I'm attempting to use Perl's gethostnamebyaddr function. The annoying thing is that it returns the entire domain name in scalar format. I want to parse out only the hostname and discard the rest.
I'm using split to divide the domain name into an array and then taking only the first value but this doesn't seem to work.
#!/usr/bin/perl
use Socket;
my $name;
my $hostname;
my #tmpStr;
$name = gethostbyaddr(inet_aton("192.168.2.3"), AF_INET);
print "$name\n";
#tmpStr = split ".", $name;
$hostname = $tmpStr[0];
print "Host name is $hostname\n";
When the above code is executed, I get the following:
dc1-ent.ent.ped.local
Host name is
According to this website the return value is not a string but is rather a scalar value and so my attempt at splitting it doesn't work.
I can't figure out how to convert it to a string before I can split it or parse out the hostname by itself.
The dot character has special meaning for regular expressions in Perl, and the 1st argument to split is a regular expression. You need to escape the dot:
use warnings;
use strict;
my $name = 'dc1-ent.ent.ped.local';
print "$name\n";
my #tmpStr = split /\./, $name;
my $hostname = $tmpStr[0];
print "Host name is $hostname\n";
This outputs:
dc1-ent.ent.ped.local
Host name is dc1-ent
I would write it like this
my $name = gethostbyaddr(inet_aton('192.168.2.3'), AF_INET);
my ($host) = $name =~ /([^.]+)/;
say $host;
Your problem is not related to gethostbyaddr() but by what follows.
Proof:
DB<1> $name = 'dc1-ent.ent.ped.local';
DB<2> #tmpStr = split ".", $name;
DB<3> print #tmpStr;
(nothing printed)
Try instead using split that way:
DB<8> $name = 'dc1-ent.ent.ped.local';
DB<9> #tmpStr = split(/\./, $name);
DB<10> print #tmpStr;
dc1-ententpedlocal
DB<11> print join(' ', #tmpStr);
dc1-ent ent ped local
DB<12> x #tmpStr;
0 'dc1-ent'
1 'ent'
2 'ped'
3 'local'
Or if you absolutely want a string and not a regex, protect the dot also as your string is still parsed as a regular expression (which is why being explicit with / / has its merits, it forces you to remember that some character have special meaning there, like the dot):
DB<1> $name = 'dc1-ent.ent.ped.local';
DB<2> #tmpStr = split('.', $name);
DB<3> print #tmpStr;
DB<4> #tmpStr = split('\.', $name);
DB<5> x #tmpStr
0 'dc1-ent'
1 'ent'
2 'ped'
3 'local'
Related
I would like to search values after a specific word (Current Value = ) in a log file, and makes a string with values.
vcs_output.log: a log file
** Fault injection **
Count = 1533
0: Path = cmp_top.iop.sparc0.exu.alu.byp_alu_rcc_data_e[6]
0: Current value = x
1: Path = cmp_top.iop.sparc0.exu.alu.byp_alu_rs3_data_e[51]
1: Current value = x
2: Path = cmp_top.iop.sparc0.exu.alu.byp_alu_rs1_data_e[3]
2: Current value = 1
3: Path = cmp_top.iop.sparc0.exu.alu.shft_alu_shift_out_e[18]
3: Current value = 0
4: Path = cmp_top.iop.sparc0.exu.alu.byp_alu_rs3_data_e[17]
4: Current value = x
5: Path = cmp_top.iop.sparc0.exu.alu.byp_alu_rs1_data_e[43]
5: Current value = 0
6: Path = cmp_top.iop.sparc0.exu.alu.byp_alu_rcc_data_e[38]
6: Current value = x
7: Path = cmp_top.iop.sparc0.exu.alu.byp_alu_rs2_data_e_l[30]
7: Current value = 1
.
.
.
If I store values after "Current value = ", then x,x,1,0,x,0,x,1. I ultimately save/print them as a string such as xx10x0x1.
