100 shell script examples

Scripts have execution rights for the user executing them. As soon as i reaches 11, the for loop will stop. http://intuitive.com/wicked/wicked-cool-shell-script-library.shtml, http://dberkholz.com/2011/04/07/bash-shell-scripting-libraries/. They are very easy to understand and utilize if you are really interested in knowing about Linux shell scripting. Conditional Statements 10. A bash script is a series of commands written in a file. If youre starting out with Bash scripting on Linux, getting a solid grasp of the basics will stand you in good stead. Keeping the system and all of its applications up to date is crucial. #!/bin/bash for ( ( i=1; i<=10; i++ )) do echo "Loop number:" $i done Following are the two main advantages of shell scripting: You can make a tax-deductible donation here. To put it simply, the bash interpreter reads the bash script and executes the commands at the same time. The parameter expansion takes the form ${VAR_NAME:S:L}. Again, the Linux date command is used for getting the necessary information, and our program does the parsing. Functions allow you to encapsulate sections of code into named routines that can be called from anywhere within your script. Its a simple program that prints the string Hello World to the standard output. This simple example demonstrates how the OR operator works in Linux shell scripts. If shell is running as root, the prompt is changed to #. You can also set certain scripts to execute on startup such as showing a particular message on launching a new session or setting certain environment variables. Line #1: The shebang ( #!/bin/bash) points toward the bash shell path. The path of the bash program can vary. You will be asked to input the filename and it will help you delete it when it exists. By submitting your email, you agree to the Terms of Use and Privacy Policy. Whats the Difference Between a DOS and DDoS Attack? . Dave McKay first used computers when punched paper tape was in vogue, and he has been programming ever since. This list of numbers starts at 3 and goes up in steps of two, then arbitrarily leaps to 44. The shell script below will show you an example of how you can count the only files you own. Users can easily add comments to their bash scripts with the # symbol. When you run a script, the current shell opens the script and determines which shell or interpreter should be used to execute that script. Any OR condition in an If statement is represented using ||. This might be up to a particular number, or it might be until the loop has worked its way through a list of items. Bash is baroque. Save my name, email, and website in this browser for the next time I comment. The versatile Bash for loop does much more than loop around a set number of times. We accomplish this by creating thousands of videos, articles, and interactive coding lessons - all freely available to the public. You can also try out using any logical conditions in an If Statement that has more than one condition. The number range is defined within curly brackets {} with two periods .. separating the numbers that start and end the range. The following examples show this in action. In a similar way to using the number range, we can use a file pattern in the loop header to specify the files we want to process. However, our editors have also tried to outline some shell script examples that deal with shells other than bash. This is infinite.sh.. It instructs the operating system to use a bash interpreter as a command interpreter. It adds an additional line to the earlier editors.txt file. His writing has been published by howtogeek.com, cloudsavvyit.com, itenterpriser.com, and opensource.com. The for loop is another widely used bash shell construct that allows users to iterate over codes efficiently. To get the value of the variable, add $ before the variable. $cat > geekfile.txt Rather than type the same set of instructions into your script, again and again, a loop will repeat one section of code over and over for you. $ bash hello.sh. This script is associative.sh. It defines an associative array with four entries in it, one for each of dog, cat, robin , and human. These are the keys. Run the script to see what it does. You need to run this script using sudo else it will not work properly. During his career, he has worked as a freelance programmer, manager of an international software development team, an IT services project manager, and, most recently, as a Data Protection Officer. How to automate scripts by scheduling via cron jobs. How to Process a File Line by Line in a Linux Bash Script, How to Deal With Spaces in Filenames on Linux, Intel CPUs Might Give up the i After 14 Years, Windows 11 Has More Widgets Improvements on the Way, 10 Inexpensive Ways to Breathe New Life Into an Old PC. The script is a series of commands that will be run together. There are some instances you will need to check for the last updated file. You can simply use this particular script to delete every log file present in your var/log directory. If the log file is connected to a server process, you might need to stop the process before the rotation and start it again after the log rotation is complete - this is not the case with rotate.sh. Modify the file permissions and allow execution of the script by using the command below: chmod modifies the existing rights of a file for a particular user. Just as we have said for adding values together above, multiplying numbers in Linux shell script doesnt appear difficult. The OR operator is another crucial construct that allows us to implement complex, robust programming logic in our scripts. Bash supports the classic three-term for loop, such as those found in the C programming