cheat sheets.

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String#unpack
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Format | Returns | Function
-------+---------+-----------------------------------------
  A    | String  | with trailing nulls and spaces removed  
-------+---------+-----------------------------------------
  a    | String  | string                                  
-------+---------+-----------------------------------------
  B    | String  | extract bits from each character (msb first)
-------+---------+-----------------------------------------    
  b    | String  | extract bits from each character (lsb first)
-------+---------+-----------------------------------------    
  C    | Fixnum  | extract a character as an unsigned integer  
-------+---------+-----------------------------------------    
  c    | Fixnum  | extract a character as an integer           
-------+---------+-----------------------------------------    
  d,D  | Float   | treat sizeof(double) characters as          
       |         | a native double                             
-------+---------+-----------------------------------------    
  E    | Float   | treat sizeof(double) characters as          
       |         | a double in little-endian byte order        
-------+---------+-----------------------------------------    
  e    | Float   | treat sizeof(float) characters as           
       |         | a float in little-endian byte order         
-------+---------+-----------------------------------------    
  f,F  | Float   | treat sizeof(float) characters as           
       |         | a native float                              
-------+---------+-----------------------------------------    
  G    | Float   | treat sizeof(double) characters as          
       |         | a double in network byte order              
-------+---------+-----------------------------------------    
  g    | Float   | treat sizeof(float) characters as a         
       |         | float in network byte order                 
-------+---------+-----------------------------------------    
  H    | String  | extract hex nibbles from each character     
       |         | (most significant first)                    
-------+---------+-----------------------------------------    
  h    | String  | extract hex nibbles from each character     
       |         | (least significant first)                   
-------+---------+-----------------------------------------    
  I    | Integer | treat sizeof(int) (modified by _)           
       |         | successive characters as an unsigned        
       |         | native integer                              
-------+---------+-----------------------------------------    
  i    | Integer | treat sizeof(int) (modified by _)           
       |         | successive characters as a signed           
       |         | native integer                              
-------+---------+-----------------------------------------    
  L    | Integer | treat four (modified by _) successive       
       |         | characters as an unsigned native            
       |         | long integer                                
-------+---------+-----------------------------------------    
  l    | Integer | treat four (modified by _) successive       
       |         | characters as a signed native               
       |         | long integer                                
-------+---------+-----------------------------------------    
  M    | String  | quoted-printable                            
-------+---------+-----------------------------------------    
  m    | String  | base64-encoded                              
-------+---------+-----------------------------------------    
  N    | Integer | treat four characters as an unsigned        
       |         | long in network byte order                  
-------+---------+-----------------------------------------    
  n    | Fixnum  | treat two characters as an unsigned         
       |         | short in network byte order                 
-------+---------+-----------------------------------------    
  P    | String  | treat sizeof(char *) characters as a        
       |         | pointer, and  return \emph{len} characters  
       |         | from the referenced location                
-------+---------+-----------------------------------------    
  p    | String  | treat sizeof(char *) characters as a        
       |         | pointer to a  null-terminated string        
-------+---------+-----------------------------------------    
  Q    | Integer | treat 8 characters as an unsigned           
       |         | quad word (64 bits)                         
-------+---------+-----------------------------------------    
  q    | Integer | treat 8 characters as a signed              
       |         | quad word (64 bits)                         
-------+---------+-----------------------------------------    
  S    | Fixnum  | treat two (different if _ used)             
       |         | successive characters as an unsigned        
       |         | short in native byte order                  
-------+---------+-----------------------------------------
  s    | Fixnum  | Treat two (different if _ used)
       |         | successive characters as a signed short
       |         | in native byte order
-------+---------+-----------------------------------------
  U    | Integer | UTF-8 characters as unsigned integers
-------+---------+-----------------------------------------
  u    | String  | UU-encoded
-------+---------+-----------------------------------------
  V    | Fixnum  | treat four characters as an unsigned
       |         | long in little-endian byte order
-------+---------+-----------------------------------------
  v    | Fixnum  | treat two characters as an unsigned
       |         | short in little-endian byte order
-------+---------+-----------------------------------------
  w    | Integer | BER-compressed integer (see Array.pack)
-------+---------+-----------------------------------------
  X    | ---     | skip backward one character
-------+---------+-----------------------------------------
  x    | ---     | skip forward one character
-------+---------+-----------------------------------------
  Z    | String  | with trailing nulls removed
       |         | upto first null with *
-------+---------+-----------------------------------------
  @    | ---     | skip to the offset given by the
       |         | length argument