Important Linux Commands

• chmod – change permission of a file or directory Linux has something called permission on file or folder.
  r – Read permission. Permission to read a file or browse a folder
  w – Write permission. Permission to write to file or create new file in the folder
  x – Execute permission. Permission to execute file
  

  $ls -al
  -rw-r--r--  1 gchandrasa gchandrasa     43 2009-02-15 15:00 sample.txt
  

  the first 3 characters after -, rw- belong to users permission.
  the second 3 characters r-- belong to group permission.
  the third 3 characters r-- belong to others user permission.
  One way to change this permission is using the number
  r = 4
  w = 2
  x = 1
  So if you want to change the sample.txt permission to others, give read and write permissions.
  r = 4 and w = 2, so rw = 4 + 2 = 6
  

  $chmod 646 sample.txt
  

  Give read and write permission to users, read permission to group, and read and write permission to others.
• cd – change directory
  Use this command to change your current directory.
  Example : you need to change directory to Documents

  $ cd Documents

• cp – copy files and directories
  Example : copy file index.php from directory a to directory b

  $ cp a/index.php b/

• ls – list files in a directory
  Example : list files in current directory

  $ ls

  Example : list files in current directory, and show hidden files.
  

  $ ls -a

• man – display manual for a command

  $ man mv

• mkdir – create new directories

  $ mkdir newfolder

• mv – move (rename) files
  Use this command to move your file(s) or to rename file(s).

  $ mv oldfolder newfolder

• rm – remove files or directories.
  Delete all files with extension jpg in current directory.

  $ rm *.jpg

• tar – The GNU version of the tar archiving utility
  Untar and extract file

  $ tar -xvf test.tar.bz2

• unzip – list, test and extract compressed files in a ZIP archive
  Extract file zip

  $ unzip test.zip

  rmdir – remove directory with folders and files
  
  $ rmdir -fr foldername