Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Write to the middle of a file in Perl
Answer:
To write to the middle of a text file, can be easily performed by Perl.
Assume the file has 10 lines, you want to replace the 5th line:
#!/usr/bin/perl
use strict;
use Tie::File;
my $file = 'foo.txt';
tie @array, 'Tie::File', $file or die "Cannot open $file \n";
@array[4] = "Replaced!\n";
That's easy?
What are PHP variable variables?
Answer:
A variable variable takes the value of a variable and treats that as the name of a variable.
Example:
<?php
$foo = "bar";
$bar = "foo";
echo $foo; // print "bar"
echo $$foo; // print "foo", since $foo = "bar", thus $$foo = $bar
Reference: http://il2.php.net/manual/en/language.variables.variable.php
Is PHP pass by reference or pass by value?
Answer:
PHP is pass by value, see the code below:
<?php
class Dog {
public $name;
public function __construct($name) {
$this->name = $name;
}
}
function bar($dog) {
$dog = new Dog("bar");
echo $dog->name;
}
$d = new Dog("foo");
echo $d->name;
bar($d);
echo $d->name;
If PHP is pass by reference, the last echo statement will print out "bar" instead of "foo", which is not true.
What is the difference between || and or in Perl?
Answer:
In Perl, sometimes you can use both `||` and `or` to to do the same thing. But the main different is:
Example:
open FILE, $file or die("Cannot open $file"); # Work
open FILE, $file || die("Cannot open $file"); # Does not work , because it it same as the next statement
open FILE, ($file || die("Cannot open $file")); # Obviously not work
Pass hash as reference in Perl
Answer:
In the previous post, we talked about how to Pass hash as list in Perl, now we discuss another way: To pass a hash as a reference in Perl function.
sub foo {
my ($h) = @_;
print $h->{"1"};
}
foo ( {"1" => "One", "2" => "Two"} );
One will be printed out.
