Reading a directory Sorting the files

The following post might help the readers to open a directory. skip the current directory . and previous directory .. and considering only the files which needs to be sorted. In files we use Tie::File to tie the records to the file. So whatever we operate on records changes are automatically made to the file.


Sample Function:

use Tie::File;

sub _sort_deployment_files{
my $deploy_dir

opendir(DIR, $deploy_dir);
@files = grep { /^[^\.]/ && -f "$deploy_dir/$_" } readdir(DIR);
closedir DIR;

foreach my $file_name (@files) {
tie my @records, "Tie::File", $file_name, autochomp => 0, mode => O_RDWR;
sort @records;
untie @records;
}

return;
}

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Redirect to /dev/null

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.

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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/\;.*$//;

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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

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Get a date in yyyymmdd format

use POSIX;
my $today = POSIX::strftime('%Y%m%d', localtime);

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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'};

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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.

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