Why bash scripting

Apart from what others have said, I'd like to point out what's in my opinion the main reason to learn Bash: it's the almost standard Linux shell. Other scripting languages are surely useful, and maybe a lot more powerful, but what you'll be dealing with when you have a terminal in front of you is Job control languages and shells Main article: Shell script.

A major class of scripting languages has grown out of the automation of job control, which relates to starting and controlling the behavior of system programs. Others, such as AppleScript offer the use of English-like commands to build scripts. Python, Ruby and Perl are great, but are more general tools; in certain cases embedded devices or other minimalistic systems they can be considered bloat or in other situations they might pose a security risk for environments where you want very high security and try to eliminate any unnecessary package.

Also, bash is production proven for myriad of administrative tasks and it is easy to find scripts that will cover very complicated scenarios exceptions and handle them gracefully. Easier, probably not. I actually prefer perl to bash scripting in many cases. Bash does have one advantage, though, especially on Linux systems: it's all but guaranteed to be installed.

And if it's not, its largely-compatible father sh will be, cause almost all system scripts are written for sh. Even perl isn't that ubiquitous, and it's everyfreakingwhere. Bash and the original Bourne sh and myriad derivatives is - from one perspective - an incredibly high-level language. Where many languages use simple primitives, shell primitives are entire programs. That it might not be the best language to express your tasks, doesn't mean it is dead, dying, or even moribund.

If you do lots of GUI stuff, you'll probably only meet bash whenever you're doing some sort of customization on your own machine. Various hacks and stuff. If you use the command line to do stuff, bash is just indispensable.

In fact, being good on the command line requires bash or some other shell familiarity. I get miles out of having learned Bash when I wanted to navigate around my harddrive quickly. Writing it in bash was simple and easy. And there's lots of easily accessed, and free, stuff that'll show you how. Also, learning Bash is great for understanding how Unix and some of the core stuff really works -- and how far we've come with tools like Python.

I'm a perl guy, but the number of the bash or ksh functions I use and create on a daily basis is quite significant. Again, especially for environment variables nothing beats shell, and quite a few programs use environment variables.

In Perl, I have to write a bash alias or function that calls the Perl script, which writes out a temporary bash script, which then gets sourced after Perl exits in order to make the change in the same environment I'm launching from.

I've done this, especially for heavy-lifting on path variables. But there's no way to do it in just Perl or python or ruby How to identify a traditional Bourne shell? As a bonus, it is possible to write code that runs on Windows sans Cygwin. Python, Ruby and others should work just as well, too.

However, shell scripting isn't all that complicated--at least things that you should be scripting in a shell aren't all that complicated. You can do what you need to do with a fairly shallow level of knowledge. Learn how to read and set variables. How to create and call functions. How to source other files. Learn how flow control works. And most important, learn to read the shell man page. If you find yourself using shell scripting often, the pertinent info will naturally stick in your brain.

As mentioned, the GNU tools are great, and are easiest to use within the shell. It is especially nice if your data is already in a linear or tabular form of plain text.

Just as an example, the other day I was able to build a script to create an XHTML word cloud of any text file in 8 lines of Bourne Shell, which is even less powerful but more widely supported than Bash.

What I don't get is why people say bash when they mean any bourne-shell compatible shell. When writing shell scripts: always try to use constructs that also work in older bourne shell interpreters as well. It will save you lots of trouble some day. And yes, there is plenty of use for shell scripts today, as the shell always exist on all unixes, out of the box, contrary to perl, python, csh, zsh, ksh possibly?

Most of the time they only add extra convenience or different syntax for constructs like loops and tests. Some have improved redirection features. Typical pitfall: if! Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Once they are finished running the system then destroys them and there are no longer any processes representing the program cp.

When we are at the terminal we have a Bash process running in order to give us the Bash shell. If we start a script running it doesn't actually run in that process but instead starts a new process to run inside. We'll demonstrate this in the next section on variables and it's implications should become clearer. For the most part you don't need to worry too much about this phenomenon however. Running a Bash script is fairly easy.

Another term you may come across is executing the script which means the same thing. Before we can execute a script it must have the execute permission set for safety reasons this permission is generally not set by default. If you forget to grant this permission before running the script you'll just get an error message telling you as such and no harm will be done. The shorthand is often used for scripts as it allows you the owner to write or modify the script and for everyone to execute the script.

You've possibly noticed that when we run a normal command such as ls we just type its name but when running the script above I put a. We can see the current value of this variable using the command echo you'll learn more about variables in the next section. Bash only looks in those specific directories and doesn't consider sub directories or your current directory.

It will look through those directories in order and execute the first instance of the program or script that it finds. You do so by including either an absolute or relative path in front of the program or script name. You'll remember that dot. Assuming this script is in my home directory I could also have run it by using an absolute path.