language. After over 30 years in the IT industry, he is now a full-time technology journalist. Variable names (which are actually pointers), if passed as parameters to functions, will be treated as string literals. Replace script1.sh with the name of your script. The wait command is used with a particular process id or job id. Shebang is a combination of bash # and bang ! The program executes line by line. Most of these examples are for sh . This script prints the same number using three different numerical bases. The first bash if example provided in this tutorial ( test_script.sh) works equally well with the alternative syntax: echo -n "Please enter a whole number: " read VAR echo Your number is $VAR if [ $VAR -gt 100 ] then echo "It's greater than 100" fi echo Bye! The output was then printed via the echo command. This saves you time because you don't have to write certain commands again and again. We can combine the prompts into the read commands using the -p (prompt) option. Let's have a look at the 35 Bash script examples: 1. The last loop works through the list of words in a string variable. The examples to be implemented in PowerShell Scripts are explained below: Example #1: Adding Users to AD The following script will add each user present in a CSV to the AD. The image below explains how it can be done. A shell script is a set of instructions / commands (program) designed to be run by the Unix/Linux shell. For finding the number of files or folders present within a directory, try out the following script below. The body of the loop performs a string comparison test. Work vector created by macrovector - www.freepik.com. Since we launched in 2006, our articles have been read billions of times. For this reason, bash scripting is the go-to choice for increasing productivity, setting up automation, and eliminating repetitive tasks. The iterator is called legs . A shell script example for receiving user input within a shell program You can easily use the $ sign to have access to the input stored 8. This program will simply delete all log files present inside your /var/log directory. All parts separated by an AND operator must be true. For instance, if we run "Hello World" in our terminal, the output we get will be "Hello World." First Bash Program The Notes, examresults, and portfolio subdirectories are also created inside each. If the answer is 0, the number is even. As most of the scripts end with .sh, we can use the find script like this: If you are interested to read about the find command in detail, check my other post. For example, check the below bash script example. Tests 8. The fi keyword is used for marking the end of the if statement. All Rights Reserved. And without the executable permission being set on the script, the ls command wont identify it as an executable file, nor will it use color to distinguish the script from plain text files. A quick example is shown below. The switch command is a strong Linux bash script feature. His current goal is to write easy-to-follow articles so that these issues will not happen at all. Getting user input is crucial to implement user interaction in your scripts. The body of the loop is going to print that value to the terminal window. The above program will only show the output if the number provided via input is greater than ten. The Linux cut command can be used inside your scripts to cut a portion of a string, aka the substring. It will list either the last updated or created file in your current working directory. Instead, you can simply copy this code to get the task done. To save time and energy, try out the following program below. What do we understand by shell scripting? Well ask for filenames that begin with n and have an SH extension. Create a file named evenoddnumbers.sh: The script uses the read command to read user input and divides it by 2. The break command breaks out of the loop and prevents any more processing. For example, you can navigate to a certain path, create a folder and spawn a process inside it using the command line. This tutorial is written to help people understand some of the basics of shell script programming (aka shell scripting), and hopefully to introduce some of the possibilities of simple but powerful programming available under the Bourne shell.As such, it has been written as a basis for one-on-one . It is possible to use Linux Cut Command inside a script to cut some parts of the string. Do so with the following command: Running the script results in this output: Well print a file with its line count. Functions interpret their arguments literally. As a result, youll find a substantial amount of familiarity between different shell scripts. Writing text to the terminal is a common requirement. The next shell script example shows how to check the existence of a file from bash programs. Bash scripts can be used to tell if a user is root or not. When we run it we get the statistics for each file, with the files listed in alphabetical order. It's not fair to say that bash has evolved either: it retains and utilizes all of its vestigial appendages. Version 1: Explicit For loop We use a for-loop to iterate over all files provided as arguments to the script. What do you understand by the term bash? String processing is of extreme importance to a wide range of modern bash scripts. The best way to learn something is by doing it. wait is a built-in Linux command that waits for completion of running process. 