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Complete Idiot's Guide to Linux
(Publisher: Macmillan Computer Publishing)
Author(s): Manuel Ricart
ISBN: 078971826x
Publication Date: 12/22/98

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Viewing a Page at a Time: less

When you use cat, you might have already found out that if the size of the file is more than can fit on your screen, the contents scroll much too fast for you to read. One way of handling this is by using a pager command.

Pagers allow you to view a screenful (or page) of information at a time. There are two commands that you can use: the original pager called more and the better pager less. In the case of these programs, less is actually more. For example, less allows you to “back up” and scroll up something that more doesn’t allow. less also doesn’t quit until you tell it to.

When less prints a screenful, it puts at the bottom of the screen a colon (:). This means that there’s more information after the current page. While the colon is displayed, you can interact with less and send it commands. Here are some of the more useful:

  To scroll forward (or down) another screenful, press the Spacebar
  To scroll backward (or up) a screenful, press B
  To display the current filename you are viewing and information about where you are in the file, press =
  To quit reading, press Q

When you reach the end of the file, less aptly prints “END” at the bottom of the screen; press Q if you would like to exit the program.

Peeking at the First Few Lines: head

Sometimes you don’t want to read an entire file, just the first few lines. The command for this is called head, and it prints the first ten lines in a file:

     [alberto@digital alberto]$ head /etc/passwd
     root:x:0:0:root:/root:/bin/bash
     bin:x:1:1:bin:/bin:
     daemon:x:2:2:daemon:/sbin:
     adm:x:3:4:adm:/var/adm:
     lp:x:4:7:lp:/var/spool/lpd:
     sync:x:5:0:sync:/sbin:/bin/sync
     shutdown:x:6:11:shutdown:/sbin:/sbin/shutdown
     halt:x:7:0:halt:/sbin:/sbin/halt
     mail:x:8:12:mail:/var/spool/mail:
     news:x:9:13:news:/var/spool/news:

If you pass the -n option, you can control how many lines head prints:

     [alberto@digital alberto]$ head -n 1 /etc/passwd
     root:x:0:0:root:/root:/bin/bash

Peeking at the Last Few Lines: tail

The flip side to head is tail. By default it prints the last ten lines. If you supply the -n option, head will print that number of lines from the end of the file:

      [alberto@digital alberto]$ tail -n 1 /etc/passwd
     alberto:x:100:100:Alberto Ricart:/home/alberto:/bin/bash


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