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Setting the PATH variable

From: Unix for Mac OS X Users

Video: Setting the PATH variable

We first took a look at the path variable back in Chapter 5. You can jump back there if you need a quick refresher. Path is a colon delimited list of file paths that Unix uses when it's trying to locate a command that you want it to run. And we can take a look at that with echo $PATH. There you see each of the paths that it's going to check in. For example, /usr/bin and then a colon followed by the next path /bin and then a colon and so on down the line. And Unix will look in each of those directories, trying to locate a command in that order. So for example, if we type less unix_ files/lorem_ipsum.txt, then the process that Unix went through when trying to run the LESS command was to first look for it in this directory and then if it didn't find it, to look for it in this directory, and so on all the way down the line.

Setting the PATH variable

We first took a look at the path variable back in Chapter 5. You can jump back there if you need a quick refresher. Path is a colon delimited list of file paths that Unix uses when it's trying to locate a command that you want it to run. And we can take a look at that with echo $PATH. There you see each of the paths that it's going to check in. For example, /usr/bin and then a colon followed by the next path /bin and then a colon and so on down the line. And Unix will look in each of those directories, trying to locate a command in that order. So for example, if we type less unix_ files/lorem_ipsum.txt, then the process that Unix went through when trying to run the LESS command was to first look for it in this directory and then if it didn't find it, to look for it in this directory, and so on all the way down the line.

In this movie I want to still learn to modify our path variable using what we just learned in the last movie about setting environment variables. To begin with, let's just do it here from the command line. PATH= and we'll just use an empty string. So now we're telling it don't look in any directories when trying to find these commands. We're essentially unsetting the path. Now let's try that same command again. less unix_files/lorem_ipsum.txt. It comes and it says "Oops! less? I've never heard of it. I can't find it." Now less is still a functioning program. We didn't disable less.

What we did was we took away Unix's ability to find the command less. We can still run it if we did /usr/bin less and then unix_files/lorem_ipsum.txt, and now it still works. We just had to go ahead and specify the full path to find the command instead of having it built into our path that Unix would automatically use to look for it. So you see what the path does and you also see how you can screw yourself up if you get your path wrong. Now luckily all we have to do is reset this environment variable back to this default string and we will be all set, or as we saw in the last movie we can actually just close our window and reopen a new one, and now echo $PATH will return the original string again, because it wasn't saved between bash sessions.

Now, of course most of the time we probably do want our path variable setting to stick around, so we're going to want to put this in our bashrc file. nano .bashrc, and then in here we can do export PATH= and then whatever we want to set that value to. Obviously, we don't want to unset it, so instead let's just type in the current setting and we can use that as a starting point for making modifications. Now what kind of modifications might you want to make to the path? Well, you might want to take something out of the path. You might say, "Oh you know what? I don't want it to look in this directory anymore.

I want to just take that out of the equation." So you can make that change if you wanted. More often what we want to do is we want to control the order in which the path happens. So for example, a very common one is to say all right, let's take usr/local/bin. I'll actually copy that and use Option to shoot to the beginning of the line here, and we'll want to put that at the beginning. So now it'll look for usr/local/bin before it starts looking in those other directories. That gives me, the user, the opportunity to put a file in there. Maybe I want to run my own version of less, right? So I put my own version in usr/local/ bin and it'll get to my version before it gets to the version that's inside usr/bin.

Now we could do it this way by just declaring a new string for the path, but a more common way to do it is just to amend the existing variable by adding to it. Let me show you how we do that. Let me just use Option and I'll shoot down here to the end. Let me just erase a bit. There we are. And let's just take all of this away, all the way back to here, and then let's use $PATH. So what I am doing is I am calling the existing value of path, which is that string we just had, and I am going to use that inside my new string but put my new path at the beginning, and set that whole thing then equal to my new version of path.

It's no problem to use path both here and here. However, what is a problem is the single quotes. We have to use double quotes whenever we want it to pull in the value of this dollar sign variable. If we just use single quotes then it will take it as a literal string. it'll think we want it to look inside a directory called $PATH, which doesn't exist. What we want is we've to grab that variable, so the double quotes are very important. So we can also put our new code at the end, if we wanted it to look in usr/local/bin, after its normal places. We can put it at the end.

But I want to try and get in front of it. I want to say all right, I am not trying to add to the path to the additional places that you might check. I am trying to supersede whatever is in your additional path. A very common setting to use and one that I use in a lot of my trainings is usr/local/bin: followed by usr/local/ and then sbin and then colon and then if you have MySQL installed, usr/local/mysql/bin. So that's only if you have MySQL installed you want to do that last one but what I am saying is all right, basically checking my three main local directories where I might have put things.

And then if you can't find something there, then go look in all the additional places where you might normally look for commands. Now you may realize that actually usr/ local/bin is defined inside PATH, right? So it's actually going to be in the string twice. That's not a big deal. Don't worry about that. It's really not a major concern that it puts both of those in the path. If you really cared about it, you could put the full string or edit it out somehow. But it's perfectly acceptable to do it this way and just have it in the path twice. Let's use Ctrl+X to exit. we'll save the changes to our bashrc file.

If we just do echo $PATH now, we won't have that value because we have to run the bashrc file again or we have to close our window and open a new one. Now we try echo $PATH and now you can see that it made my changes at the beginning. So here's my directories followed by the regular path. Now at this beginner level it might not be really obvious to you why you would want to do this. But once you start actually working in Unix a lot and you start having your own programs that you start putting in these folders, you'll understand that it's an essential thing to be able to control this path variable.

Probably the most important environment variable that you can set. So it's important that you understand how it works and how to set it.

Show transcript

This video is part of

Image for Unix for Mac OS X Users
Unix for Mac OS X Users

82 video lessons · 25676 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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