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Setting and exporting environment variables

From: Unix for Mac OS X Users

Video: Setting and exporting environment variables

In this movie we're going to learn more about environment variables which are also known as shell variables. We're going to do that so that we can begin to use environment variables to configure our working environment. We've touched on shell variables already. For example, we saw that we can have echo $SHELL and that will return the default login shell for the current user. The shell variable in this case is called SHELL and it's in all capitals. The dollar sign is actually not part of the shell variable name. The dollar sign is there to serve as an indication to Unix that we want it to return the value that's stored in the shell variable.

Setting and exporting environment variables

In this movie we're going to learn more about environment variables which are also known as shell variables. We're going to do that so that we can begin to use environment variables to configure our working environment. We've touched on shell variables already. For example, we saw that we can have echo $SHELL and that will return the default login shell for the current user. The shell variable in this case is called SHELL and it's in all capitals. The dollar sign is actually not part of the shell variable name. The dollar sign is there to serve as an indication to Unix that we want it to return the value that's stored in the shell variable.

We can also define our own shell variables as well. For example, I can have MYNAME= and then inside quotes put your name. Then I could echo that back the same way. echo $MYNAME, and it returns the value that we've set inside that variable. Notice that I did not use the dollar sign when I set the value of MYNAME. I only use it when I wanted to retrieve the value. Just like the command aliases that we were creating in the last movie, variables that we set during the current bash session will disappear once we log out of that session.

And like aliases if we want those to be defined all the time, well they need to be stored in either our .bash_profile or our .bashrc file. As I said before, I think the .bashrc file is the better choice. So let's put those in there. Notice I am inside my main user directory. Open up that file. You can put it really anywhere in here. I am going to put it right here near the top. So I'll just say MYNAME= and then I'll put in Kevin Skoglund. Now we'll exit. I'll save the file. Now if we first just try echo $MYNAME, we still have it saved from before.

To really test this, what we need to do is actually close this window and open a new one and then we can try it again. echo $MYNAME, and there it is. Now you can see that it's set all the time. Every time we open up a bash session, this variable will be defined for us. So that takes care making it available the bash. But there's one more thing that we need to do. As I've shown it here, MYNAME won't be available to the child processes that bash starts for us. It'll only be available in bash itself. To indicate to bash it should also pass along these variables or export them to other commands, programs, and scripts, well then we need to use the export command.

Let's go up to nano .bashrc again, and then now we can just say export MYNAME. And now bash knows that it also should export it to all of the programs that it runs as well. So every time it launches a program, it'll make this MYNAME variable available as well. Now you can see here I did it in two lines. I set it in one line and then I exported it in the other. You can actually do both in the same line, and I'll show you that in just a moment. Now while it is moderately useful to define your own variables, it's even more useful to use variables to set some configuration options for our Unix environment and the programs that we use.

For example, if you read the man pages for the command less, you'll learn that there's an environment variable that can be used to configure the default settings that less will use when it starts up. So to do that we'll just use export LESS= and then inside quotes we'll put whatever options we want LESS to use. Notice first of all that I also did the exporting and the setting all on one line. Before I did it on two lines. Here I am doing it in one. export LESS= and then we can use options. So we could use the m, the lowercase m. That will give us a medium verbose prompt every time we start up LESS or we could use capital M. That would be the maximum verbose prompt, right, the longest prompt possible.

We can put capital N. That would give us some line numbers. You can go through the man pages for LESS and decide what options you want. I am just going to use the -M option here. So I am going to use Ctrl+X to exit, and I am already exporting it so that means it will be available not just in bash but inside LESS, because LESS is a program that bash starts. If you want you can play with it. You can try taking away the export and you'll see that it doesn't get passed along. Now if we just do right here echo $LESS, we don't have a value. That's because bashrc has not been run since we made that change.

To do that we either need to close the window and reopen it, or we can call source .bashrc. That will actually execute the program. And now if we go up and say echo $LESS again, you see that value is there. Let's test it out. Let's actually call less on inside of our unix_files. We have that lorem_ipsum.txt file. Let's call it on that. And you'll see now I get that maximum verbose prompt at the bottom. So that's the default option being used every time I call less. So this is the way that you do it.

You can interact with different programs that you might run by setting these values, but make sure that you export them so that they're used not just in bash, but actually pushed out to the program that gets launched as well and made available there. In the next couple of movies I want to show you some more useful environment variables that we can set.