100-shell-script-examples has a low active ecosystem. So, $1 is used for accessing the first argument, $2 for the second, and so on. Writing good scripts means using the most suitable tool for the task at hand. Below are some examples of scheduling cron jobs. The below simple shell script will show you how to do this. It is useful in a wide variety of scenarios. Line #5: The read command reads the input and stores it in the variable the_path. Plus, you need to provide the directory name of your files as a command-line argument. Make sure you dont include any whitespace in the range definition. Here weve added two numbers just like before. The following simple example will show you how to create a directory from within a shell script. These are read and executed by the bash program. Finally, it prints the string contained in the millennium_text variable and the numerical value stored in the years_since_Y2K. It is extra useful if users need to store and retrieve thousands of pieces of data fast. The loop body accesses the value in the word variable and so each word in the list gets processed. The first line must start with a shebang, #!, also known as a hashbang. Thank you! The only line in the script writes the value held in the $SHELL environmental variable to the terminal screen. echo Logs cleaned up. These shells include Bash, Zsh, Tcsh, and Ksh, etc. It holds what you want the loop todo. If you have a command or sequence of commands that produce a list of something, such as filenames, you can iterate through them with a for loop. A for loop lets yourun a loop a number of times. The iterator steps through the number range in jumps of four. The third loop works through a list of words. Its pretty dope! Are you sure you want to create this branch? It will be approved within the next 24 hours. Line #2: The echo command is displaying the current date and time on the terminal. We need to provide a counter statement that increments the counter to control loop execution. Find out how elif works by assessing the following example. As a bit of a parlor trick, we can demonstrate that the script is passed to any interpreter we select. Join 425,000 subscribers and get a daily digest of news, geek trivia, and our feature articles. The below Linux bash script finds the number of files or folders present inside a given directory. It is required to search through the array. First, create the bash script file: Make sure to preface the script with the sudo command when you run it: Important!Apt package manager is used on Debian based distributions only. When the iterator contains Arch the for loop abandons any more processing. In contrast to certain other programming languages, shell scripts normally pass only value parameters to functions. Indirect variable references (see Example 34-2) provide a . The AND operator allows our program to check if multiple conditions are satisfied at once or not. By adding a case for each selection, the script can execute separate tasks based on what the user selects. The most simple example would be the following: The above script will connect the values of firststring and secondstring variables creating a whole new thirdstring. Otherwise, if the single quotation marks are used, it will print out only the name of a variable. File processing takes considerable time and hampers the productivity of admins in many ways. This article will contain a higher percentage of bash compared to other varieties of shell scripting. This script, number-range2.sh will use a range of 0 to 32, and a step size of 4. The execute permission can be set with the +x flag. Suppose we have a file sample_file.txt as shown below: We can read the file line by line and print the output on the screen. Next, you need to make this file executable using the below command. This script is "c-like.sh." The iterator I is set to 1 at the start of the loop, and the loop will run for as long as the statement " i<=10 " is true. When we run it, the script prints the two-legged creatures. How to create your first bash script and execute it. Try it out now! Lots of advanced bash scripts take full advantage of string processing. The following simple example will demonstrate one way of doing this from bash applications. So, to run a script without a shebang, without the executable file permission, and without launching another shell, you can use either of these commands: Although this is possible, it isnt recommended as a general solution. It is used in places that there is a need for nested conditions. The continue command abandons thecurrentspin of the loop. Since [ is a command (you could also use 'test'), it requires a space before writing the condition to test. This is called the shell prompt. Start by creating a .sh file executable: The following script will ask the user to enter a number they want to get the factorial of and use a for loop to calculate it. Executable scripts appear in a different colour from rest of the files and folders. This script is command.sh. it uses ls and wc to provide a sorted list of script file names, together with their line, word, and byte counts. Special Characters 4. How-To Geek is where you turn when you want experts to explain technology. Its called the shebang and lets the system know which interpreter to use when running this script. It uses $2 to show how to access a single, particular parameter value. It also has numerical tests for equals -qe, greater than -gt, less than or equal -le, and so on, although you can also use the familiar == , >= , <= notation. The following script will list a few important server metrics: systems date, uptime as well as memory, and network usage statistics. Take Screenshot by Tapping Back of iPhone, Pair Two Sets of AirPods With the Same iPhone, Download Files Using Safari on Your iPhone, Turn Your Computer Into a DLNA Media Server, Add a Website to Your Phone's Home Screen, Control All Your Smart Home Devices in One App. The script behaves slightly differently now. Performing arithmetic operations in Linux shell script can be very easy as you can ever think of. Sometimes you'll need to gather user input and perform relevant operations. First, check how comments are used using # before some lines. What is SSH Agent Forwarding and How Do You Use It? However, power users who have specified choices often use other shells such as Zsh and Ksh. We can add some more flexibility by passing in the filename pattern on the command line. Scripts that are easy to read are also easier to debug. Create a new file: Then, paste in the following code it creates a simple Hello World function. Nothing in the function is run until the function is called. Filename patterns are expanded, and all of the filenames are processed in the loop body. If you use the source command, which can be abbreviated to a single period ., your script is executed by your current shell. 