I came across a code snippet like `$ypmatch $host hosts 2>/dev/null` used in one of the perl files I was browsing. Can anyone let me know the significance of redirecting it to /dev/null.
I will post the same when I find it out.
Wednesday, December 3, 2008
Redirect to /dev/null
Cleaning A Perl File With REGEXP
Following are the regular expressions which can be used to clean your file of unwanted material
1) Replace all the spaces with nothing.
s/\s//g;
2) Skip the lines with comments.next if (m/^\#/);
3) skip blank lines
next if (m/^$/);
4) Replace a line in the file which has commented data on a code line.
s/\#.*$//;
5) Replace a line in the file which has data after semicolon
s/\;.*$//;
Wednesday, November 5, 2008
To get current date and time. hh:mm::ss mm/dd/yy
To get the current date and time in the format hh:mm::ss mm/dd/yy and if you are looking for a perl one liner here you go.
perl -e "use POSIX; print strftime qq(%X %x), localtime(time); "
Output is
00:00:51 11/06/08
Thursday, October 30, 2008
How to take a hash slice.
If you want to assign some variables of a hash to an array. i.e you want to take some of the elements from hash based on there keys into a array here is a trick\
my %hash = (one => 'one', two => 'two', three => 'three');
my @array ;
@array = @{$hash}{'one','two'};
If you have a hashref and want to take the values of some keys into an array you can do the following.
my $hashref = {one => 'one', two => 'two', three => 'three'};
my @array ;
@array = @{%$hash}{'one','two'};
Getopt::Long :s option specifier
: s option of getopt::long come very much handy when one is looking for the following requirement
1) If a command line option is passed a paramter it is taken as a value for the given option
i.e perl program -option1 value1
$option1 will take value1.
2) If a command line option is not mentioned then variable remains undefined.
i.e perl program
$option1 will remain undef.
3) If a command line option is mentioned but paramter is not passed, then a empty string will be assigned to $option if :s is used and 0 if :i is used
i.e perl program -option1
$option will be q{}... an empty string.
Please take a look at http://search.cpan.org/dist/Getopt-Long/lib/Getopt/Long.pm for further information.
Wednesday, January 30, 2008
Perl is Compiled or Interpreted?
Everyone knows that there are two types of languages interpreted and compiled. Does anyone know what type of language a perl is? If your instant answer is interpreted, maybe this post will make you think otherwise.
When one runs a perl program, perl actually generates a intermediate code called as the bytecode. Now when perl is finished with bytecode where it usually compiles the whole of a program, it takes over the responsibility of being an interpreter and acts accordingly scanning and processing each line of code. So perl is actually an intermediate language. It is neither a strictly compiled language nor a strictly interpreted one.
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