Be careful: what you’ve written isn’t doing what you think it’s doing. Remember, perl has no real boolean datatype. It’s got scalars, hashes, lists, and references. The way it handles true/false values, then, is contextual. Everything evaluates to “true” in perl except for undefined variables, the empty list, the empty string, and the number 0. … Read more
Subroutines are stored in a global namespace at compile time. In your example b(); is short hand for main::b();. To limit visibility of a function to a scope you need to assign an anonymous subroutines to a variable. Both named and anonymous subroutines can form closures, but since named subroutines are only compiled once if … Read more
Assignment to a glob *glob = VALUE contains some magic that depends on the type of VALUE (i.e., return value of, say, Scalar::Util::reftype(VALUE)). If VALUE is a reference to a scalar, array, hash, or subroutine, then only that entry in the symbol table will be overwritten. This idiom local *array = shift(); #use @array here … Read more
If you have perl 5.10, use the smart-match operator ~~ print “Exist\n” if $var ~~ @array; It’s almost magic.
NOTE This advice is out of date. Module::Build has been removed from the Perl core but lives on as a CPAN module. The pros and cons still stand, and my opinions about MakeMaker still stand. As the former maintainer of ExtUtils::MakeMaker, I like to recommend Module::Build because MakeMaker is a horror show. Module::Build is so … Read more
The Devel::Peek module is very handy to get all sorts of information about variables. One of the things you can do with it is dump a reference to a subroutine and get the name of the glob it came from: $ perl -MDevel::Peek -MList::Util=first -e’Dump(\&first)’ SV = IV(0x1094e20) at 0x1094e28 REFCNT = 1 FLAGS = … Read more
There seems to be quite a bit of confusion because, depending on what you are trying to accomplish, “the number of days between two dates” can mean at least two different things: The calendar distance between the two dates. The absolute distance between the two dates. As an example and to note the difference, assume … Read more
You can use IPC::Open3 to achieve bi-directional communication with child. use strict; use IPC::Open3; my $pid = open3(\*CHLD_IN, \*CHLD_OUT, \*CHLD_ERR, ‘cat’) or die “open3() failed $!”; my $r; for(my $i=1;$i<10;$i++) { print CHLD_IN “$i\n”; $r = <CHLD_OUT>; print “Got $r from child\n”; }
[The OP is asking about the format of the string returned by a hash in scalar context before Perl 5.26. Since Perl 5.26, a hash in scalar context no longer returns a string in this format, returning the number of elements in the hash instead. If you need the value discussed here, you can use … Read more
Install if missing ExtUtils-MakeMaker module (sudo yum install perl-ExtUtils-MakeMaker) Install Perl DBI module ($ yum install perl-DBI) Manually install below three RPMs for Oracle instant client (from Instant Client Downloads for Linux x86-64. The example is for v11.2.0.3.0-1: adapt the commands below to the actual version.) oracle-instantclient11.2-basic-11.2.0.3.0-1 oracle-instantclient11.2-devel-11.2.0.3.0-1 oracle-instantclient11.2-sqlplus-11.2.0.3.0-1 I am using 64 bit Linux … Read more