Here is my code
code.pl:
#!/usr/bin/perl
use strict;
use warnings;
##### Read input
open ( my $input_fh, '<', 'vcs_output.log' ) or die $!;
chomp ( my #input = <$input_fh> );
my $i=0;
my #arr;
while (#input) {
if (/Current value = /)
$arr[i]= $input; # put the matched value to array
}
}
## make a string from the array using an additional loop
close ( $input_fh );
I think there is a way to make a string in one loop (or even not using a loop). Please advise me to make it. Any suggestion is appreciated.
You can do both that you ask for.
To build a string directly, just append to it what you capture in the regex
my $string;
while (<$input_fh>)
{
my ($val) = /Current\s*value\s*=\s*(.*)/;
$string .= $val;
}
If the match fails then $val is an empty string, so we don't have to test. You can also write the whole while loop in one line
$string .= (/Current\s*value\s*=\s*(.*)/)[0] while <$input_fh>;
but I don't see why that would be necessary. Note that this reads from the filehandle, and line by line. There is no reason to first read all lines into an array.
To avoid (explicit) looping, you can read all lines and pass them through map, naively as
my $string = join '',
map { (/Current\s*value\s*=\s*(.*)/) ? $1 : () } <$input_fh>;
Since map needs a list, the filehandle is in list context, returning the list of all lines in the file. Then each is processed by code in map's block, and its output list is then joined.
The trick map { ($test) ? $val : () } uses map to also do grep's job, to filter -- the empty list that is returned if $test fails is flattened into the output list, thus disappearing. The "test" here is the regex match, which in the scalar context returns true/false, while the capture sets $1.
But, like above, we can return the first element of the list that match returns, instead of testing whether the match was successful. And since we are in map we can in fact return the "whole" list
my $string = join '',
map { /Current\s*value\s*=\s*(.*)/ } <$input_fh>;
what may be clearer here.
Comments on the code in the question
the while (#input) is an infinite loop, since #input never gets depleted. You'd need foreach (#input) -- but better just read the filehandle, while (<$input_fh>)
your regex does match on a line with that string, but it doesn't attempt to match the pattern that you need (what follows =). Once you add that, it need be captured as well, by ()
you can assign to the i-th element (which should be $i) but then you'd have to increment $i as you go. Most of the time it is better to just push #array, $value
You can use capturing parentheses to grab the string you want:
use strict;
use warnings;
my #arr;
open ( my $input_fh, '<', 'vcs_output.log' ) or die $!;
while (<$input_fh>) {
if (/Current value = (.)/) {
push #arr, $1;
}
}
close ( $input_fh );
print "#arr\n";
__END__
x x 1 0 x 0 x 1
Use grep and perlre
http://perldoc.perl.org/functions/grep.html
http://perldoc.perl.org/perlre.html
If on a non-Unix environment then...
#!/usr/bin/perl -w
use strict;
open (my $fh, '<', "vcs_output.log");
chomp (my #lines = <$fh>);
# Filter for lines which contain string 'Current value'
#lines = grep{/Current value/} #lines;
# Substitute out what we don't want... leaving us with the 'xx10x0x1'
#lines = map { $_ =~ s/.*Current value = //;$_} #lines;
my $str = join('', #lines);
print $str;
Otherwise...
#!/usr/bin/perl -w
use strict;
my $output = `grep "Current value" vcs_output.log | sed 's/.*Current value = //'`;
$output =~ s/\n//g;
print $output;
I am attempting to write a code that will encrypt letters with a basic cyclic shift cipher while leaving any character that is not a letter alone. I am trying to do this through the use of a sub that finds the new value for each of the letters. When I run the code now,it formats the result so there is a single space between every encrypted letter instead of keeping the original formatting. I also cannot get the result to be only in lowercase letters.
sub encrypter {
my $letter = shift #_;
if ($letter =~ m/^[a-zA-Z]/) {
$letter =~ y/N-ZA-Mn-za-m/A-Za-z/;
return $letter;
}
else {
return lc($letter);
}
}
print "Input string to be encrypted: ";
my $input = <STDIN>;
chomp $input;
print "$input # USER INPUT\n";
my #inputArray = split (//, $input);
my $i = 0;
my #encryptedArray;
for ($i = 0; $i <= $#inputArray; $i++) {
$encryptedArray[$i] = encrypter($inputArray[$i]);
}
print "#encryptedArray # OUTPUT\n";
The problem is how you are printing the array.
