The purpose of saving such commands as scripts is to save time: if you are planning. This encourages 'bad behavior', like initializing aliases in your profile script when they should live in your rc script as that runs on non-login shells.USING SHELL SCRIPTS Shell scripts can be as brief as one-line commands. Unfortunately, unlike in Linux, standalone macOS terminals all run as login shells by default, since macOS does not run a login shell when the user logs into the system.Environment variable syntax and best practices In addition to the basics of command line use and shell scripting. How to change and set environment variablesFor this tutorial, I have downloaded STS 3.8.3 for Mac (based on Eclipse 4.6.2). Zsh offers some unique features like file globbing, loadable modules, path expansion, startup/shutdown scripts, and more.
How to set an environment variable to be read-onlyThe values of environment variables can control the behavior of an operating system, individual utilities such as Git, shell scripts, user applications such as the Google Chrome browser, or deployed applications such as a Python web app.Let's look at the basics for setting and accessing environment variables using the following commands: # Setting an environment variable # The `export` keywords essentially means "make this globally accessible" # No spaces on either side of the equals sign. How to execute a command or script in a "clean" environment How to pass through environment variables when using sudo How to execute a script in the context of the current shell Using environment variables for application secrets and credentials What option to use when formatting a disk to be used for both mac and windowsWOOKIE= "Chewbacca"We can also verify this behavior this using a non-shell language such as Python: WOOKIE= "Chewbacca"Python -c "import os print(os.environ.get('WOOKIE'))" # > NoneEnvironment variables, on the other hand, are designed to be accessible to scripts or child processes and differ from shell variables by use of the export command. # In a new shell echo "The Wookie's name is $WOOKIE" # > The Wookie's name isThe same rules apply to scripts, for example, if a file shell-var-test.sh contained the following: # shell-var-test.sh echo "The Wookie's name is $WOOKIE"And shell-var-test.sh was run even after NAME was defined, it's not accessible to the script. # Shell variable as it does not use the `export` commandWOOKIE= "Chewbacca" echo "The Wookie's name is $WOOKIE" # > The Wookie's name is ChewbaccaIf you opened a new shell and ran the echo command, the NAME variable does not exist as it was scoped to the previous shell only. Difference between shell and environment variablesSimplistically, shell variables are local in scope whereas environment variables are global, but let's explore this further with examples.Shell variables should be used when they are only needed in the current shell or script in which they were defined. How to delete an environment variableThe unset command is used to remove a variable: export FAV_DROID= "R2-D2" echo "My favorite droid is $FAV_DROID" # > My favorite droid is R2-D2 unset FAV_DROIDEcho "My favorite droid is $FAV_DROID" # > My favorite droid isThe deletion of an environment variable only affects the current shell. You've most likely seen this used before in a ~/.bash_profile or ~/.bashrc file when appending a directory to the $PATH variable: # Add the `~/bin` directory to $PATH for user scripts and self-compiled binariesNote that we did not put export before PATH in this example, and that's because PATH was already exported, so putting export again does nothing. How to change and set environment variablesChanging an environment variable is no different from changing a shell variable: export FAV_JEDI= "Obi-Wan Kenobi" echo "My favorite Jedi is $FAV_JEDI" # > My fav jedi is Obi-Wan KenobiFAV_JEDI= "Rey Skywalker" echo "My favorite Jedi is now $FAV_JEDI" # > My favorite Jedi is now Rey SkywalkerYou can also modify a variable using its original value to create a new value. Pokemon ruby mac emulatorAlways surround variables usage with quotes, e.g. Always surround values with quotes, e.g. The naming convention is CAPITALIZED_SNAKE_CASE No spaces on either side of the equals sign Variable names may only contain characters (a-z,A-Z), numbers, and underscores Shell Program How To Do ThisLet's try running our script twice using & syntax: BABY_YODA= "Grogu" bash baby-yoda.sh & bash baby-yoda. Setting environment variables for a single commandSometimes, you'll want to expose or change environment variables only for the life of a single command, script, or child process.To demonstrate, we'll use the following script baby-yoda.sh: # baby-yoda.sh echo "Baby Yoda is named $BABY_YODA"First, let's look at how to do this the long and inefficient way: export BABY_YODA= "Grogu"# > Baby Yoda is named Grogu unset BABY_YODAWe can instead turn this into a single command by defining the variable before command: BABY_YODA= "Grogu" bash baby-yoda.shNow you might be wondering what if you want to temporarily expose an environment variable to multiple commands? It may not work the way you would expect. You can use the pstree command (For Mac users: brew install pstree) to visually see this hierarchy in action.
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