Section 4.10. Heredoc Indentation

4.10. Heredoc Indentation

Use a "theredoc" when a heredoc would compromise your indentation.

Of course, even if your lines are all simple strings, the problem with using a heredoc in the middle of code is that its contents must be left-justified, regardless of the indentation level of the code it's in:

     if ($usage_error) {         warn <<'END_USAGE';     Usage: qdump <file> [-full] [-o] [-beans]     Options:         -full  : produce a full dump         -o     : dump in octal         -beans : source is Java     END_USAGE     }

A better practice is to factor out any such heredoc into a predefined constant or a subroutine (a "theredoc"):

      use Readonly;     Readonly my $USAGE => <<'END_USAGE';     Usage: qdump file [-full] [-o] [-beans]     Options:         -full  : produce a full dump         -o     : dump in octal         -beans : source is Java     END_USAGE     
# and later...
     if ($usage_error) {         warn $USAGE;     }

If the heredoc needs to interpolate variables whose values are not known at compile time, use a subroutine instead, and parameterize the variables:

      sub build_usage {         my ($prog_name, $filename) = @_;         return <<"END_USAGE";     Usage: $prog_name $filename [-full] [-o] [-beans]     Options:         -full  : produce a full dump         -o     : dump in octal         -beans : source is Java     END_USAGE     }     
# and later...
     if ($usage_error) {         warn build_usage($PROGRAM_NAME, $requested_file);     }

The heredoc does compromise the indentation of the subroutine, but that's now a small and isolated section of the code, so it doesn't significantly impair the overall readability of your program.