Change this line:
print "#encryptedArray # OUTPUT\n";
to:
print join("", #encryptedArray) . " # OUTPUT\n";
Here is an example that illustrates the problem.
#!/usr/bin/perl
my #array = ("a","b","c","d");
print "#array # OUTPUT\n";
print join("", #array) . " # OUTPUT\n";
Output:
$ perl test.pl
a b c d # OUTPUT
abcd # OUTPUT
According to the Perl documentation on print:
The current value of $, (if any) is printed between each LIST item.
The current value of $\ (if any) is printed after the entire LIST has
been printed.
So two others ways to do it would be:
#!/usr/bin/perl
my #array = ("a","b","c","d");
$,="";
print #array, " #OUTPUT\n";
or
#!/usr/bin/perl
my #array = ("a","b","c","d");
$"="";
print #array, " #OUTPUT\n";
Here is a related answer and here is documentation explaining $" and $,.
Those spaces in your output from $" (list separator) because you use print "#encryptedArray" to print that array, which equals print join($", #encryptedArray), therefore you could disable them by
local $" = '';
or you could join that #encryptedArray by yourself before you print it, just as suggested by #Matt.
Note that there is no need for such complexity. tr/// - also known as y/// - wil convert the whole string for you. Like this
use strict;
use warnings;
print "Input string to be encrypted: ";
chomp(my $input = <STDIN>);
print "$input # USER INPUT\n";
(my $encrypted = $input) =~ tr/N-ZA-Mn-za-m/A-Za-z/;
print "$encrypted # OUTPUT\n";
I'm working on a Perl project where i have a lot of strings containing ids and corresponding values in quotation marks, seperated by semicolons.
Example: main_id "1234567"; second_id "My_ID"; name "Andreas";
There is a blank behind every ID-name and behind every semicolon.
There are 2 problems I'm dealing with:
Problem 1: What is the fastest way to get the value (without quotation marks) to a specific id? My first try didn't work:
$id_list = 'main_id "1234567"; second_id "My_ID"; name "Andreas";';
$wanted_id = 'second_id';
($value = $id_list) =~ s/.*$wanted_id\w"([^"])";.*/$1/;
Problem 2: What is the fastest way to turn this string id into a hash for a specific id, that looks like this:
String: main_id "1234567"; second_id "My_ID"; name "Andreas";
Hash for "second_id":
hash{My_ID} = {main_id => 1234567, second_id => My_ID, name => Andreas}
What I tried:
$id_list = 'main_id "1234567"; second_id "My_ID"; name "Andreas";';
$wanted_id = 'second_id';
%final_id_hash;
%hash;
my #ids = split ";", $id_list;
foreach my $id (#ids) {
my ($a,$b)= split " ", $id;
$b =~ s/"//g;
$hash{$a} = $b;
}
$final_hash{$hash{$wanted_id}}= \%hash;
This worked, but is there a faster/better solution?
The Text::ParseWords module (part of the standard Perl distribution) makes this simple.e.
#!/usr/bin/perl
use strict;
use warnings;
use 5.010;
use Text::ParseWords;
use Data::Dumper;
my %final_hash;
my $wanted_id = 'second_id';
my $id_list = 'main_id "1234567"; second_id "My_ID"; name "Andreas";';
my #words = parse_line '[\s;]+', 0, $id_list;
pop #words; # Lose the extra field generated by the ; at the end
my %hash = #words;
$final_hash{$hash{$wanted_id}} = \%hash;
say Dumper \%final_hash;
Problem 1,
my %hash = map {
map { s/ ^" | "$ //xg; $_ } split /\s+/, $_, 2;
}
split /;\s+/, qq{main_id "1234567"; second_id "My_ID"; name "Andreas"};
use Data::Dumper; print Dumper \%hash;
I'm writing a Perl programm and I've got the following problem:
I have a large list of start and end positions in a string. This positions correspond to substrings in this string. I now want to transfer this positions to a second string. This second string is identical to the first string, except that it has additional hyphen.