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This video is part of

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Unix for Mac OS X Users

82 video lessons · 25625 viewers

Kevin Skoglund
Author

 
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  1. 3m 57s
    1. Introduction
      1m 14s
    2. Using the exercise files
      2m 43s
  2. 32m 2s
    1. What is Unix?
      7m 27s
    2. The terminal application
      4m 23s
    3. Logging in and using the command prompt
      5m 19s
    4. Command structure
      5m 22s
    5. Kernel and shells
      5m 25s
    6. Unix manual pages
      4m 6s
  3. 15m 58s
    1. The working directory
      2m 49s
    2. Listing files and directories
      3m 59s
    3. Moving around the filesystem
      4m 58s
    4. Filesystem organization
      4m 12s
  4. 1h 4m
    1. Naming files
      5m 41s
    2. Creating files
      2m 19s
    3. Unix text editors
      6m 39s
    4. Reading files
      5m 35s
    5. Reading portions of files
      3m 27s
    6. Creating directories
      2m 40s
    7. Moving and renaming files and directories
      8m 32s
    8. Copying files and directories
      3m 7s
    9. Deleting files and directories
      3m 38s
    10. Finder aliases in Unix
      4m 10s
    11. Hard links
      5m 30s
    12. Symbolic links
      6m 36s
    13. Searching for files and directories
      6m 32s
  5. 34m 58s
    1. Who am I?
      4m 3s
    2. Unix groups
      1m 52s
    3. File and directory ownership
      6m 41s
    4. File and directory permissions
      4m 27s
    5. Setting permissions using alpha notation
      6m 49s
    6. Setting permissions using octal notation
      3m 49s
    7. The root user
      1m 57s
    8. sudo and sudoers
      5m 20s
  6. 52m 34s
    1. Command basics
      4m 4s
    2. The PATH variable
      4m 13s
    3. System information commands
      3m 40s
    4. Disk information commands
      6m 8s
    5. Viewing processes
      5m 0s
    6. Monitoring processes
      3m 36s
    7. Stopping processes
      3m 19s
    8. Text file helpers
      6m 50s
    9. Utility programs
      7m 28s
    10. Using the command history
      8m 16s
  7. 20m 39s
    1. Standard input and standard output
      1m 24s
    2. Directing output to a file
      4m 13s
    3. Appending to a file
      2m 44s
    4. Directing input from a file
      5m 28s
    5. Piping output to input
      4m 40s
    6. Suppressing output
      2m 10s
  8. 41m 28s
    1. Profile, login, and resource files
      9m 11s
    2. Setting command aliases
      6m 59s
    3. Setting and exporting environment variables
      4m 54s
    4. Setting the PATH variable
      6m 10s
    5. Configuring history with variables
      6m 17s
    6. Customizing the command prompt
      6m 5s
    7. Logout file
      1m 52s
  9. 1h 25m
    1. grep: Searching for matching expressions
      5m 21s
    2. grep: Multiple files, other input
      4m 28s
    3. grep: Coloring matched text
      2m 57s
    4. Introduction to regular expressions
      3m 22s
    5. Regular expressions: Basic syntax
      3m 19s
    6. Using regular expressions with grep
      5m 20s
    7. tr: Translating characters
      8m 17s
    8. tr: Deleting and squeezing characters
      5m 30s
    9. sed: Stream editor
      7m 45s
    10. sed: Regular expressions and back-references
      7m 8s
    11. cut: Cutting select text portions
      7m 42s
    12. diff: Comparing files
      4m 35s
    13. diff: Alternative formats
      4m 30s
    14. xargs: Passing argument lists to commands
      7m 25s
    15. xargs: Usage examples
      7m 59s
  10. 42m 25s
    1. Finder integration
      4m 45s
    2. Clipboard integration
      5m 5s
    3. Screen capture
      3m 42s
    4. Shut down, reboot, and sleep
      3m 34s
    5. Text to speech
      2m 36s
    6. Spotlight integration: Searching metadata
      3m 41s
    7. Spotlight integration: Metadata attributes
      4m 24s
    8. Using AppleScript
      5m 23s
    9. System configurations: Viewing and setting
      5m 51s
    10. System configurations: Examples
      3m 24s
  11. 1m 26s
    1. Conclusion
      1m 26s

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