2. This confirms that Bash was used to execute the script. You can achieve this using the find command, The result of this program depends heavily on whoever is running it, The shell script will carefully scan through every line in your files to search and find out duplicated lines, You need to use Sudo to make the program run better and more efficiently. All the code is open source, and you can copy and paste the examples to learn. It has proven to be one of Unix's major features throughout the years and grew into a whole new topic itself. The script prompts for two numbers. Docker Cheat Sheet: All the Most Essential Commands in One Place + Downloadable PDF, What Is PHP.ini File, and Where Its Located? Create a invoke.go file with the following contents: A function is very important in Linux shell scripting just the way it is with every other programming languages. You are going to be shown how to get command line arguments with their names here. The best way to learn is by practicing. The output should be in the format of Day, Date, year time. Create a file named ide.txt with the contents given below, This script will give out the above 3 lines as an output. A loop is an essential tool in various programming languages. A shell script is a computer program designed to be run by the Unix/Linux shell which could be one of the following: The Bourne Shell; The C Shell; The Korn Shell; The GNU Bourne-Again Shell; A shell is a command-line interpreter and typical operations performed by shell scripts include file manipulation, program execution, and printing text. Hello World is the most simple bash script to start with. Knowing how to read data from a file is a great skill to have. By submitting your email, you agree to the Terms of Use and Privacy Policy. To check conditions, we can use if, if-else, if-elif-else and nested conditionals. Line #4: We want the user to enter a valid path. I'm not the author. We will name it 'list.sh' and to run it in the terminal we will use the below command: $ bash list.sh. If the value of the array member is Two-legged, it prints the key value to the terminal window. The space surrounding the square brackets is mandatory. I highly encourage you to follow along using Replit. Below is an example of the shebang statement. The superuser shell prompt looks like this: Bash is very powerful as it can simplify certain operations that are hard to accomplish efficiently with a GUI. SED is a powerful text stream editor. 100 interesting shell scripting problems Hi all, I'm just learning to write shell scripts (new to the whole UNIX thing) and I'm wondering if anyone would like to help me create a resource to help me, and others like me, learn scripting. We have already covered Vim and awk is in the pipeline. Even though the if statement is easy to write and understand, it can be used in advanced shell scripts as well. It then creates three numerical variables. 1. You can run the script any number of times. The following simple program shows us how to do this in bash using the awk command. The next example shows the sleep command in action from within a shell script. You can include another number that defines the step size the iterator should use to walk through the numbers in the range. We can also pass in more than one pattern at a time. Instead, change portions of the script like variable names and values to check how they function together. These examples elaborate specific shell features. Ive programmed this script to add (.UP) at the end of the files. Because of the two-way relationship between the key and the value, theyre also called data dictionaries. For example, to run a nonexecutable file named script1 under the control of the Korn shell, type the following: ksh script1. Well check how many inodes there are in a directory, as too many can cause the system to slow down significantly. They are read from the keyboard and stored in two variables, user_number1 and user_number2 . Create an Array 9. This script will output the number 60. The statements are only executed given the CONDITION is true. For example, you can use a bash array to store both strings and numbers. These two parameters are passed into the function just like parameters are passed into a script. Below are the operators supported by bash for mathematical calculations: Numerical expressions can also be calculated and stored in a variable using the syntax below: Fractions are not correctly calculated using the above methods and truncated. Example: You can easily use the bash scripts to append data to any file on your filesystem. [SCRIPT] [INPUTFILE.] The script will get the directory name from the user and will check if it already exists or . The output of this script depends on the user running it. We describe its many variants so you can use them successfully in your own Linux scripts. They are relatively not difficult. It utilizes