Example for original String: "ABCDEF" and one Substring "BCDE"
What I have:
Positions of substring in this original string: Start = 1, End =
4
The original string with additional hyphen: "-AB---CD--E-F---"
What I want:
Position of the substring in the hyphen-string: Start=2, End=10
I have a large list of this substring positions.
I strongly suspect that you have shown a reduced version of the problem, in which case any solution may not work for the real situation.
However, it seems simplest to build a regex by interspersing -* (i.e. zero or more hyphens) between characters.
This program works that way, building a regex of B-*C-*D-*E and comparing it to both of your sample strings.
use strict;
use warnings;
my #strings = qw/ ABCDEF -AB---CD--E-F--- /;
my ($start, $end) = (1, 4);
my $substr = substr $strings[0], $start, $end-$start + 1;
my $regex = join '-*', split //, $substr;
$regex = qr/$regex/;
for my $string (#strings) {
if ($string =~ $regex) {
printf "Substring found at %d to %d in string %s\n", $-[0], $+[0]-1, $string;
}
}
output
Substring found at 1 to 4 in string ABCDEF
Substring found at 2 to 10 in string -AB---CD--E-F---
Does this work for you? It just searches for the characters specified by start and end in the hyphenated string and returns their indices.
sub hyphen_substrings {
my $original = shift;
my $hyphenated = shift;
my #substrings = #_;
my #return;
for my $substring (#substrings) {
my ($start, $end) = #{$substring}[0, 1];
my $start_h = index $hyphenated, substr $original, $start, 1;
my $end_h = index $hyphenated, substr $original, $end, 1;
push #return, [$start_h, $end_h];
}
return #return;
}
use strict;
use warnings;
my $theStringGivenAsAnInputExample="-AB---CD--E-F---";
my $start=1;
my $end=4;
my $theStringGivenAsAnotherInput="ABCDEF";
my $regexp=join("-*",split("",substr($theStringGivenAsAnotherInput,$start,$end))
);
$theStringGivenAsAnInputExample =~ /$regexp/p;
print ${^PREMATCH},"\n";
print ${^POSTMATCH},"\n";
print ${^MATCH},"\n";
my $startPosition = length(${^PREMATCH});
my $finishPosition = length(${^PREMATCH})+length(${^MATCH})-1;
print "start, $startPosition finish, $finishPosition\n";
I have a variable that is entered at a prompt:
my $name = <>;
I want to append a fixed string '_one'to this (in a separate variable).
E.g. if $name = Smith then it becomes 'Smith_one'
I have tried several various ways which do not give me the right results, such as:
my $one = "${name}_one";
^ The _one appears on the next line when I print it out and when I use it, the _one is not included at all.
Also:
my $one = $name."_one";
^ The '_one' appears at the beginning of the string.
And:
my $end = '_one';
my $one = $name.$end;
or
my $one = "$name$end";
None of these produce the result I want, so I must be missing something related to how the input is formatted from the prompt, perhaps. Ideas appreciated!
Your problem is unrelated to string appending: When you read a line (e.g. via <>), then the record input separator is included in that string; this is usually a newline \n. To remove the newline, chomp the variable:
my $name = <STDIN>; # better use explicit filehandle unless you know what you are doing
# now $name eq "Smith\n"
chomp $name;
# now $name eq "Smith"
To interpolate a variable into a string, you usually don't need the ${name} syntax you used. These lines will all append _one to your string and create a new string:
"${name}_one" # what you used
"$name\_one" # _ must be escaped, else the variable $name_one would be interpolated
$name . "_one"
sprintf "%s_one", $name
# etc.
And this will append _one to your string and still store it in $name:
$name .= "_one"