Grep, pipes, filters, top, redirection and append

Learning outcomes:

• Demonstrate the use of grep to filter a text file
• Use redirection (or append) in a command and explain what is happening
• Show the use of head, tail and diff

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• Grep
• grep is a command to filter lines that contain specific text
• Examples
• cat /etc/passwd
• cat /etc/passwd | grep Jane
• cat /etc/passwd | grep Jane |wc -l
• cat /etc/passwd | grep -v Jane
• Redirect and append
• Redirect >
• Append >>
• What's the difference? Redirect erases the file contents, append puts the results at the end of the file
• Display file options
• cat Used to display a file
• Alternatives head, tail and od
• head displays top (default 10) lines
• tail displays end (defaults to 10) lines
• od displays any file by showing hex code
• File comparison
• Use diff to compare files
• By default the output is designed to be read by computer not human
• diff command with examples
• Tar
• What is a tarball? It means tape archive
• Why are the used? To archive files, so they can be easily moved around and worked with
• How do you use one?

  tar -cvf ~/name.tar /home/user/directory

• Gzip is also used to compress into a gzip instead of archive. To use add z to the options (-cvzf) also change the extension to .tar.gz or .tgz

Suggested Activities and Discussion Topics:

• Follow along with me on This video on how to use tar

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