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() [] {} or <> ?

Posted by admin (Graham Ellis), 16 January 2003
There are only three types of brackets in the ASCII character set, but in languages like perl you need to group elements together for many more than just three reasons.   So brackets have to mean different things at different times.

The following table shows you various uses of () [] {} and <> in Perl.

Grouping in Perl

() - Round brackets
1. Precedence in expressions
     e.g. $temp = ($other - 32) / 9 * 5;
2. Force list context
     e.g.  ($var) = split /\s+/,$in,2 ;
3. Tagging ("interesting bits") in regular expressions
     e.g.  $ENV{"QUERY_STRING"} =~ /(.*)=(.*)/;

[] - Square brackets
1. An element in a list
     e.g. $table[16]++;
2. Reference to an anonymous list
     e.g. @chinese = (["Soup","Salad","Seaweed"],      ["Curry","Kung Po","Chow Mein"]);
3. A list slice
     e.g. @start = @info[0..3];
4. Regular expression - any one of
     e.g. /^[A-Za-z]+$/;

{} - curly braces
1. An element in a hash
     e.g. $name = $table{"name"};
2. A block of code
     e.g.  { $i = 16;  $k = 25; }
3. Delimiting a variable name
     e.g.  print ("It weighs ${pounds}lbs\n");
4. general counts in regular expressions
     e.g. /\.\w{2,6}$/;

<> - less than / greater than
1. Read from a file handles
     e.g. @lines = <FH>;
2. Read from matching file names
     e.g. @files = <*.html>;

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