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Character classes not working in grep command
Seems grep / egrep does not support character classes, e.g.
# find -type f | grep -e '[\d]'
It finds all the file contains the character d, instead of decimal number(s).
Answer:
By default, egrep only understand the POSIX Basic Regular Expressions (BRE) standard, so what would like to use is:
# find -type f | grep -e '[[:digit:]]'
or you can force to interpret as a Perl regular expression
# find -type f | grep -P -e '[\d]'
eq vs == in Perl
Answer:
1. eq
It perform string comparison.
my $foo = "123";
my $bar = "123";
print $foo eq $bar; # output "1"
2. ==
It perform numeric comparison, string is first converted to numeric value before compare.
my $foo = "foo";
my $bar = "bar";
print $foo == $bar; # output "1", since 0 = 0 as strings are converted to 0 in both variables
Difference between die and exit in Perl?
Answer:
The main differences:
How to find out whether reference is pointing to a scalar, array or hash in Perl?
Answer:
Use the ref() function
my $data = [1,2,3];
print ref($data); # print out ARRAY
How to remove install CPAN modules?
Answer:
1. Copy the script below, e.g. remove_module.pl
#!/usr/bin/perl -w
use ExtUtils::Packlist;
use ExtUtils::Installed;
$ARGV[0] or die "Usage: $0 Module::Name\n";
my $module = $ARGV[0];
my $inst = ExtUtils::Installed->new();
foreach my $item (sort($inst->files($module))) {
print "Removing $item\n";
unlink $item;
}
my $packfile = $inst->packlist($module)->packlist_file();
print "Removing $packfile\n";
unlink $packfile;
2. Execute the script to remove module, e.g. MongoDB
# perl remove_module.pl MondoDB
