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Directing output to a file

From: Unix for Mac OS X Users

Video: Directing output to a file

In the last movie I told you that the standard output in Unix is going to be to the screen and we can see that. Notice that I'm inside my user directory, inside Unix files and I'm just going to type sort and fruit.txt. This is the command we did before, just sorts this list of fruit. Now I didn't actually change the file itself, all right. Sort just took it and the output of that command was to my screen. Not back to that file. Just simply output it to the screen and that's what we're seeing there. What we want do now is change the output. We want it to go somewhere else.

Directing output to a file

In the last movie I told you that the standard output in Unix is going to be to the screen and we can see that. Notice that I'm inside my user directory, inside Unix files and I'm just going to type sort and fruit.txt. This is the command we did before, just sorts this list of fruit. Now I didn't actually change the file itself, all right. Sort just took it and the output of that command was to my screen. Not back to that file. Just simply output it to the screen and that's what we're seeing there. What we want do now is change the output. We want it to go somewhere else.

The way we do that as we say sort fruit.txt and then after that we use the greater than sign or an arrow pointing to the right. Essentially that's the way we're directing the output and we want to direct it to a filename and the file doesn't have to exist already. We're going to create a new file, sorted_fruit.txt. So that's it. That's all there there is to it. We simply say our instead of sending this information to the screen direct it to sorted fruit.txt. Hit Return, and I don't get any output because the output didn't come to my screen anymore but if I do ls -la we now see that there's this sorted_fruit file and if we take a look at that sorted_fruit file there it is, there is my output.

So extremely useful, especially for something like sort like that. Then we actually have the sorted version of the file and now we can do something like call unique on that file right. Before we saw the unique didn't work unless the results were sorted . Now we have the ability to do that. Now we could save this unique version if we wanted, right. Go ahead and try that your own. Save it to something called unique sorted_fruit. So any command that we typically get output back to the screen we can actually have be directed to a file. So for example let's say "Hello World" right.

echo, and instead echo coming back to me let's put that in the file, right, hello_world.txt. It did it. We did do ls -lah, right. We saw that command before. Normally that returns our directory listing. Let's save that to our file, content.txt. Let's try history. We just saw how to work with history. Do recent history.txt. So you can see when I just do ls -la you can see that all these files have now been created and you could do a cat on any of them and you'd see the content and it's exactly what would've come your screen but now it's going to a file instead.

Let me show you another one. We did the banner command earlier. Let's do banner "Hello World" and let's save that also to hello_world.txt. Now notice we already have an existing file called hello_world.txt, which just contains the text hello world. So what do you think what we'll get when we take a look at that file now? It's very long. Well let's scroll up to the top of it just to show you that it completely replaced what was there, right. It is destructive, so it does overwrite. So you're essentially saying make this output completely take over this file.

All right, we're going to learn how to append to our file in the next movie, to add more content to it. What this does is replaces it, okay. So very important, make sure that you understand that otherwise you might accidentally target a file that you don't mean to. Let me just show you a classic use case for this which is, if we do, let's say we have two files here and I have a file called new file.txt. It just has a couple lines in it, and I have a another version of it called newer_file.txt, right. Different text to that. Notice the lines that are in each one.

Cat you remember concatenates, right. So new_file.txt concatenated with newer_file.txt and let's put the output to joined.txt, okay. So there it is. It outputs those two concatenated together and directed the output to this file called joined. Now if we take a look at joined, you can see that we get both of those together in one file. And as I noted before, of course if we go up and we change the order of those, let's edit this so that we take new and newer and reverse them.

Now if we do cat joined you'll see that it flipped the order of them and replaced the old one. The old one is completely gone. So again it overwrote that one destructively. If we instead want to append the file, to add to it, we need to do something else and that's what we'll see how to do in the next movie.

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This video is part of

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Unix for Mac OS X Users

82 video lessons · 26128 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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