Control Structures (Part 3)-- Perl Study Notes

Control Structures (Part 3)-- Perl Study Notes

  Operator syntax
    if ($expression)
    {
    ....
    }
    elsif ($expression)
    {
    ...
    }
    else
    {
    ...
    }
   
    unless ($expression)
    {
    ...
    }
   
    while ($expression)
    {
    ...
    }
   
    until ($expression)
    {
    ...
    } 
   
    do
    {
    ...
    }  while ($expression)
   
    do
    {
    ...
    }  until ($expression)
   
    for($initial_exp1;$test_exp;$reinit_exp)
    {
    ...
    } 
   
    foreach $value (@list)
    {
    ...
    } # $value get each element in the @list
   
    foreach (@list)
    {
    ...
    } #$_ get each element in the @list
 
  How to populate true or false in Perl
    a. convert the expression to string
    b. if the string is empty or "0", it returns false else true
    "0" #false
    0 #false
    "00" #true
    undef #false
    1 #true
 
  last: to exit from the loop
  while (something) {
      something;
      something;
      something;
      if (somecondition) {
        somethingorother;
        somethingorother;
        last; # break out of the while loop
        }
      morethings;
      morethings;
  }
  # last comes here 
 
  next: to exit current loop and continue the next round loop
  while (something) {
      something;
      something;
      something;
      if (somecondition) {
        somethingorother;
        somethingorother;
        next; # break out of the while loop
        }
      morethings;
      morethings;
     # next comes here
  }
  
   redo: to jump to the beginning of the current block(without reevaluating the control expression)
   while (somecondition) {
      # redo comes here without evaluate the somecondition
      something;
      something;
      something;
      if (somecondition) {
        somethingorother;
        somethingorother;
        redo; # break out of the while loop
        }
      morethings;
      morethings;

   }   
   The follow is another loop structure without any while/for/foreach/until statement
   {
     startstuff;
     startstuff;
     startstuff;
     if (somecondition) {
     last;
     }
     laterstuff;
     laterstuff;
     laterstuff;
     redo;
    } # this block will be looped until somecondition is true
   
    Pls note that last/next/redo can not be used in the do{}while/until statement
   
    Expression Modifiers
    some_expression if control_expression
    this is equivalent to
    if(control_expression)
    {
    some_expression
    }
   
    exp2 unless exp1; # like : unless(exp1){exp2;}
    exp2 while exp1; #like: while(exp1){exp2;}
    exp2 until exp1; #like: until(exp1){exp2;}
   
    && and || Control Structures
    this && that; # equivalent to that if this
    this || that; # equivalent to that unless this