Overview of Bash If Statement (Scripting):
If you are a coder and were asked to answer the question “Is bash if statement or scripting?” you may be trying to determine whether Bash if statement or scripting is better.
This article will help individuals with that question by looking at how they differ and relate to a programming language. While both options have unique advantages, some major pitfalls come with each. The article will explore these differences so readers can decide which option is right for them.
The first thing that needs to be explored is the differences between a bash if statement and scripting. More specifically, what is one, and what makes it different?
A Bash if statement is a unique part of the bash programming language built into its syntax. It essentially gives users the ability to make decisions within their code based on the conditions provided.
What is Bash scripting?
Scripting is a term used to describe a programming language or application that one writes. Scripting can be broken down into several types, including known script languages and unknown script languages.
While it is similar, they are still different in many ways, such as their syntax and capabilities, which explains the differences between where you place your keywords when creating scripts versus if statements within bash code.
Common special characters used in Bash if statement and in Bash scripting
“,, “”Whitespace is indicated by this symbol. Single quotes maintain literal meaning, but double quotes allow for replacements.
An expansion is denoted by the dollar sign ($). (for use with variables, command substitution, arithmetic substitution, etc.)
\
A character with the ability to flee. Used to take a special character’s “specialness” away.
# Comments. After this character, nothing is interpreted.
= Assignment
[] or [[]] Test; determines whether something is true or false.
if | command | which is equivalent of if [condition] then command else ].
* or? Globs (also known as wildcards). A single character is a wildcard.
Bash Programming Introduction
Bash is a Unix shell available on Linux and Unix-based systems through the GNU project. It was created in 1990 and has been under development by many programmers. It can be used to write scripts to automate processes that have been done manually, such as backups or file transfers. As with any programming language, there are many different ways to write code for Bash.
The syntax of the Bash if statement
There are several ways to write a bash if statement. The most common way is rather simple, as can be seen below.
if [ condition ] then commands fi
The above code provides an example of how the syntax looks when it’s not broken down. Let’s break it down step-by-step to how the code would be read in English if written out. “If the statement after in brackets is true, run all of the following commands between if and fi.”
The basic rules of bash conditions
Rules are generally attached to conditions, as seen in the above code.
All rules must be placed after the condition. Throughout this article, we’ll see that rules can also be placed before the condition if needed.
Rules are always evaluated against zero or one time. This can be seen by removing | from the condition and running it again, then splitting it, so one rule is executed at a time (only once).
Is there an else if in Bash?
No, there isn’t. Many programming languages have an else if, but Bash doesn’t. This can make statements difficult to understand for those unfamiliar with the language.
How do you write if-else in a shell script?
if [ condition ] then commands else command fi
The above code provides an example of how the syntax looks when it’s not broken down. Let’s break it down step-by-step to how the code would be read in English if written out. “If the statement after in brackets is true, then run all of the following commands between if and else; otherwise, run all of the following commands between else and fi.”
Different condition syntaxes
There are different ways to specify a condition for an if statement in bash. For example, look at the following code:
if [ x -eq 3 ] then echo “x is 3” fi
if [ x == 3 ] then echo “x is 3” fi
if [ `expr $ x = 3 ` ] then echo “x is 3” fi
if [[ $ x == 3 ]] then echo “x is 3” fi
The above code provides examples of specifying a condition in each method. Bash does allow for different conditions to be specified, but without an else if, there is no way for Bash to understand additional conditions.
Here are the three syntaxes featured by bash.
-
Single Bracket Syntax
-
Double Bracket Syntax
-
Double-parenthesis Syntax
Single bracket Syntax: It is the oldest support syntax which supports three types of conditions. File based, String Based and Number based conditions.
Double Bracket Syntax: It features Shell globbing. It is an addition to Single bracket with the asterisk (*) expanding to literally anything and few other differences like word splitting is prevented, filenames cannot be expanded, allows regex pattern. If will not allow shell globbing, if your quote the right string.
Double parenthesis Syntax: it is adopted from Korn Shell. it is another syntax for arithmetic or rather call it as number -based condition.
What is the option in if condition?
There are several different ways to specify conditions within an if statement. They are listed below with examples of each.
-a -o -z
-a Evaluates to true if the string following is not empty and the string after -a is true. The “-” at the end forces a return of 0, no matter what input is given.
The following code provides an example of how this works: if [ -z ” $ users” ] then echo “There are no users in this system. ” fi
-o Evaluates to true if the string following is not empty and the string after -o is true. The “-” at the end forces a return of 0, no matter what input is given.
The following code provides an example of how this works: if [ -z ” $ users” ] then echo “There are no users in this system. ” fi
-z Evaluates to true if the string following is empty (i.e., zero-length).
Conclusion of Bash if statement
In conclusion, the if statement works well for the bash language, but it is not without its flaws. While there is no else to be found in Bash, there are other ways to work around this issue.
The syntax of this language can be difficult to read at first. This makes it difficult for those who are just starting out as well as experienced developers trying a new language for the first time.
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