My code so far only reads lines 1 to 4 and prints them. What I want to do instead of printing them is putting them into an array. So any help would be greatly appreciated. And hopefully just the code since it should be short. I learn much faster looking at full code instead of opening another 50 tabs trying to put multiple concepts together. Hopefully I'll learn this at some point and won't require help.
my $x = 1;
my $y = 4;
open FILE, "file.txt" or die "can not open file";
while (<FILE>) {
print if $. == $x .. $. == $y;
}
You should just put each line in an array with push :
my $x = 1;
my $y = 4;
my #array;
open FILE, "file.txt" or die "can not open file";
while (<FILE>) {
push (#array, $_) if ($. >= $x || $. <= $y);
}
foreach at the end is just proof it works - note it doesn't ignore blank lines - figured you may want to keep them.
#!/usr/bin/perl
use warnings;
use strict;
my $fi;
my $line;
my $i = 0;
my #array;
open($fi, "< file.txt");
while ($line = <$fi>) {
$array[$i] = $line;
if ($i == 3)
{
last;
}
$i++;
}
foreach(#array)
{
print $_;
}
you know, you don't need to keep iterating through the file once you've got all the data you need.
my $x = 1;
my $y = 4;
my #array;
my $file = 'file.txt';
# Lexical filehandle, three-argument open, meaningful error message
open my $file_h, '<', $file or die "cannot open $file: $!";
while (<$file_h>) {
push #array $_ if $_ >= $x; # This condition is unnecessary when $x is 1
last if $. == $y;
}
Related
What this program is meant to do is that it reads a text file which looks like:
Item \t\t Price
apple \t\t 20
orange \t\t 50
lime \t\t 30
I'm using split function to split these 2 columns and then i should apply a -25% discount on all items and print it out to a new file. My code so far does what i want but the new text file has a '0' value under my last number in price column. I also get 2 errors if i run it with "use warnings" which are:
Use of uninitialized value $item in multiplication * ...
Use of uninitialized value $item[0] in concatenation (.) ...
I should also tell total number of items calculated but i get like 5 1's instead of 5. (11111 instead of 5)
use strict;
use warnings;
my $filename = 'shop.txt';
if (-e $filename){
open (IN, $filename);
}
else{
die "Can't open input file for reading: $!";
}
open (OUT,">","discount.txt") or die "Can't open output file for writing: $!";
my $header = <IN>;
print OUT $header;
while (<IN>) {
chomp;
my #items = split(/\t\t/);
foreach my $item ($items[1]){
my $discount = $item * (0.75);
print OUT "$items[0]\t\t$discount\n";
}
}
This is too complicated and not clear what are you doing in foreach loop and you are not skipping empty lines. Keep it simple:
use warnings;
use strict;
use v5.10;
<>; # skip header
while(my $line = <>)
{
chomp $line;
next unless ($line);
my ($title, $price ) = split /\s+/, $line;
if( $title && defined $price )
{
$price *= 0.75;
say "$title\t\t$price";
}
}
and run like
perl script.pl <input.txt >output.txt
use strict;
use warnings;
my $filename = 'shop.txt';
if (-e $filename){
open (IN, $filename);
}
else{
die "Can't open input file for reading: $!";
}
open (OUT,">","discount.txt") or die "Can't open output file for writing: $!";
my $header = <IN>;
my $item;
my $price;
print OUT $header;
while (<IN>) {
chomp;
($item, $price) = split(/\t\t/);
my $discount = $price*0.75;
print OUT "$item $discount\n";
}
This should help! :)
If the total item count isn't very important to you:
$ perl -wane '$F[1] *= 0.75 if $. > 1; print join("\t", #F), "\n";' input.txt
Output:
Item Price
apple 15
orange 37.5
lime 22.5
If you really need the total item count:
$ perl -we 'while (<>) { #F = split; if ($. > 1) { $F[1] *= 0.75; $i++ } print join("\t", #F), "\n"; } print "$i items\n";' input.txt
Output:
Item Price
apple 15
orange 37.5
lime 22.5
3 items
I'd use this approach
#!/usr/bin/perl
use strict;
use warnings;
my %items;
my $filename = 'shop.txt';
my $discount = 'discount.txt';
open my $in, '<', $filename or die "Failed to open file! : $!\n";
open my $out, ">", $discount or die "Can't open output file for writing: $!";
print $out "Item\t\tPrice\n";
my $cnt = 0;
while (my $line = <$in>) {
chomp $line;
if (my ($item,$price) = $line =~ /(\w.+)\s+([0-9.]+)/){
$price = $price * (0.75);
print $out "$item\t\t$price\n";
$items{$item} = $price;
$cnt++;
}
}
close($in);
close($out);
my $total = keys %items;
print "Total items - $total \n";
print "Total items - $cnt\n";
Using regex capture groups to capture the item and price (using \w.+ in case the item is 2 words like apple sauce), this will also prevent empty lines from printing to file.
