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Introduction to the Terminal

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Viewing Files With "less"

2:51 with Jay McGavren

In this stage, we're going to introduce some helpful commands you can run in the terminal. We'll start with the "less" command, which is a convenient way to look at the contents of files.

  • Let me change to the ~/workspace/library/non-fiction directory: cd ~/workspace/library/non-fiction
  • ls
  • I have a text file here, called terminal.txt.
  • It's not huge, but it's bigger than the text files we've looked at so far. It contains more that a terminal screen's worth of text.
  • If I want to look at its contents, I could use the cat command: cat terminal.txt
    • But there's a couple problems with this.
    • First, the text doesn't all fit on the screen. The top part is cut off.
    • Second, it leaves the file contents sitting in my terminal output. I can't see my previous commands or their output any more.
    • This file's still pretty short, so it isn't too bad, but with bigger files this could be a real issue.
  • This is why pager programs were created. They're interactive programs that display a file on your terminal screen, one page at a time.
    • When I say they're interactive, I mean that they don't finish running immediately; they wait for input from you.
  • The original pager on most Unix-like systems is a program called more.
    • In fact, it's still around on many systems today.
    • You type the more command name, and pass the names of one or more files you want to read as arguments: more terminal.txt
    • Notice the "More" indicator at the bottom of the screen. It's showing that there's more content in the file that isn't displayed yet.
    • If I press the spacebar, it will display another terminal screenful, or "page", of text.
    • It will keep doing this until it reaches the bottom of the file, at which point it will quit, leaving the file contents displayed on the terminal.
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor
incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu
fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
--More--(30%)
  • Many systems have another, newer pager program installed that's inspired by more, called less.
    • It works in the same way. You type less, followed by the names of one or more files you want to view: less terminal.txt
    • less starts by showing the top of the file.
    • You can use the space bar to show additional pages, if you want, but you can also use the arrow keys to scroll up and down, one line at a time.
    • Unlike more, less does not automatically quit when you reach the bottom of the file, because that would prevent you from scrolling back up.
    • When you want to quit less, you press the "q" key.
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor
incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu
fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in
terminal.txt
  • Notice that unlike more, less doesn't leave the file contents up on your terminal screen when it's done. It restores everything just the way it was.
    • This lets you easily review your previous commands and their output.

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    [MUSIC] 0:00
    In this stage, 0:04
    we're going to introduce some helpful commands you can run in the terminal. 0:05
    We'll start with the less command, 0:09
    which is a convenient way to look at the contents of files. 0:11
    Let me change to the workspace/ library/non-fiction directory. 0:15
    I have a text file here called terminal.text. 0:22
    It's not huge, but it's bigger than the text files we've looked at so far. 0:25
    It contains more than a terminal screen's worth of text. 0:30
    If I wanna look at its contents, I could use the cat command cat terminal.txt. 0:33
    But there's a couple of problems with this. 0:39
    First, the text doesn't all fit on the screen. 0:41
    The top part is cut off. 0:43
    Second, it leaves the file contents sitting in my terminal output. 0:45
    I can't see my previous commands or their output anymore. 0:49
    This file's still pretty short, so it isn't too bad. 0:53
    But with bigger files, this could be a real issue. 0:56
    This is why pager programs were created. 0:59
    They're interactive programs that display a file on your terminal screen 1:01
    one page at a time. 1:05
    When I say they're interactive, I mean they don't finish running immediately. 1:07
    They wait for input from you. 1:11
    The original pager on most Unix-like systems is a program called More. 1:13
    In fact, it's still around on many systems today. 1:18
    You type the more command name and pass the names of one or 1:22
    more files you want to read as arguments. 1:25
    More terminal.txt. 1:27
    Notice the More indicator at the bottom of the screen, 1:30
    it's showing that there's more content in the file that isn't displayed yet. 1:33
    This is the indicator that gives the More program its name. 1:36
    If I press the space bar it will display another terminal screenful or 1:40
    page of text. 1:45
    It will keep doing this until it reaches the bottom of the file, 1:46
    at which point it will quit, leaving the file contents displayed on the terminal. 1:49
    Many systems have another pager program installed that's inspired by More, 1:54
    called Less. 1:59
    It works in the same way. 2:00
    You type less followed by the names of one or more files you want to view. 2:02
    So, less terminal.text. 2:06
    Less starts by showing the top of the file. 2:07
    You can use the space bar to show additional pages if you want, but 2:11
    you can also use the arrow keys to scroll up and down, one line at a time. 2:14
    Unlike More, Less does not automatically quit when you reach the bottom of the file 2:20
    because that would prevent you from scrolling back up. 2:24
    When you want to quit Less you press the Q key. 2:27
    Notice that unlike More, 2:30
    Less doesn't leave the file contents up on your terminal screen when it's done. 2:31
    It restores everything just the way it was. 2:35
    This lets you easily review your previous commands and their output. 2:37
    The cat program is still occasionally useful especially with short files, but now you 2:41
    know a better way to review the contents of larger files, the Less program. 2:46

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