Printing only on a match

[Diamond, Mark]

This post is prompted by having my earlier mistake ("Preventing lines from
printing 23/8/09) pointed out to me. My problem is now one of elegance
rather than failure.

I have

while (<>) {
..
..
($angle, $stage)= /^(\d\d)(\d+)/;
print "$angle $stage\n";
..
..
}

which prints something whether there is a match or not. I assume that I can
avoid the printing when there is no match by comparing $angle and $stage
with null strings, but please, what is the/a sensible/elegant way of
printing on a complete match and not printing on no match or only a partial
match?

Cheers,
Mark

 

[Jens Thoms Toerring]

This post is prompted by having my earlier mistake ("Preventing lines from
printing 23/8/09) pointed out to me. My problem is now one of elegance
rather than failure.

I have

while (<>) {
.
.
($angle, $stage)= /^(\d\d)(\d+)/;
print "$angle $stage\n";
.
.
}

which prints something whether there is a match or not. I assume that I can
avoid the printing when there is no match by comparing $angle and $stage
with null strings,

i guess you meant by checking if they are defined.

but please, what is the/a sensible/elegant way of
printing on a complete match and not printing on no match or only a partial
match?

The simplest way might be

while (<>) {
print "$1 $2\n" if /^(\d{2})(\d+)/;
}

Don't know if it sensible/elegant enough for your eyes;-)

Regards, Jens

 

[Bart Lateur]

Often, but not always, a sensible way is to add "or next":

while (<>) {
.
.
($angle, $stage)= /^(\d\d)(\d+)/ or next;
print "$angle $stage\n";
.
.
}

This doesn't work outside of a loop, but these situations very typically
appear in loops, so I use it often.

For the general case, you can use the slightly more verbose:

if( my($angle, $stage)= /^(\d\d)(\d+)/ ) {
print "$angle $stage\n";
}

 

[Jürgen Exner]

This post is prompted by having my earlier mistake ("Preventing lines from
printing 23/8/09) pointed out to me. My problem is now one of elegance
rather than failure.

I have

while (<>) {
.
.
($angle, $stage)= /^(\d\d)(\d+)/;
print "$angle $stage\n";
.
.
}

which prints something whether there is a match or not. I assume that I can
avoid the printing when there is no match by comparing $angle and $stage
with null strings, but please, what is the/a sensible/elegant way of
printing on a complete match and not printing on no match or only a partial
match?

Per idiom for that kind of task:

print "$angle $stage\n" if ($angle, $stage)= /^(\d\d)(\d+)/;

jue

 

[Diamond, Mark]

Many thanks to all. My perl code now works correctly and is much easier to
read.

Cheers,
Mark