PERL Miscellaneous - Use of the => operator

Author

Use of the => operator

niall.macpherson@ntlworld.com

2006-03-29, 4:00 am

I needed a bit of code to convert a string to the hex values for the
individual chars and found the following 2 examples

my $teststr = 'abcABC123XYZ';

my $hexstr = join (' ', map (sprintf("%2.2x", ord($_)), split(//,
$teststr))); ## method 1

$hexstr = unpack 'H* ' => $teststr; ## method 2

Both of these work fine , although the second one doesn't separate the
values with spaces (which I needed) so I did

$hexstr =~ s/(\d\d)/$1 /g;

Method 1 was a useful exercise in understanding how map works (which I
previously hadn't been too comfortable with), but I decided to go with
method 2 as it looks a bit cleaner.

I think I understand how unpack works , however I have only previously
seen the => operator used in initialising hashes and I am not clear how
it works in this context. I looked at perldoc perlop but couldn't spot
anything relevant.

I'm therefore unsure how I can insert the spaces in method 2 in the
same line because I don't understand how / why the => operator is used
here.

Can someone please explain ?

Thanks

niall.macpherson@ntlworld.com

2006-03-29, 7:59 am

niall.macpherson@ntlworld.com wrote:

> $hexstr =~ s/(\d\d)/$1 /g;
>

This should of course be

$hexstr =~ s/([0-9A-Fa-f][0-9A-Fa-f])/$1 /g;

Anno Siegel

2006-03-29, 7:59 am

<niall.macpherson@ntlworld.com> wrote in comp.lang.perl.misc:
> I needed a bit of code to convert a string to the hex values for the
> individual chars and found the following 2 examples
>
>
> my $teststr = 'abcABC123XYZ';
>
> my $hexstr = join (' ', map (sprintf("%2.2x", ord($_)), split(//,
> $teststr))); ## method 1
>
> $hexstr = unpack 'H* ' => $teststr; ## method 2

[...]

> I think I understand how unpack works , however I have only previously
> seen the => operator used in initialising hashes and I am not clear how
> it works in this context. I looked at perldoc perlop but couldn't spot
> anything relevant.

Look for "comma operator" in perlop.

As used above, "=>" is entirely equivalent to a comma.

Anno
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Dr.Ruud

2006-03-29, 7:59 am

niall.macpherson@ntlworld.com schreef:

> $hexstr =~ s/([0-9A-Fa-f][0-9A-Fa-f])/$1 /g;

Alternatives for [0-9A-Fa-f]

(?i:[0-9a-f])

[[:xdigit:]]

--
Affijn, Ruud

"Gewoon is een tijger."
echo 014C8A26C5DB87DBE85A93DBF |perl -pe 'tr/0-9A-F/JunkshoP cartel,/'

Tad McClellan

2006-03-29, 7:00 pm

niall.macpherson@ntlworld.com <niall.macpherson@ntlworld.com> wrote:

> $hexstr = unpack 'H* ' => $teststr; ## method 2

> I have only previously
> seen the => operator used in initialising hashes and I am not clear how
> it works in this context. I looked at perldoc perlop but couldn't spot
> anything relevant.

See the "Comma Operator" section.

> I'm therefore unsure how I can insert the spaces in method 2 in the
> same line

Use unpack() in a list context instead of in a scalar context,
then join up the list elements the way you want them:

$hexstr = join ' ', unpack('H* ' => $teststr); # untested

> because I don't understand how / why the => operator is used
> here.
>
> Can someone please explain ?

It is just a comma, the same as if you had:

$hexstr = unpack 'H* ' , $teststr; ## method 2

So, it has no relationship to getting the spaces that you want.

--
Tad McClellan SGML consulting
tadmc@augustmail.com Perl programming
Fort Worth, Texas

Dr.Ruud

2006-03-29, 7:00 pm

Tad McClellan schreef:
> niall.macpherson@ntlworld.com wrote:

>
> It is just a comma, the same as if you had:
>
> $hexstr = unpack 'H* ' , $teststr;

See also:

perl -MO=Deparse -e '$hexstr = unpack q{H* } => $teststr'

--
Affijn, Ruud

"Gewoon is een tijger."
echo 014C8A26C5DB87DBE85A93DBF |perl -pe 'tr/0-9A-F/JunkshoP cartel,/'

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