I also hard coded the Item and Price header, probably a good idea if you are going to be using a consistent header.
Hope it helps
---Update ----
I added 2 examples of a total count in my script. The first one is using a hash and printing out the hash size, the second method is using a counter. The hash option is good except if your list has 2 items that are the same in which case the key of the hash will be overridden with the last item found which shares the same name. The counter is a simple solution.
I have a file with almost 1,500 names of Marvel heroes, each name in new line. I have to ask user what his favourite hero is and find out if it's a hero from the list or not. Here's what I have right now. It doesn't work: I can guess only the last hero from the list. For the rest it just prints that they are not on the list.
print "Whats your favourite hero?\n";
my $hero = <stdin>;
chomp $hero;
open FILE, "<list_marvel.txt";
my #marvel = <FILE>;
chomp(#marvel);
my $result = 0;
foreach (#marvel) {
if ($_ eq $hero);
}
if ($result == 1) {
print "That hero is on the list";
}
else {
print "$hero is not on the list.\n";
}
Here are two files:
-Perl code : Perl Code
-List of heroes : List
Your program has a syntax error and won't compile. It certainly won't find only the last name on the list
The main problem is that you never set $result, and if($_ eq $hero) should be something like $result = 1 if($_ eq $hero)
You must always use strict and use warnings at the top of every Perl program you write. It is an enormous help in finding straighforward problems
Here's a working version
use strict;
use warnings;
my $filename = 'list_marvel.txt';
open my $fh, '<', $filename or die qq{Unable to open "'list_marvel.txt'": $!};
print "Whats your favourite hero? ";
my $hero = <>;
chomp $hero;
my $found;
while ( <$fh> ) {
chomp;
if ( $_ eq $hero ) {
++$found;
last;
}
}
print $found ? "$hero is on the list\n" : "$hero is not on the list";
You don't set $result anywhere to true.
Make your foreach loop like this:
foreach(#marvel){
$result = $_ eq $hero;
}
or
foreach (#marvel){
$result = 1 if $_ eq $hero
}
You forgot to increment your $result. If you indent your code properly, it is easier to see.
foreach (#marvel) {
# here something is missing
if ( $_ eq $hero );
}
Add $result++ if $_ eq $hero; in the foreach.
You should always use strict and use warnings. That would have told you about a syntax error near );.
Also consider using the three argument open with lexical filehandles.
Rewritten it looks like this:
use strict;
use warnings;
use feature 'say'; # gives you say, which is print with a newline at the end
say "What's you favourite hero?";
my $hero = <STDIN>;
chomp $hero;
# alsways name variables so it's clear what they are for
my $found = 0;
# die with the reason of error if something goes wrong
open my $fh, '<', 'list_marvel.txt' or die $!;
# read the file line by line
while ( my $line = <$fh> ) {
chomp $line;
if ( $line eq $hero ) {
# increment so we know we 'found' the hero in the list
$found++;
# stop reading at the first hit
last;
}
}
close $fh;
# no need to check for 1, truth is enough
if ( $result ) {
say "That hero is on the list.";
}
else {
say "$hero is not on the list.";
}
First, you miss setting the $result at around if($_ eq $hero).
Then, you may wish to make you comparison case insensitive. This would require a regular expression, e.g.:
$result = 1 if (/^$hero$/i);
Just modified your code. After if condition increment $result. Always use use strict and use warnings and always use 3 arguments to open a file.
