You will learn to:
- Create and execute simple bash scripts
- Add scripts to the
$PATH
- Bash
- Visual Studio Code
📖 We are going to be using Visual Studio Code to create and edit script files.
✏️ Install Visual Studio Code by following these instructions.
📖 Before we start, you need to create a temporary folder that will be your workspace for this workshop. Creating a folder inside your user "home" folder is the easiest way.
✏️ Open a terminal.
📖 By default, bash will set the current working directory to the value of the global enviroment variable $HOME, which will vary by OS:
- Linux:
/home/<username> - macOS and Windows (Git Bash):
/Users/<username>
✏️ To print the current working directory (which should be your home folder), use the pwd command.
✏️ Create a subfolder of your home directory called nerdschool-shellscripting by using the mkdir command.
✏️ Change the working directory to this folder using the cd command. pwd should now output <homefolder>/nerdschool-shellscripting.
✏️ To open this folder as your workspace folder inside VS Code, you can launch VS Code from the command line using the code . command.
❗ macOS-users need to follow an one-time additional VS Code setup step to add the code command to $PATH.
❗ If you receive a warning saying "Do you trust the authors of the files in this folder?", press "Yes, i trust the authors".
The result should be something like this:
📖 Notice that the left side Explorer pane of VS Code is empty, because the folder you opened is empty. To create a empty file using the command line, use the command touch <filename>.
✏️ Create a file called helloworld.sh using the touch command.
📖 In VS Code, notice that you now have a file in the Explorer pane:
📖 You can of course also create files directly inside VS Code.
✏️ Update the contents of helloworld.sh with the following using VS Code:
#!/bin/bash
MESSAGE="Hello World!"
echo "$MESSAGE"❗ Remember to save your file.
📖 The first line in the script above is something called a "shebang": #!/bin/bash. It sets the target shell to be used when executing the script. The shebang is not strictly required when creating shell scripts, but is a recommended best practice. Omitting it can some times lead to compatibility issues, as some shells have different scripting syntax than others.
📖 The last two lines in the script assigns a value to a local variable and outputs it.
📖 To execute a script, use the syntax ./<scriptname.sh>.
✏️ Try executing your helloworld.sh script this way.
📖 The command should output an error.
bash: ./helloworld.sh: Permission denied❗ If you are using Windows with barebone git bash, you shell might not honor best practice and the file may be executable from the get-go. This should not be a problem with WSL or any real Unix-like system. Try to follow along anyway, as permissions is an important aspect of working with files, that you will encounter when you are working in a non-emulated unix environment.
📖 In order for a script to be executable, you need to set the file permissons for the script file correctly.
📖 In Unix shells, scripts and programs (binaries) are both files. To be able to execute a script or a program, the correct file permissions must be set.
💡 See Addendum - File permissions learn more about file permissions.
❗ Be careful when setting file permissions, as the wrong file permissions on the wrong set of files can lead to unintended access to your system.
📖 We use the chmod command to set the permissions of files. To add the execute (x) permission to a file for the file owner, you can use the syntax chmod u+x <filename>.
✏️ Add execute permissions for everyone to the file helloworld.sh.
✏️ Check that the permissions are correct using the ls -l command. The leftmost characters on each line represents the file permission settings. The correct result should be rwxr--r--.
✏️ Try executing the script again using the ./<filename> syntax.
📖 The script should now output:
Hello World!📖 These tasks require you to create bash scripts that you can execute in your shell. Remember to set the correct file permissions on each script file you create.
✏️ Make a script that uses a for loop to print out the first few lines of each file in a directory.
✏️ Make a variable containing the path of a directory or a file that exists in your filesystem.
Make a test that checks whether the path is a directory or a regular file. Print Directory if the path is a directory, or File if the path is a regular file. Create a script that you can run to check the status of the path currently stored in your variable (e.g. ./filecheck.sh).
⭐ Bonus: Instead of storing the path of the file or folder you want to check, can you pass it inn as a parameter to the script? (E.g. ./filecheck.sh /home/myfolder).
⭐ Bonus: Are you able to use the variable containing the file or directory, printing the path of the file in the output? E.g. "/home/root/file.txt" is a file.
📖 If you create a script you want to use without executing it from the directory it is located in, you can add the script directory to the $PATH variable. Like we discussed in the previous exercise, the $PATH is set at startup and can be overridden using a .bashrc configuration file in the home directory.
✏️ Change the current directory to the home directory using cd ~. (~ is an alias of the path to the current user´s home directory)
✏️ Check to see if you have a file called .bashrc in your home directory. Create a new empty file in the home directory called .bashrc if it does not already exist.
❗ Notice that if you list the contents of the home directory the .bashrc file is hidden. This is because of the . prefix in the filename, which tells the OS to hide the file. To list hidden files using ls you can use the -a parameter.
✏️ Open the .bashrc file in VS Code using the code command and add the following:
export PATH=~/nerdschool-shellscripting:$PATHNotice that we use export to create a environment variable.
❓ Why is PATH assigned the value of $PATH?
❗ If we redefine PATH by doing export PATH=/some/dir, we loose the exiting value if we don't append it to the new value. Not retaining the predefined value of $PATH will cause the shell to not find any of the essential commands like ls and cp, which causes problems.
✏️ The .bashrc file is only read at startup, so to see if the $PATH was updated you need to start a new bash shell.
✏️ Try echoing out the value of $PATH to see if it includes the new directory we added.
✏️ Try executing some of the scripts inside the nerdschool-shellscripting directory by typing <scriptname.sh> while the current directory is any other directory.