Question

Often in Perl I want to print out column/row data, say, from a hash.

This is simple:

foreach my $k(keys %h)
{
  print $k, "	", $h{$k}, "
";
}

However, if the key happens to have a varying length, then the formatting just looks very jagged. I ve investigated format, and it s typically too heavyweight for what I m looking for, which is a simple column-row aligning pretty-printer.

Answer 1

I think you ll find printf useful. Here is a small example:

printf("%10s	%10s
", $k, $h{$k});
## prints "         key	         value
"
## prints "  longer_key	  longer_value
"

Long values are not truncated, and you can change text alignment inside the block:

%10s - means string type of length 10 (left aligned)
%-10s - means string type of length 10 (right aligned)

A full list of formats is on the sprintf man page.

Answer 2

Check out the x operator (documented at perldoc perlop), useful for simple formatting tasks that involve padding fields to a specific length:

while ((my $key, $value) = each %h)
{
    print $key . (" " x (20 - length $key)) . $value, "
";
}

You can also use sprintf or printf (perldoc -f sprintf, perldoc -f printf) (with these you can also pad with zeros in numbers):

while ((my $key, $value) = each %h)
{
    printf("%20s %20s
", $key, $value);
}

Answer 3

The robust solution requires two passes: one to determine the length of the longest key, the other to print the output:

my $l = 0;
foreach my $key (keys %hash) {
    $l = length($key) if length($key) > $l;
}

foreach my $key (keys %hash) {
    printf "%-${l}s  %s
", $key, $hash{$key};
}

If you know the upper limit of the key lengths ahead of time, you can avoid the first loop.

Answer 4

If you want a heavy-duty solution, there are modules like Text::Table.

Answer 5

It is probably not an optimal solution, but you ll need to find your maximum key and maximum value lengths, and then pass them to either sprintf() or pack().

Or you could use static maximum lengths if your data source has "reasonable" constraints (for example, column length limits in a database, etc.)

Answer 6

I know you said format might be too heavy-weight, but it might actually be less complex. Try something like this:

foreach my $k(keys %h) {
  format =
  Key:  @<<<<<<<<<<<<<<<< Value:  @>>>>>>>>>>>>>>>>>
  $k,                     $h{$k}
  .

  write;
}

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