use strict;
use warnings;
print "Whats your favourite hero?\n";
my $hero = <stdin>;
chomp $hero;
open FILE, "<", "list_marvel.txt" or die $!;
chomp (my #marvel = <FILE>);
close FILE;
my $result = 0;
foreach my $name (#marvel)
{
if($name eq $hero)
{
$result++;
}
}
if ($result == 1)
{
print "That hero is in the list.\n";
}
else
{
print "$hero is not in the list.\n";
}
This will take a single user entry from STDIN. It will run through the file of hero names, and if one matches the user entry it will print the name and exit the loop. If the name is not found it will tell you:
use warnings;
use strict;
open my $file1, '<', 'input.txt' or die $!;
print "Enter hero: ";
chomp(my $hero = <STDIN>);
my $result = 0;
while(<$file1>){
chomp;
if (/$hero/){
print "$_\n";
$result++;
last;
}
}
print "hero not in list\n" if $result == 0;
I'm trying to count the number of 'N's in a FASTA file which is:
>Header
AGGTTGGNNNTNNGNNTNGN
>Header2
AGNNNNNNNGNNGNNGNNGN
so in the end I want to get the count of number of 'N's and each header is a read so I want to make a histogram so I would at the end output something like this:
# of N's # of Reads
0 300
1 240
etc...
so there are 300 sequences or reads that have 0 number of 'N's
use strict;
use warnings;
my $file = shift;
my $output_file = shift;
my $line;
my $sequence;
my $length;
my $char_N_count = 0;
my #array;
my $count = 0;
if (!defined ($output_file)) {
die "USAGE: Input FASTA file\n";
}
open (IFH, "$file") or die "Cannot open input file$!\n";
open (OFH, ">$output_file") or die "Cannot open output file $!\n";
while($line = <IFH>) {
chomp $line;
next if $line =~ /^>/;
$sequence = $line;
#array = split ('', $sequence);
foreach my $element (#array) {
if ($element eq 'N') {
$char_N_count++;
}
}
print "$char_N_count\n";
}
Try this. I changed a few things like using scalar file handles. There are many ways to do this in Perl, so some people will have other ideas. In this case I used an array which may have gaps in it - another option is to store results in a hash and key by the count.
Edit: Just realised I'm not using $output_file, because I have no idea what you want to do with it :) Just change the 'print' at the end to 'print $out_fh' if your intent is to write to it.
use strict;
use warnings;
my $file = shift;
my $output_file = shift;
if (!defined ($output_file)) {
die "USAGE: $0 <input_file> <output_file>\n";
}
open (my $in_fh, '<', $file) or die "Cannot open input file '$file': $!\n";
open (my $out_fh, '>', $output_file) or die "Cannot open output file '$output_file': $!\n";
my #results = ();
while (my $line = <$in_fh>) {
next if $line =~ /^>/;
my $num_n = ($line =~ tr/N//);
$results[$num_n]++;
}
print "# of N's\t# of Reads\n";
for (my $i = 0; $i < scalar(#results) ; $i++) {
unless (defined($results[$i])) {
$results[$i] = 0;
# another option is to 'next' if you don't want to show the zero totals
}
print "$i\t\t$results[$i]\n";
}
close($in_fh);
close($out_fh);
exit;
I am taking a total number of line as a user input and then I am deleting those numbers of l ine from the file.
I saw this learn.perl.org/faq/perlfaq5.html#How-do-I-count-the-number-of-lines-in-a-file- and then I tired the below simple logic.
Logic:
Get the Total number of lines
Subtracts it by the numbers entered by user
print the lines
Here is my code :
#!/usr/bin/perl -w
use strict;
open IN, "<", "Delete_line.txt"
or die " Can not open the file $!";
open OUT, ">", "Update_delete_line.txt"
or die "Can not write in the file $!";
my ($total_line, $line, $number, $printed_line);
print"Enter the number of line to be delete\n";
$number = <STDIN>;
while ($line = <IN>) {
$total_line = $.; # Total number of line in the file
}
$printed_line = $total_line - $number;
while ($line = <IN>) {
print OUT $line unless $.== $printed_line;
}
Well, neither i am getting any error in code nor any out put ? why I just don't know.
Can any one give me some suggestion.
A Perl solution that's efficient for large files requires the use of File::ReadBackwards
use File::ReadBackwards qw( );
my $num_lines = 10;
my $qfn = 'file.txt';
my $pos = do {
my $fh = File::ReadBackwards->new($qfn)
or die $!;
$fh->readline() for 1..$num_lines;
$fh->tell()
};
truncate($qfn, $pos)
or die $!;
This does not read the whole file twice (unlike the OP's method).
This does not read the whole file (unlike the Tie::File solutions).
This does not read the whole file into memory.
Yet another way is to use Tie::File
#!/usr/bin/env perl
use strict;
use warnings;
use Tie::File;
tie my #lines, 'Tie::File', 'myfile' or die "$!\n";
$#lines -= 10;
untie #lines;
This has the advantage of not loading the file into memory while acting like it does.
