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Feature/new perl regex questions and answers (#186)

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* New questions and spell check (#181)

Added new questions related with KVM, Libvirt and DNF

* Add new perl regex questions and answers

* Add one way to avoid one-liners in regex
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Adrian 2021-11-19 21:36:42 +01:00 committed by GitHub
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@ -5279,7 +5279,82 @@ sub factorial {
### Perl Regex
<details>
<summary>How do you perform regular expresions in Perl?</summary><br><b>
<summary>Check if the word `electroencefalografista` exists in a string</summary><br><b>
```
my $string = "The longest accepted word by RAE is: electroencefalografista";
if ($string =~ /electroencefalografista/) {
print "Match!";
}
```
</b></details>
<details>
<summary>Check if the word `electroencefalografista` does not exists in a string</summary><br><b>
```
my $string = "The longest not accepted word by RAE is: Ciclopentanoperhidrofenantreno";
if ($string !~ /electroencefalografista/) {
print "Does not match!";
}
```
</b></details>
<details>
<summary>Replace the word `amazing`</summary><br><b>
```
my $string = "Perl is amazing!";
$string =~ s/amazing/incredible/;
print $string;
# Perl is incredible!
```
</b></details>
<details>
<summary>Extract `hh:mm:ss` with capturing group `()` in the following datetime</summary><br><b>
```
my $date = "Fri Nov 19 20:09:37 CET 2021";
my @matches = $date =~ /(.*)(\d{2}:\d{2}:\d{2})(.*)/;
print $matches[1];
# Output: 20:09:37
```
</b></details>
<details>
<summary>Extract all the elements that are numbers in an array</summary><br><b>
```
my @array = ('a', 1, 'b', 2, 'c', 3);
my @numbers = grep (/\d/, @array); # Note: \d involves more digits than 0-9
map {print $_ . "\n" } @numbers;
```
</b></details>
<details>
<summary>Print all the linux system users that starts with d or D</summary><br><b>
- With a Perl one liner :D
```
open(my $fh, '<', '/etc/passwd');
my @user_info = <$fh>;
map { print $& . "\n" if $_ =~ /^d([^:]*)/ } @user_info;
close $fh;
```
- Avoiding one-liners
```
foreach my $user_line (@user_info) {
if ($user_line =~ /^d([^:]*)/) {
print $& . "\n";
}
}
```
</b></details>
### Perl Files Handle
@ -5303,7 +5378,7 @@ sub factorial {
# We can use:
# '>' Write (it clears a previous content if exists).
# '>>' Append.
open(my $fh, '>>', 'file_name.ext') or "Error: file can't be opened";
open(my $fh, '>>', 'file_name.ext') or die "Error: file can't be opened";
print $fh "writing text...\n";
close($fh);
```
@ -5313,7 +5388,7 @@ close($fh);
<summary>How can you read a file and print every line?</summary><br><b>
```
open(my $fh, '<', 'file_to_read.ext') or "Error: file can't be opened";
open(my $fh, '<', 'file_to_read.ext') or die "Error: file can't be opened";
my @file = <$fh>;
foreach my $line (@file) {
print $line;
@ -5323,7 +5398,7 @@ foreach my $line (@file) {
We can use the file handle without assigning it to an array:
```
open(my $fh, '<', 'file_to_read.ext') or "Error: file can't be opened";
open(my $fh, '<', 'file_to_read.ext') or die "Error: file can't be opened";
foreach my $line (<$fh>) {
print $line;