100 shell script examples 100 shell script examples

Creating simple yet effective Linux shell scripts for tackling day-to-day jobs is quite easy. Run this program yourself to check out how it works. The following example will show you how to create a directory from within a shell script. And 99% of the time, thats fine. It would be convenient to have that code contained within a function. #!/bin/bash for ( ( i=1; i<=10; i++ )) do echo "Loop number:" $i done The slicing of a string in bash is done without the provision of an in-built function. However, the examples shown should also work for bash and other shells in most cases (if not, equivalent syntax can be determined). Are you going to remember in a years time? It is used in places that there is a need for nested conditions. As a reader of this book, you are the most important critic and commentator. Then, finally, the $# is used for getting the total number of arguments. What is SSH Agent Forwarding and How Do You Use It? They can be referenced inside the script as if they were any other variable. Getting user input is crucial to implement user interaction in your scripts. crontab -l lists the already scheduled scripts for a particular user. The AND Operator does the work of checking if multiple conditions are met at a time or not. 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. You can create a bash script to do it. Check user running script Command to do nothing Let's create our first shell script. For this reason, bash scripting is the go-to choice for increasing productivity, setting up automation, and eliminating repetitive tasks. The wait command is used for pausing system processes from Linux bash scripts. 4. Passing values to a script is easy. This allows the loop to work with the values of each of the data items in turn, or even in some cases to manipulate the data items themselves. Many people use multi-line comments for documenting their shell scripts. As a bit of a parlor trick, we can demonstrate that the script is passed to any interpreter we select. Below are some examples of scheduling cron jobs. It will send an email to the recipient containing the given subject and message. Run the script to confirm the output is equivalent. Create a new directory and put some files in there for demonstration purposes. It features over twenty useful bash script examples to start your bash scripting journey. When you purchase through our links we may earn a commission. The below demonstration will outline how functions work in Linux bash scripts. Bash supports the classic three-term for loop, such as those found in the C programming language. Automation in Linux heavily relies on cron jobs. Since [ is a command (you could also use 'test'), it requires a space before writing the condition to test. Functions 11. Shell Scripting Tutorial You can easily use the bash command to print out the information you want in bash. The above program will only show the output if the number provided via input is greater than ten. All the code is open source, and you can copy and paste the examples to learn. Make sure you dont include any whitespace in the range definition. Variables allow you to store values inside your program and to manipulate and use them. The below example demonstrates how to receive two numbers as input from the user and add them. Heres a simple example. Firstly, do not try this script from any regular directory; instead, run this from a test directory. With this method, you can concatenate strings with only one variable. 1. First, create a file called editors.txt with the following contents. 40 Simple Linux Shell Script Examples Shell_script.png. Advanced Bash Shell Scripting Guide - Complex Functions - Linuxtopia The echo bash command can be used to print out text as well as values of variables. We can craft a statement like this: df -h | grep tmpfs. One good thing about these subsets of shell scripting is that they are all relatively easy to program. It is similar to the C function printf and provides many common options, including escape sequences and re-direction. 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. 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. It adds an additional line to the earlier editors.txt file. The fi keyword is used for marking the end of the if statement. Odd and even numbers can be easily divided using the if statement and some simple math. This is important because if youve written a script to run in Bash, you dont want it to be interpreted by a different shell. It then places the new content into a new file and keeps the original file intact. Highlight a Row Using Conditional Formatting, Hide or Password Protect a Folder in Windows, Access Your Router If You Forget the Password, Access Your Linux Partitions From Windows, How to Connect to Localhost Within a Docker Container, How to Run Your Own DNS Server on Your Local Network. We can do this in Bashwith a while loop. The while loop sets the internal field separator to an empty string, using the IFS='' assignment. The script below will serve as a guide in showing you how to apply the custom extension to every file in a directory. 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. The above program will not work if your current working directory already contains a folder with the same name. It is extra useful if users need to store and retrieve thousands of pieces of data fast. The echo command is used for printing out information in bash. So, $1 is used for accessing the first argument, $2 for the second, and so on. Let's create a simple script in bash that outputs Hello World. By submitting your email, you agree to the Terms of Use and Privacy Policy. Useful Script Examples - Learn / Linux Shell - Open Water Foundation By adding a case for each selection, the script can execute separate tasks based on what the user selects. It holds a line of text. While the value of i is less than or equal to the value held in $1, the loop will continue to run. This saves you time because you don't have to write certain commands again and again. All scripting and programming languages have some way of handling loops. In Bash 4 and higher, associative arrays allow you to create lists of key-value pairs that can be searched by the key or by the value. All parts separated by an AND operator must be true. Each text file, video, folder, HTML file, or script is 1 inode. Create an Array 9. Operations and Related Topics Part 3. Number ranges let you specify the first and last number only. If the value of the array member is Two-legged, it prints the key value to the terminal window. See the below example for a glance into bash string concatenation. What Are Bash Dictionaries on Linux, and How Do You Use Them? If youre looking to write your first for loop, these simple examples will get you started. The examples that will be given here will definitely help you understand shell scripting better. 