concatenating variables

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hello - I'm new to Perl. Trying to set up a loop to call a series of lines to submit to SQL I've already assigned $line1, $line2, $line3 etc with sql queries to run on the database. The problem is perl doesn't seem to like $linename.$counter


my $line1 = "use pricedb;";
my $linename = "line";

my $dbh = DBI->connect("DBI:mysql:host=localhost;database=mysql","root
+","root");


# set up a loop to make submitting lines easier  ;

  for(my $counter = 1; $counter <=10; $counter ++)
      {
       
        my $concatline = $linename.$counter;
        my $rowsaffected = $dbh ->do(${$concatline});
        if ($rowsaffected && $rowsaffected == 0E0)
            {
              print "Operations ws successful but no rows were affecte
+d \n";
            }
        elsif($rowsaffected)
            {
              print "Operation was successful ($rowsaffected rows)\n";
            }
        else
            {
              print "Operation failed: $DBI::errstr\n";
            }
      }
        
   $dbh -> disconnect;
[download]

Please advise how I get the loop to pull $line1, $line2 etc? NB I'm very new to Perl so would appreciate v simple suggestions - my previous experience is SAS, Matlab and a little VBA..Thanks!!

Comment on concatenating variables Download Code

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Re: concatenating variables by brx (Pilgrim) on Jul 31, 2012 at 17:37 UTC
Very quick answer : don't 'forge' variable name. Use an array. If you realy need to 'forge' name, use an hash: `my %names; $names{$linename.$counter} = "use pricedb;" ;` [download] With an array: `#my $line1 = "use pricedb;"; my @lines = ( "use pricedb;" , "..." , "..." , ); for my $counter (1 .. 10) { my $rowsaffected = $dbh ->do($lines[$counter]); #...` [download] Better, without $counter: `for my $line (@lines) { my $rowsaffected = $dbh ->do($line); #...` [download] English is not my mother tongue. Les tongues de ma mère sont "made in France".	[reply] [d/l] [select]
Re^2: concatenating variables by Anonymous Monk on Aug 02, 2012 at 09:01 UTC
Many thanks all - works a treat - problem now solved, and am reading the 'Learning Perl' book... Best wishes..	[reply]
Re: concatenating variables by suaveant (Parson) on Jul 31, 2012 at 17:41 UTC
There are ways to do this but it is generally considered bad practice to do so unless you have no other choice. Consider instead an array. `$lines[0] = "use pricedb"; $lines[1] = "second statement"; for my $sql (@lines) { $dbh->do($sql); # check code here }` [download] That easily lends itself to pulling queries from a file or building queries programmatically. It also means you can have an arbitrary number of lines. I highly suggest getting Learning Perl And/Or The Camel Book If you are going to be doing any amount of Perl programming, both are very useful. Of course there are lots of online tutorials, too. - Ant - Some of my best work - (1 2 3)	[reply] [d/l]
Re: concatenating variables by Khen1950fx (Canon) on Jul 31, 2012 at 21:18 UTC
Primarily to test the efficacy of `join`, I tried it sans DBI, joining `$linename` and `$counter`. I used `$i` instead of $counter. `#!/usr/bin/perl use autodie; use strictures 1; use Time::HiRes qw/sleep/; my $linename = 'line'; my $rowsaffected = 0; my $i = 1; my $max = 10; foreach $_ ( 1 .. $max ) { my $concatline = ( join( '', $linename, $i ) ); ++$concatline; sleep(0.01); if ( $rowsaffected == 0 ) { print "Operations were successful but no rows were affected"; } elsif ($rowsaffected) { print "Operation was successful ($rowsaffected rows)n"; } else { print "Operation failed: $!"; } } exit 0;` [download]	[reply] [d/l] [select]
Re^2: concatenating variables by Anonymous Monk on Aug 01, 2012 at 01:25 UTC
Primarily to test the efficacy of join .. Stop trolling !	[reply]
Re: concatenating variables by DStaal (Chaplain) on Aug 01, 2012 at 20:16 UTC
While you can probably do what you are trying to do, I strongly suspect you can get what you need with DBI placeholders/bind values, which will be a lot safer and clearer. (And, depending on the database, faster as well.) See the DBI man page for more information.	[reply]