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====== Intermediate Unix Commands ======

This page contains just a teaser of some helpful commands.  You should use ''man'' or search for more information about the commands, e.g., what arguments and flags you can use to customize the command.
===== Permissions =====

UNIX organizes permissions by user, group, and others.  There are three different permissions available: read, write, and execute

''chmod'' is the command to change permissions

==== Groups ====

To change the group associated with a file, use ''chgrp''


===== Finding Content: grep =====

Gnu Regular Expression Print (''grep'') is a helpful tool to search for text within files, using--you guessed it--regular expressions!  Regular expressions can be quite simple.

Example: I want to find all the names that start with "Sara" in a file of names

  grep Sara names.txt
===== Finding Files: find =====

You can find files with various characteristics using the ''find'' command.  It will look in the directory specified and all of its subdirectories.  You can then apply a command to those found files.

Examples:

Find all of the files with the .txt extension in the current directory and its subdirectories

  find . -name "*.txt"
  
Find all of the files in my home directory (and its subdirectories) that have no data in them (have 0 Bytes of data)

  find ~ -size 0
  
View all of the information (e.g., last modified date) of all of the files in my home directory (and its subdirectories) that have no data in them 

  find ~ -size 0 -exec ls -l {} \;
===== Finding Differences Between Files: diff =====

===== Beginning of Files: head =====

Usage: 

  head <filename>

shows the first few lines of a file.  You can use a flag to change how many lines are displayed
===== End of Files: tail =====

===== Viewing Services Listening on a Port =====

  lsof -i :<port>

e.g., 

  lsof -i :8080