textbox showing the file.

Checklist : The user is presented with a list of choices and can toggle each one on or off individually using the space bar.

$ dialog --checklist "Choose your favorite distribution:" 
         10 40 3 
         1 RedHat on 
         2 "Ubuntu Linux" off 
         3 Slackware off

... here, 10 is the height of the box, 40 - width, 3 is the number of choices, and the rest are the choices numbered 1,2 and 3.

Radiolist: It displays a list containing radio buttons. And the user can only choose one option from the set of options.

$ dialog --backtitle "Processor Selection" 
         --radiolist "Select Processor type:" 
         10 40 4 
         1 Pentium off 
         2 Athlon on 
         3 Celeron off 
         4 Cyrix off

10 and 40 are the height and width respectively. 4 denotes the number of items in the list.

Infobox: This is useful for displaying a message while an operation is going on. For example, see the code below:

$ dialog --title "Memory Results" 
         --infobox "`echo ;vmstat;echo ;echo ;free`"
         15 85

Fig: Information box - listing the vmstat and free listing.

Fig: Message box

Dialog is usually used inside a script which gives the script a degree of user friendliness. There is another package called Xdialog which gives the same features for scripts executed in X Windows. Xdialog utility also has additional functionality not found in the dialog utility.
To know more about the dialog utility check the man page of dialog.