#Unix shell scripting basics how to
#Unix shell scripting basics code

#Unix shell scripting basics code

If the exit code is not zero, the script informs the user that Apache isnвЂ™t running. We then check to see if the exit code isnвЂ™t equal to zero as this would indicate that the ps command did not get a response. In this script, we look to see if Apache is running, but send the output from the check to /dev/null. If an exit code has a value other than zero, an error occurred. The trick is to check the exit codes after commands are run. You can detect and react to errors within scripts and, in doing so, avoid other errors. Only after that does it bother with the extraction. Note that this script also prompts for a file name if none was provided and then checks to make sure that the file specified actually exists. *) echo вЂњNo extract option for $filenameвЂќ In the script below, we use different commands to extract the contents of the file provided as an argument by identifying the file type. #!/bin/bashД¬ase statements allow your scripts to react differently depending on what values are being examined. Use while when you want to loop as long as some condition exists or doesnвЂ™t exist. Use for when you want to loop a preset number of times. There are a number of ways to loop within a script. To check that the number of arguments provided is correct, you could use syntax like the following that checks to be sure at least two arguments have been provided and, otherwise, reminds the user that both a number of lines and file name are required: #!/bin/bash Otherwise syntax like what is shown above would fail because the shell would see вЂњif * ]] вЂќ which would generate a syntactical error. If the response is numeric, we then assign it to the variable $loops to use later in the script.ДЄnother useful thing to do in a script is to first verify that there are arguments. In this case, weвЂ™re checking to be sure that the first argument provided is numeric and exiting the script if it is not. For any argument that youвЂ™re going to use repeatedly, you might consider assigning those values to more meaningful variable names. Script arguments will be assigned the names $1, $2 and so on.

#Unix shell scripting basics how to

To make use of arguments that a user enters along with the script name, you need to know how to identify them. The person running the script will see the prompt and provide their response: How many loops?> 11 You can also determine your primary shell by checking the /etc/passwd file: $ grep $USER /etc/passwd To determine which shell you are using, use this command: $ echo $SHELL ThereвЂ™s even one called fish that can be especially nice for Linux beginners because of its helpful command auto-completion options. Д«ash is one of the most popular, but thereвЂ™s also zsh, csh, tcsh and korn. It reads commands and sends them to the kernel for processing. Unix and Linux systems today have a number of shells that you can use. In this post, we look at scripting basics-at how to get started if you have never built a script before. Creating a script on a Unix or Linux system can be dead easy or surprisingly complex it all depends on how much youвЂ™re trying to get the script to do.