How can I quote a long string in Perl?

Question

I usually use simple quotes, but sometime I get very long lines which I can't break and also need to use escape characters, so I get something like this:

my $str = "select query_accession,query_tag,hit_accession,hit_tag,significance from summaryTables where query_id = \'$query_id\';"

I know there are various other ways for representing strings in Perl. What would you recommend?

UPDATE Thank you all guys for the SQL-related suggestions. I learn some valuable stuff, but, my question remains (as a general one, regardless of SQL): is there some operator that allows quoting without catching line breaks?

what I do now is something like:

my $str = "123 123 456 sdndfnd sdfdmd " .
 "dfsdjkfs 343489 dfjsdj 3 34kdfsk kd " .
 "fd kd9534 rfg 546 5";

which is quite ugly.

Answer 1

I like here documents, although some people despise them because the terminator has to appear at the beginning of the line despite your indent level.

my $str = <<"SQL";
  SELECT 
    query_accession,
    query_tag,
    hit_accession,
    hit_tag,
    significance
  FROM   
    summaryTables
  WHERE 
    query_id = ?
SQL

Perl v5.26 introduced indented here docs, like Ruby has. This looks almost the same, and if StackOverflow hasn't messed with the formatting, you should see that the final SQL marker is not flush left like the previous example:

my $str = <<~'SQL';
      SELECT 
        query_accession,
        query_tag,
        hit_accession,
        hit_tag,
        significance
      FROM   
        summaryTables
      WHERE 
        query_id = ?
    SQL

I also like formatting my SQL so I can easily see the structure in the statement, but that's a personal style. You might like something different.

Answer 2

No. All of Perl 5's string creation methods know about and include newlines. You can either use the concatenation operator as you did in your question, or abstract away the code needed to fix the problem:

#!/usr/bin/perl

use strict;
use warnings;

sub single_line {
    my @strings = @_;
    for (@strings) {
        s/\s+/ /g;
        s/^\s+|\s+$//g;
    }
    return wantarray ? @strings : $strings[0];
}


my $sql = single_line "
    select query_accession,query_tag,hit_accession,hit_tag,significance
    from summaryTables
    where query_id = ?;
";

print "[$sql]\n";

Answer 3

Look in perlop's Quote-Like Operators. Use qq for double quotes and q for single quotes.