Hello geofflh, and welcome to the Monastery!

Here’s another syntax variation you may find useful: including * in the format string of a call to printf (or sprintf):

use strict;
use warnings;

my $w   = 7;
my $str = "abc";
printf ">%*s<\n", $w, $str;
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Output:

17:34 >perl 1790_SoPW.pl
>    abc<

17:34 >
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— the * is replaced by the contents of the next variable in the following list, in this case $w, so the statement is equivalent to printf ">%7s<\n, $str.

Hope that helps,

Use my:

my ($w, $str, $line);
$w = 3; $str = "abc";  $line = sprintf ("%${w}s ", $str);
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You've already got answers to your questions, I just wanted to add: For some more info on strict see also Use strict and warnings. And, in this case, you can parameterize the width of a sprintf format without interpolating into the format string:

my $w = 5;
my $str = "abc";
my $line = sprintf "%*s", $w, $str;
print "<", $line, ">\n";
__END__
<  abc>
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Update: Athanasius beat me to it ;-)

What is the error message that you get when you use strict?

There is no sprint function in Perl, but there is a sprintf function in Perl.

The common approach is to predeclare your variables as lexical variables using the my keyword.

my $w = 3;
my $str = "abc";
my $line = sprintf "%${w}s ", $str; # still has an error
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Not knowing the error you got, after declaring your variable names, you will still get an error that you can't use 3 as a reference while strict is in effect. This is because Perl sees %${w} and interprets it as %{ ${ w }}, trying to interpret the value of $w as a reference. You can circumvent that problem by building your format string piecemeal:

my $line = sprintf "%" . $w . "s ", $str;
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you will still get an error that you can't use 3 as a reference while strict is in effect. This is because Perl sees %${w} and interprets it as %{ ${ w }}, trying to interpret the value of $w as a reference.

Did you test your assumption?

my $w = 5;
my $str = "abc";
my $line = sprintf "%${w}s ", $str;
print "'$line'\n";
__END__
'  abc '
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The format string is %5s with perl 5, version 20, subversion 2 (v5.20.2).

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

No, I didn't test my assumption, but my wonderment about it slowly ceases.

Perl does not interpolate hashes in strings, as it accurately says in perlop:

For constructs that do interpolate, variables beginning with "$" or "@" are interpolated.

use strict;
print "%foo";
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So, my argumentation above is simply wrong as Perl will not go looking for a hash (reference).