Control Structures

If and Unless

• The if statement evaluates a control expression for truth.
• If the control expression evaluates to true, the associated control structure is executed. Otherwise, the control structure is skipped.
• An elsif statement can specify an alternate control expression and control structure for evaluation and possible execution.
• An else statement can specify an alternate control structure for execution if no other control expressions were true.
• Example:
  

  if ( expression ) { 
      some_statement; 
      some_statement; 
      some_statement; 
  } elsif ( another_expression ) { 
      some_statement; 
      some_statement; 
  } elsif ( another_expression ) { 
      some_statement; 
      some_statement; 
  } else { 
      some_statement; 
      some_statement; 
  }
  

• The unless statement can be used if you wish to have only an else clause with no if clause. This can be helpfull for error messages or logging.
• Example:
  

  unless ( expression ) { 
      some_statement; 
      some_statement; 
      some_statement; 
  }
  

• The unless statement can also have an else.