Study Perl cookbook

1:Substring Truncation

 

$ Value = substr ($ string, $ offset, $ count );

$ Value = substr ($ string, $ offset );

 

Substr ($ string, $ offset, $ count) = $ newstring;

Substr ($ string, $ offset, $ count, $ newstring );#Equivalent to the previous statement

Substr ($ string, $ offset)= $ Newtail;

In some casesUnpackMore convenient Functions,AlthoughUnpackIs read-only,But it is more efficient.,You can retrieve multiple substrings at a time.

#First5Bytes,Skip3Bytes,Retrieve again2Items8Bytes,Finally, retrieve the remaining

#(Note::Only supportedASCII,Not SupportedUnicode)

($ Leading, $ S1, $ S2, $ trailing) = unpack ("A5 X3 A8 A *", $ data );

 

#Per5Split byte into Arrays

@ Fivers = unpack ("A5" X (length ($ string)/5), $ string );

 

#Split into single-character Arrays

@ Chars= Unpack ("A1" x length ($ string), $ string );

 

 

 

2.Set the Initial Value

 

#Set$ BAssigned$,If$ BNot true,Then$ CAssigned$

$ A = $ B | $ C;

 

#When$ XWhen not true,Set$ YAssigned$ X

$ X | = $ Y;

When 0 ," 0 ", And""Is the valid value of the Variable,Variables can be defined in this way.:

#Set$ BAssigned$,If$ BNot Defined,Then$ CAssigned$

$ A = defined ($ B )? $ B: $ C;

 

#FuturePerlIt supports "new" or defining operators.

$ A = $ B // $ C;

 

 

3.No temporary variable exchange value

 

($ Var1, $ var2) = ($ var2, $ var1 );

 

In fact, we can exchange more than this.2Variable (s). It is very convenient to directly exchange multiple variables.

 

 

4.Conversion of characters and values

 

$ Num= Ord ($ char );

$ Char = CHR ($ num );

To be continue .......