LINUX Commands - real world

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  alias    Create an alias   ( ex:  alias ll="ls -al" )
  awk      Find and Replace text, database sort/validate/index
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  bash     GNU Bourne-Again SHell 
  bg       Send to background
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  cal      Display a calendar
  cat      Concatenate and print (display) the content of files
  cd       Change Directory
  chmod    Change access permissions
  chown    Change file owner and group
  chkconfig System services (runlevel)
  clear    Clear terminal screen
  cmp      Compare two files
  command  Run a command - ignoring shell functions 
  cp       Copy one or more files to another location
  cut      Divide a file into several parts
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  date     Display or change the date & time
  dd       Convert and copy a file, write disk headers, boot records
  df       Display free disk space
  diff     Display the differences between two files
  dmesg    Print kernel & driver messages 
  du       Estimate file space usage
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  echo     Display message on screen 
  eject    Eject removable media
  env      Environment variables
  exit     Exit the shell
  export   Set an environment variable
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  fdisk    Partition table manipulator for Linux
  fg       Send job to foreground 
  file     Determine file type
  find     Search for files that meet a desired criteria
  free     Display memory usage
  fsck     File system consistency check and repair
  fuser    Identify/kill the process that is accessing a file
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  grep     Search file(s) for lines that match a given pattern
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  head     Output the first part of file(s)
  history  Command History
  hostname Print or set system name
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  ifconfig Configure a network interface
  ifdown   Stop a network interface 
  ifup     Start a network interface up
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  jobs     List active jobs 
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  kill     Stop a process from running
  killall  Kill processes by name
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  less     Display output one screen at a time
  ln -s    Create a symbolic link to a file
  locate   Find files
  ls       List information about file(s) (ls -al)
  lsof     List open files
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  man      Help manual
  mkdir    Create new folder(s)
  more     Display output one screen at a time
  mount    Mount a file system
  mv       Move or rename files or directories
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  netstat  Networking information
  nice     Set the priority of a command or job
  nohup    Run a command immune to hangups
  nslookup Query Internet name servers interactively
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o
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  passwd   Modify a user password
  ping     Test a network connection
  ps       Process status
  pwd      Print Working Directory
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  read     Read a line from standard input 
  reboot   Reboot the system
  rm       Remove files
  rsync    Remote file copy (Synchronize file trees)
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  scp      Secure copy (remote file copy)
  sed      Stream Editor
  shutdown Shutdown or restart linux
  sleep    Delay for a specified time
  sort     Sort text files
  ssh      Secure Shell client (remote login program)
  su       Substitute user identity
  sudo     Execute a command as another user
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  tail     Output the last part of file
  tar      Store, list or extract files in an archive
  tee      Redirect output to multiple files
  test     Evaluate a conditional expression
  time     Measure Program running time
  touch    Change file timestamps
  top      List processes running on the system
  traceroute Trace Route to Host
  tr       Translate, squeeze, and/or delete characters
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  ulimit   Limit user resources 
  umask    Users file creation mask
  umount   Unmount a device
  unalias  Remove an alias 
  uname    Print system information
  uniq     Uniquify files
  uptime   Show uptime
  useradd  Create new user account
  userdel  Delete a user account
  usermod  Modify user account
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  vi       Text Editor
  vmstat   Report virtual memory statistics
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  wc       Print byte, word, and line counts
  whereis  Search the user's $path, man pages and source files for a program
  which    Search the user's $path for a program file
  while    Execute commands
  who      Print all usernames currently logged in
  whoami   Print the current user id and name (`id -un')
  wget     Retrieve web pages or files via HTTP, HTTPS or FTP
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  xargs    Execute utility, passing constructed argument list(s)
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  zip      Package and compress (archive) files.
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  .        Run a command script in the current shell
  !!       Run the last command again
  ###      Comment / Remark
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