#!/bin/bash
  while true 
  do 
    tput sc
    tput cup 0 60
    echo -en `date +"%H:%M:%S %F"`
    tput rc
    sleep 1
  done

The script saves the current cursor position with an ANSI escape sequence instruction. Then, using the tput command, the cursor is sent to row 0 (the top of the screen) and the last column minus 19 characters (19 is the length of HH:MM:SS YYYY-MM-DD). The formatted date command is displayed in green inverted color. The cursor is then sent back to its original position with another ANSI sequence that restores the original saved position.

 #!/bin/bash

 bash
 cd
 sleep
 echo
 date
 tar
 wait
 ls
 wc

 cd /

One of the most powerful standard programs available in UNIX is the shell. The shell is a program that provides you with a consistent and easy-to-use environment for executing programs in UNIX. If you have ever used a UNIX system, you have interacted with the shell.

The main responsibility of the shell is to read the commands you type and then ask the UNIX kernel to perform these commands. In addition to this, the shell provides sophisticated programming constructs that enable you to make decisions, repeatedly execute commands, create functions, and store values in variables.

This book concentrates on the standard UNIX shell called the Bourne shell.

A working knowledge of shell scripting is vital if someone wants to become good at system administration tasks. Since this tutorial tackles topics that assume a basic understanding of shell scripting, we strongly urge you to take a look at our Shell Scripting: The Basics article first…

One important aspect of shell scripting is file-oriented utility. A file-oriented utility is basically used as a filter in a pipe.

We can add a ‘-’ to get a more useful result. That is, when we have ‘file -’, the shell waits for the user input and analyses it.

Shell programming is heavily dependent on string processing. The term string is used generically to refer to any sequence of characters; typical examples of strings might be a line of input or a single argument to a command. Users enter responses to prompts, file names are generated, and commands produce output. Recurring throughout this is the need to determine whether a given string conforms to a given pattern; this process is called pattern matching. The shell has a fair amount of built-in pattern matching functionality.

This document assumes that you already have some basic understanding of at least one procedural programming language such as C. It does not assumes that you have very much knowledge of commands executed from the terminal, though, and thus should be readable even if you have never run the Terminal application before.

The techniques in this document are not specific to Mac OS X, although this document does note various quirks of certain command-line utilities in various operating systems. In particular, it includes information about some cases where the Mac OS X versions of command-line utilities behave differently than other commonly available versions such as the GNU equivalents commonly used in Linux and some BSD systems.

Old Unix hands already know this, but new Unix (Linux) users may be asking, ‘What is a “watchdog script”?’ Basically it is a bash or other script that is run via cron periodically to check on a persistent service. The watchdog script takes actions based on the state of the service it monitors.

In this context, a one-liner is a set of commands normally joined through a pipe (|). When joined by a pipe, the command on the left passes its output to the command on the right. Simple or complex, you can get useful results from a single line at the bash command prompt.

For many years, I've wanted a simple command-line timer program to use in conjunction with short human tasks — the sort of thing my wristwatch timer works for, but I'm not always wearing that watch. I want something that provides some indication of elapsed time or time remaining. Amazingly, the commercial Unixes I'm familiar with do not provide such a utility; nor does one seem to be readily available with the standard X Window tools.

If you've worked in Unix for any length of time, you're probably familiar with psg or some such variant. Psg stands for "ps through grep" (essentially a ps query whose result is piped grep). It works and works well, but sometimes you need more than just a process string; sometimes you want the process string AND the process ID (PID) — separated. Oh yes, and since we're compiling a wish list here, how about the operation simply telling me how many processes match a given target string. I'll show how to do all of that — and do it without having to run multiple ps commands and filtering those results through several piped operations.

The awk utility is a small program that executes awk language scripts, which are often one-liners, but just as easily may be larger programs saved in a text file. For example, to execute an awk script saved in the file prg1.awk and have it process the file data1, you could use a command such as:

The first way is the more modern way, and is really the only way that you want to use. You surround the command that you want to substitute with parentheses, and then precede it with a dollar-sign. Here, we’re using echo to show the output of date.

echo $(date)

Conditions are elements that you will use often. With conditions you will test for an element and then create a response to the results of that test. In most situations, conditions will be a very important part of your scripts.

$ cat arraymanip.sh
#! /bin/bash
Unix[0]='Debian'
Unix[1]='Red hat'
Unix[2]='Ubuntu'
Unix[3]='Suse'

echo ${Unix[1]}

$./arraymanip.sh
Red hat

Kommander is a simplified and modified version of Qt Designer which lets you add scripting abilities to the dialogues it makes. It saves the result as a designer UI file which can be run with Kommander Executer. It is the easiest way to make simple programmes, I like to think of it as graphical shell scripting.

Konstuct is a program to download and install KDE from sources. This tutorial takes us through using Kommander to make a graphical program to configure and run Konstruct.

In C, defines strcat(3), strcpy(3), strlen(3), and strcmp(3) for string concatenation, copy, size, and test operations respectively. Such basic operations are needed constantly when programming in any language, and shell scripting is no exception.

Uses a simple text file of paths and filenames for input -- so you can save the results of "find" to a file, run rezip, and the files will be re-compressed one at a time, with a running log and no user intervention (as long as there's free space on the destination drive.) Example:

$ find /mnt/bkps -name *.gz > ~/rezipp-files.txt && rezip

Among the many interesting things that I saw, two stand out: Eclipse and the scripting language called Groovy. I already have written about Eclipse, so here I simply note that Eclipse now seems to dominate the Java IDE world. Groovy, on the other hand, is new. It prompted me to look at Python-like scripting languages that run in a Java environment.

In this article, I discuss Jython and Groovy, two scripting languages that use the Java runtime environment. By the way, JavaScript has nothing to do with the Java language, so it is not considered here.