the Linux find command to do this. The below example demonstrates how to do this in bash. Loops and Branches 12. This loop starts at 15, and counts backward in steps of 3. The for loop is a great tool to have in your toolbox of tricks. Create a bash file for it: The script prints out numbers from 2 to 10 while adding the seconds keyword to it. Save and quit the file. There are 30 watchers for this library. As you can see, adding numbers in bash is reasonably straightforward. The above program is self-explanatory, so we wont dissect it line by line. In this section, we will study the syntax of bash scripting. Dont be dazzled into thinking the for loop is all youll ever need. Bash is a command-line interface interpreter that runs in a text window where users can manage and execute shell commands. What you do with it after that is up to you. The test for whether the loop continues or ends. The cat command runs the script. We create the AWK scripts by using #!, followed by the absolute path of the AWK interpreter and the -f optional argument. What makes bash arrays special is that unlike any other programming language, they can store different types of elements. Script #1: Hello World Hello World programs are the most basic programs that help programmers learn a new language. It would be pretty pointless to have a script that only does what ls can do, but it does demonstrate how to access filenames inside the loop body. There was a problem preparing your codespace, please try again. There are likely to be incompatibilities. The structure of conditional statements is as follows: To create meaningful comparisons, we can use AND -a and OR -o as well. It is never easy to search and find duplicated lines in a file. It has proven to be one of Unixs major features throughout the years and grew into a whole new topic itself. Ive named it test.sh and the calling procedure is outlined below. File: rotate.sh. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Please fill the required fields and accept the privacy checkbox. The following example will backup each file or directory that have been modified within the last 24 hour. Bash or shell scripting on the other hand is the process of writing a set of commands to be executed on a Linux system. In order to check if a given file exists, users can perform conditional tests. The arguments here are stored inside [emailprotected] and the script fetches them using the Linux cut command. The script prints the time and date, then calculates how many years have passed since the millennium, and stores this in the years_since_Y2K variable. Even if it doesnt, that last line will be handled correctly and treated as a regular POSIX-compliant line. In this tutorial, weve covered the basics of bash scripting and how can it be used to automate tasks and increase productivity. Suppose we wanted our script that reads lines from a file to do some sort of processing on each line. The article we will be looking at here will definitely make familiar and a great user of Linux. This script is launched by the current shell and passed to the cat command. Theyre the foundation of deeper knowledge and higher scripting skills. With it, it's still a text file, but the shell knows it contains instructions and will try to execute them when the script is launched. The below example demonstrates how to receive two numbers as input from the user and add them. Work fast with our official CLI. The examples that will be given here will definitely help you understand shell scripting better. Shebang is simply an absolute path to the bash interpreter. A shell script is a command-containing text-file that contains commands in order of their execution. The If Statement is one of the most popular conditional constructs found in Unix shell scripting. Youll need to do this to each of your scripts. It returns false only when each operand separated by the OR is false. So, try these simple examples yourself to gain the first-hand experience. It can work with numbers, words, arrays, command line variables, or the output of other commands. The ability to run system commands using shell scripts allows developers to be much more productive. A file that includes such instructions is called a bash script. The below shell script example will show you how to append data to a file on your filesystem using bash scripts. Functions 11. Get User Input 7. When you purchase through our links we may earn a commission. The function definition doesnt cause any code to be executed. Dave is a Linux evangelist and open source advocate. The Linux command line is provided by a program called the shell. This can be done via the cut command. This program should create a directory in your filesystem. This program should print out the numbers 1 to 10. This is followed by a unique name for our function followed by parentheses (). The body of the function is contained within curly brackets {}.. for the current working directory. 40 Simple Linux Shell Script Examples Shell_script.png. Run this program yourself to check out how it works. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Weve modified our file reading program by adding a function called count_words. Sometimes it is more convenient to accept user input as command line parameters than to have a script sit waiting for input. The example in the picture above shows how to use shell script to back up a directory in Linux, You can use eval to increase your bash shell scripting while writing this program, One of the very possible ways of doing this is shown in the commands above, You can easily try it out by following the instructions above, Try out the above program out now to see it executes.

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