30+ awk examples for beginners / awk command tutorial in Linux/Unix Write this program using eval to increase your bash scripting skills. How to if/else statement in shell script - Stack Overflow And the reason for this is because bash is more popular and it is more used compared to others. What Is Bash Scripting Used For 25 Bash Scripts Examples 1. In order to check if a given file exists, users can perform conditional tests. Hello World 2. On Ubuntu 20.04, the installation command will look like this: Once youve taken care of the mail transport agent installation, create a new bash script: Important! Shell scripts provide an easy way to carry out tedious commands, large or complicated sequences of commands, and routine tasks. Executable scripts appear in a different colour from rest of the files and folders. 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. How-To Geek is where you turn when you want experts to explain technology. This script is called filenames.sh.. The below example will showcase how to read a file using shell scripts. Scripts that are easy to read are also easier to debug. Suppose we wanted our script that reads lines from a file to do some sort of processing on each line. Bash or Bourne-again shell is one of the most popular shells and command languages for Linux VPS enthusiasts. The AND operator allows our program to check if multiple conditions are satisfied at once or not. By submitting your email, you agree to the Terms of Use and Privacy Policy. The values are the (default) number of legs they each have. Bash simply means Bourne Again SHell. Start by creating the bash script: Paste in the following code it will check inodes in descending order as well as show disk usage in a given directory: It will look something like this on the command line: The given directory has 15 inodes and all files take up 20KB. When you run a script, the current shell opens the script and determines which shell or interpreter should be used to execute that script. This script, number-range2.sh will use a range of 0 to 32, and a step size of 4. Because you choose the shell on the command line, theres no need for a shebang. Comparison is used to check if statements evaluate to true or false. You can easily use the Sleep command to make a break between instructions. A shell script is a set of instructions / commands (program) designed to be run by the Unix/Linux shell. To be completely factual, there is a way to run scripts without a shebang, and without making them executable. As with any programming dialect, functions play an essential role in Linux shell scripts. The next shell script example shows how to check the existence of a file from bash programs. We will create a new variable called learningbash and print out the words Hello World. Part II contains 100 programs (including shell script and programs in C). Or $ chmod a+x hello.sh $ ./hello.sh. The 40 Simple Yet Effective Linux Shell Script Examples - UbuntuPIT In the PowerShell example, we will discuss how will Get-Date and Set-Date using PowerShell. This script prints the same number using three different numerical bases. 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. 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. You can use loops to get multiple user input and add them to your script. 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. Run this program to see how it works. When you purchase through our links we may earn a commission. The arguments here are stored inside [emailprotected] and the script fetches them using the Linux cut command. We select and review products independently. Here, S denotes starting position, and L indicates the length. How to Create Your First Bash Script The below example will apply a custom extension to all of the files inside a directory. Hello World is the most simple bash script to start with. To put it simply, a bash loop is a set of instructions that are repeated until a user-specified condition is reached. The next bash script example will show you how to handle dates and times using scripts. It will print out the string passed to echo inside the script. Luckily, you can do this with a short shell script. In this tutorial we learned the basics of shell scripting. Cron is a job scheduling utility present in Unix like systems. For finding the number of files or folders present within a directory, try out the following script below. I'm not the author. This simple example demonstrates how the OR operator works in Linux shell scripts. 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. During his free time, Ignas likes to play video games and fix up things around his house. It has 458 star (s) with 509 fork (s). To save time and energy, try out the following program below. As a result, youll find a substantial amount of familiarity between different shell scripts. In the below PowerShell script example, you'll see a great example of performing some comparison logic followed by an action. We can also pass in more than one pattern at a time. You need to watch out for unexpected filename expansions, but in simple cases it is fine. So, the reading construct, followed by a variable name, is used for getting user input. 