Here a solution that passes through a stream and prints all but the last n lines where n is a command line argument:
#!/usr/bin/perl
my #cache;
my $n = shift #ARGV;
while(<>) {
push #cache, $_;
print shift #cache if #cache > $n;
}
or the one-liner version:
perl -ne'BEGIN{$n=shift#ARGV}push#c,$_;print shift#c if#c>$n' NUMBER
After finishing reading from IN, you have to reopen it or seek IN, 0, 0 to reset its position. You also have to set $. to zero again.
Also, the final condition should be changed to unless $. > $printed_line so you skip all the lines over the threshold.
The "more fun" answer: use Tie::File!
use strict;
use warnings;
use Tie::File;
tie my #file, 'Tie::File', 'filename' or die "$!";
$#file -= 10;
Just read the file in reverse and delete the first n lines: -
open my $filehandle, "<", "info.txt";
my #file = <$filehandle>;
splice(#file, -10);
print #file;
Note: This loads the entire file into memory.
You could just buffer the last 10 lines and then not print out the remaining 10.
use English qw<$INPLACE_EDIT>;
{ local #ARGV = $name_of_file_to_edit;
local $INPLACE_EDIT = '.bak';
my #buffer;
for ( 1..$num_lines_to_trim ) {
push #buffer, <>;
}
while ( <> ) {
print shift #buffer;
push #buffer, $_;
}
}
You could also do this with File::Slurp::edit_file_lines:
my #buffer;
my $limit_reached = 0;
edit_file_lines {
push #buffer, $_;
return ( $limit_reached ||= #buffer > $num_lines_to_trim ) ? shift #buffer
: ''
;
} $name_of_file;
my $num_lines = 10;
my $qfn = 'file.txt';
system('head', '-n', -$num_lines, '--', $qfn);
die "Error" if $?;
Easy with a C like for :
#!/usr/bin/perl -w
use strict;
open(my $in,"<","Delete_line.txt") or die "Can not open the file $!";
open(my $out,">","Update_delete_line.txt") or die"Can not write in the file $!";
print"Enter the number of lines to be delete\n";
my $number=<STDIN>;
my #file = <$in>;
for (my $i = 0; $i < $#file - $number + 1; $i++) {
print $out $file[$i];
}
close $in;
close $out;
#
# Reads a file trims the top and the bottom of by passed num of lines
# and return the string
# stolen from : http://stackoverflow.com/a/9330343/65706
# usage :
# my $StrCatFile = $objFileHandler->ReadFileReturnTrimmedStrAtTopBottom (
# $FileToCat , $NumOfRowsToRemoveAtTop , $NumOfRowsToRemoveAtBottom) ;
sub ReadFileReturnTrimmedStrAtTopBottom {
my $self = shift ;
my $file = shift ;
my $NumOfLinesToRemoveAtTop = shift ;
my $NumOfLinesToRemoveAtBottom = shift ;
my #cache ;
my $StrTmp = () ;
my $StrReturn = () ;
my $fh = () ;
open($fh, "<", "$file") or cluck ( "can't open file : $file for reading: $!" ) ;
my $counter = 0;
while (<$fh>) {
if ($. >= $NumOfLinesToRemoveAtTop + 1) {
$StrTmp .= $_ ;
}
}
close $fh;
my $sh = () ;
open( $sh, "<", \$StrTmp) or cluck( "can't open string : $StrTmp for reading: $!" ) ;
while(<$sh>) {
push ( #cache, $_ ) ;
$StrReturn .= shift #cache if #cache > $NumOfLinesToRemoveAtBottom;
}
close $sh ;
return $StrReturn ;
}
#eof ReadFileReturnTrimmedStrAtTopBottom
#
I have a file which is tab delimited, and has two columns, A and B.
I want to count the number of times an element in B is repeated in A. I could have done it in Excel, but since the two columns contain more than 200k elements, it hangs.
I tried with this code but it counts elements in itself:
my %counts = ();
for (#A) {
$count{$_}++;
}
foreach my $k(keys %counts) {
print "$k\t$count{$k}\n";
}
Try this solution:
use strict;
use warnings;
my %countx;
my #y;
my $file = 'ab.txt';
open my $fh, '<', $file or die "Couldn't open $file";
while (my $line = <$fh>) {
chomp $line; # remove newline
# I've avoided using $a and $b because they are special variables in perl
my ( $x, $y ) = split /\t/, $line;
$countx{ $x }++;
push #y, $y;
}
close $fh;
foreach my $y (#y) {
my $count = $countx{ $y } || 0;
print "$y\t$count\n";
}