basic_linux_commands

Author: Aaron Phalen | Twitter: @aaron_phalen | email: [email protected]

Basic Linux Shell Commands (Ubuntu 12.04)
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1. grep command
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The grep commands allows for search functionality when working with
output strings, files, or directories.

  Examples:
    1. grep "word" file --> Search for all match permutations of word within file.
    2. grep -w "word" file --> Search for exact match of word within file.
    3. grep -r "word" directory --> Search directory recursively for any match of word within file.
    4. grep -i "word" file --> Search case insensitive for all match of word in file.
    5. grep -c "word" file --> Count the number of time the search word was found in file.
    6. grep -n "word" file --> Return line number before output data for found search in file.
    7. egrep "word1|word2" file --> Search for multiple (word1, word2) in file.
    
  Note: It is often useful to use the grep commands when combined with the UNIX
        pipe commands (|) to chain toghether commands.
        
        Examples: 
          (i) cat file | grep -w word --> search for exact word in display contents of a file.
          (ii) ps -ax | grep -i mysql --> search for mysql case insensitive in display process list.
          
2. ps command:
--------------
The ps commands shows processes running on the linux system.  Process may be daemon or not.

  Examples:
    1. ps --> display processes runinng in shell
    2. ps -e --> display processes running as daemon
    3. ps -f --> display proccesses with full options
    4. ps -l --> list more information on processes
    5. ps -ef --> display all processes and daemon on all ttys
    6. ps -a --> display all processes that run on terminal
    7. ps -x --> display all processes that do not run on terminal'
    8. ps aux --> display everything
    
    ps -f 
    
    UID       PID          PPID                 C           STIME               TTY       TIME           CMD
    user id   process id   parent process id    cpu usage   process start time  terminal  command time   command
    
    ps -e 
    
    PID             TTY           STAT        TIME            COMMANDS
    process id      terminal                  process time    commands  
    
    Note: When running the process command for showing daemons, these are not necessarily daemons
          started by the user.  Many daemons are started automatically: nginx, mysql, apache, etc..
    
3. cut commands
The cut command is used to select text from display output

  Example:
    1. cat <filename> --> display file contents 
    2. cut -c2 <filename> --> cut 2nd character of each line of file (index starts at 1)
    3. cut -c1-3 <filename> --> cut characters 1-3 from file
    4. cut -c3- <filename> --> cut characters 3 to end of line in file
    5. cut -c-8 <filename> --> cut characters 1-8 from each line in file
    6. cut -c- <filename> --> cut each line for file
    7. cut -d":" -f1 /etc/psswd --> cut first group from each line in password config delimited by :
    8. grep "bin/bash" /etc/psswd | cut -d":" -f1,6