Pipes and Filters

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Pipes and Filters
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Pipes Filters

• You can construct powerful Unix command lines by
  combining several Unix commands.
• Unix commands alone are powerful, but when you
  combine them together, you can accomplish complex
  tasks with ease.

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Using a Pipe

• The symbol is the Unix pipe symbol that is used
  on the command line. It sends the standard output
  of the command to the left of the pipe to the
  standard input of the command to the right of the
  pipe
• This is similar to the gt symbol used to redirect
  the standard output of a command to a file
• However, the pipe is different because it is used
  to pass the output of a command to another
  command, not a file

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Here is an example

• miller.cs cat apple.txtcore worm seed
  jewelmiller.cs cat apple.txt wc 2
  4 21miller.cs
• After the first shell prompt, we see the contents
  of the file apple.txt
• In the next shell prompt, the cat command
  displays the contents of the applex.txt file
• The contents are displayed, not to the screen,
  but through a pipe to the wc (word count) command
• The wc command then does its job and counts the
  lines, words, and characters of its input

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Using a Filter

• A filter is a Unix command that does some
  manipulation of the text of a file
• One of the most commonly used filters is grep

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grep

• search for a string in a a file, display the line
  in which it appears
• miller.cs cat apple.txtcore worm seed
  jewelmiller.cs grep jewel apple.txtseed jewel
• miller.cs cat apple.txt grep jewel seed jewel