Writing subroutine to log file in perl - perl

Question

I am new to perl scripting. I want to write subroutine test to log file.
for e.g.
my ($logfile, $logpath);
$logpath = '/usr/bin';
$logfile = "$logpath/log.txt";
open (LOG,">>","$logfile") || die ("Error : can't open log file");
sub test
{
print "Hi\n";
my $date = `date`;
}
sub logFunc
{
print LOG "Writing log files\n";
print LOG test(); # we cannot do like this :)
}
logFunc();
Say their are 15+ subroutines. So to write commands in each subroutine to log file I have to write print LOG "[Command]\n"; which works fine but script length is huge. So using common subroutine is their any way to achieve this?

Answer 1

There are several problems with your code.
Are you sure you have (and want) write-access to /usr/bin/?
You don't ever call your log() or your test() subroutines. No one will call any of them automatically.
The name log clashes with the built-in log function. So you will either have to call it with a prepended ampersand &log() which is ugly or rename it.
Your test() sub only has an implicit return value. Rather return the value of $date explicitly.
You are using the deprecated 2-argument version of open using a bare-word global file handle. Please use the 3-arg version with a lexical filehandle: open my $log_fh, '>>', $logfile.

Answer 2

A few hints:
Always add use strict; and use warnings; at the top of your script.
Since you're dealing with reading and writing files, you should also add use autodie;. This will automatically kill your program if you cannot open a file, or you cannot write to an open file.
Don't use OS commands when Perl probably can do exactly what you want without calling an OS command.
A Subroutine usually takes arguments and returns a value of some sort. In your case, have your test subroutine return something to write to the log. Or, create just a log subroutine that writes to a log, and have your test subroutine call it.
Here I'm reversing your subroutine calls. I create a write_to_log subroutine to handle my subroutine calls. My write_to_log adds the date/time stamp and writes that and my message. My various subroutines now just call write_to_log for me.
Notice all of my subroutines return some sort of value. The say command (as well as print) returns a non-zero value on success and a 0 on failure. I can use this to test whether my call to my subroutine worked or not.
use strict;
use warnings;
use autodie;
use features qw(say); #Allows you to use `say` instead of `print:
my $log_file = "/usr/bin/log.txt"; #You have write permission to this directory?
open my $log_fh, ">", $log_file;
my test ( $log_fh ) or die qq(Can't write to the log); #Pass the file handle to log
my test2 ( $log_fh ) or die qq(Can't write to the log);
close $log_fh;
sub test {
return write_to_log ( $log_fh, "Hello World!" );
}
sub test2 {
return write_to_log ( $log_fh, "Goodbye World!" );
}
sub write_to_log {
my $file_handle = shift;
my $message = shift;
use Time::Piece;
my $time = localtime->cdate;
return say {$file_handle} "$time: $message";
}
Here's a webpage that lists good books for learning modern Perl and what to look for in those books. If you're beginning to learn Perl, use one of these books.