Perl in a Nutshell, 2nd Edition

Statements

A simple statement is an expression evaluated for its side effects. Every simple statement must end in a semicolon, unless it is the final statement in a block.

A sequence of statements that defines a scope is called a block. Generally, a block is delimited by braces, or { }. Compound statements are built out of expressions and blocks. A conditional expression is evaluated to determine whether a statement block will be executed. Compound statements are defined in terms of blocks, not statements, which means that braces are required.

Any block can be given a label. Labels are identifiers that follow the variable-naming rules (i.e., they begin with a letter or underscore and can contain alphanumerics and underscores). They are placed just before the block and are followed by a colon, such as SOMELABEL here:

SOMELABEL: {
  ...statements...
  }

By convention, labels are all uppercase, so as not to conflict with reserved words. Labels are used with the loop control commands next, last, and redo to alter the flow of execution in your programs.