This is the first line of the script above. The hash exclamation mark! Following it is the path to the interpreter or program that should be used to run or interpret the rest of the lines in the text file. For Bash scripts it will be the path to Bash, but there are many other types of scripts and they each have their own interpreter. Formatting is important here. The shebang must be on the very first line of the file line 2 won't do, even if the first line is blank.

There must also be no spaces before the or between the! Whilst you could use a relative path for the interpreter, most of the time you are going to want to use an absolute path. You will probably be running the script from a variety of locations so absolute is the safest and often shorter than a relative path too in this particular case.

It is possible to leave out the line with the shebang and still run the script but it is unwise. If you are at a terminal and running the Bash shell and you execute a script without a shebang then Bash will assume it is a Bash script. So this will only work assuming the user running the script is running it in a Bash shell and there are a variety of reasons why this may not be the case, which is dangerous. Given the observations above it is best to always include the shebang!

It is the most reliable and convenient approach. As we saw above, formatting for the shebang was important ie no spaces, must be on first line. There are many areas in Bash scripts where formatting is important. Typically it involves spaces and either the presence or absence of a space can be the difference between the command working or not.

I'll point these out as we encounter them. For example, to give read, write, and execution permissions to the owner and read permissions to the group and others would be something like this:. Now finally we have reached a mark where we can run the bash script. To run your bash script, you need to make sure that you are in the present working directory where your script resides.

Hello LinuxHint First of all, we would create a bash file in the present working directory:. Inside the file you need to write the following:. To run this file you can change its permissions to make it executable or you can write:. Echo Command When we talk about the echo command, it is simply used to print out pretty much everything that you want to print out as long as it is written inside the quotes.

Normally when you run an echo command without any flag it leaves a line then prints out the output. For example, if we have a script:. Whatever you write as a comment is nullified or ignored by the computer and has no impact at all on the written code. Comments are usually considered more of a useful way for a programmer to understand the logic of code so that when he goes back to rework on the pieces of code, those comments could remind of him the logic and reasons why he has written code in a specific way.

Comments can also be used by other programmers who might want to make changes to the code. Whenever you want to use that piece of code again, go ahead and uncomment those lines and you are good to go. There are two ways you can write comments in bash; one way is to write single line comments while the other way is used to write multi-line comments. This single line comment can be used to communicate the logic and understanding of the code to someone who has access to the code.

It would help you comment on multiple lines by just typing in 3 symbols which are handy and useful. Take a look at 30 Examples of Bash scripts on Linuxhint. Conditional Statement The conditional statement is a very useful tool in decision making.

It is widely used in programming languages. More often, we need to make decisions based on certain conditions. The conditional statement evaluates the given condition and takes the decision. In bash, we also use the conditional statement like any other programming language. The syntax of using the conditional statement in bash is a little bit different from the other programming languages. The if condition is the most commonly used conditional statement in bash and other general-purpose programming languages.

The if condition evaluates the given condition and makes the decision. The given condition is also called a test expression. There are numerous ways to use the if condition in bash. The if condition is used with else block. In case, if the given condition is true, then the statements inside the if block is executed, otherwise the else block is executed.

There are multiple ways of using the if condition statement in Bash which are the following:. The if statement The if statement only evaluates the given condition, if the given condition is true, then the statements or commands inside the if block is executed, otherwise the program is terminated. In bash, if the condition starts with the if keyword and ends with the fi keyword.

The then keyword is used to define the block of statements or commands which execute when a certain condition is true.

The -gt is used to evaluate the greater than condition whereas, the -lt is used to evaluate the less than condition.

The if else statement The if else statement is also used as a conditional statement. The statements or commands after the if condition is executed if the given condition is true. Otherwise, the else block is executed if the given condition is not true. The else block is followed by the if block and starts with the else keyword. Multiple conditions can be evaluated by using the if condition.

The nested if statement In nested if statement, we have an if statement inside an if statement. The first if statement is evaluated, if it is true then the other if statement is evaluated. The if elif statement The if elif statement is used to evaluate multiple conditions. The first condition starts with the if block and the other conditions are followed by the elif keyword.

The eq is used as an equal operator. Looping Loops are the essential and fundamental part of any programming language. Unlike, the other programming languages, the loops are also used in Bash to perform a task repeatedly until the given condition is true. The loops are iterative, they are a great tool for automation of similar types of tasks.

The for loop, while loop, and until loop is used in Bash. The while loop The while loop executes the same statements or commands repeatedly. It evaluates the condition, and run the statements or commands until the condition is true. This is the basic syntax of using a while loop in Bash. We have a variable VAR whose value is equal to zero.

In the while loop, we have put a condition, that the loop should run until the value of the VAR is less than