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! 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. Check how this is done in the next script called comment.sh. The first parameter becomes function variable $1, and the second parameter becomes function variable $2, and so on. The #! tells the shell that this line contains the path and name of the interpreter that the script was written for. It should delete the file. When the iterator contains Arch the for loop abandons any more processing. 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. Even if you are a casual user, you can make your life easier by automating simple tasks like updating packages or putting your system to sleep. Bash Scripting Tutorial - Linux Tutorials - Learn Linux Configuration It is required to search through the array. 35 Bash Script Examples | FOSS Linux Dont forget to make it executable. The above code will only run if you insert the code below. 9 Examples of for Loops in Linux Bash Scripts - How-To Geek It has proven to be one of Unixs major features throughout the years and grew into a whole new topic itself. You are very likely to become more productive when you use shell scripts to execute system commands. I am a DevOps Consultant and writer at FreeCodeCamp. freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. In bash, we can take user input using the read command. The condition that ends this loop is when i has iterated across the entire list of numbers. Its quite easy to perform arithmetic operations inside Linux shell scripts. Our mission: to help people learn to code for free. Do so with the following command: Running the script results in this output: Well print a file with its line count. If the shell happens to be in a non-standard location, this type of approach can avoid bad interpreter errors. You will be asked to input the filename and it will help you delete it when it exists. The first line is an exception, though. For counting the number of lines in one file we use wc -l . The Shell Scripting Tutorial For decimal calculations, we can use bc command to get the output to a particular number of decimal places. The Linux cut command can be used inside your scripts to cut a portion of a string, aka the substring. cat /dev/null > wtmp Simple Linux Shell Script Examples While there are more words to process, the loop keeps repeating. 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. This is the first line of the script. A bash array is a data structure designed to store information in an indexed way. 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Here, * represents minute(s) hour(s) day(s) month(s) weekday(s), respectively. Weve also listed 25 of the most common simple bash scripts that you can try out. cd $LOG_DIR. All Rights Reserved. The following example will backup each file or directory that have been modified within the last 24 hour. What do you understand by the term bash? For example, searching for duplicates in your files can become a daunting task. Quickstart: Deploy a shell service to Cloud Run | Cloud Run Line #4: We want the user to enter a valid path. This term simply means scripting in any sort of shell. The -e option is used for telling echo that the string passed to it contains special characters and requires extended functionality. Work fast with our official CLI. The count_words function prints the number of words in a line of text, and the line number. Variable $@ is a string that contains all of the command line parameters. Sleep Command 4. 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. This script simply calls your standard shell command mkdir and passes it the directory name if you look closely. Once you get some re-usable techniques under your belt youll be able to write worthwhile scripts relatively easily. It is possible to give arguments to the script on execution. Conditional Statements 10. The loop body accesses the value in the word variable and so each word in the list gets processed. My folder has a total of five files, each named test followed by (0-4). You can simply use this particular script to delete every log file present in your var/log directory. Bash or shell scripting on the other hand is the process of writing a set of commands to be executed on a Linux system. There are 30 watchers for this library. The first line of a script tells the shell which interpreter should be called to run that script. The loop body can contain any valid script command. 100 interesting shell scripting problems - UNIX The while loop reads each line from the file and passes it to the count_words function, together with the line number. However, omitting the (( )) will result in string concatenation rather than addition. Were passing the name of the file we want the script to process as a command line parameter. To include it in the bash script, we can enclose it in back ticks. Itll be the only parameter, so inside the script $1 will hold the filename. The best way to learn something is by doing it. We can iterate through an associative array using a for loop. When a shell is used interactively, it displays a $ when it is waiting for a command from the user. We'll mostly stick with Linux bash scripts in our examples due to their widespread popularity and immense usability. All of these loops are for loops, but theyre working with different types of loop statements and data. Take a look at the next example. Create a file named evenoddnumbers.sh: The script uses the read command to read user input and divides it by 2. Work vector created by macrovector - www.freepik.com. The input is stored inside this variable and can be accessed using the $ sign. His articles are carefully crafted with this goal in mind - making complex topics more accessible. Plus, you need to provide the directory name of your files as a command-line argument. Try it out now! If shell is running as root, the prompt is changed to #. We hope this article has helped you understand bash scripting better. The function definition starts with the word function.