I have a subfunction and inside of it I am reading a file in Perl with the usual while-loop line-by-line because that's the only (and best?) option I know in Perl so far. Now I am searching line-based for a keyword with a loop like
my $var;
open(FILE, "stuff.dat")
while (my $line = <FILE>){
if ($line =~ /regex/) {
$var = $1;
return $var;
} else {
return "var is not defined!";
}
}
close(FILE);
but even when it gets the keyword and $var is specified, it gets overwritten on the next line. So I want to quit the while-loop if the keyword is found and $var is defined.
I tried next if or next unless or the last-exit but this isn't working properly and perldoc states that we can't use last for subs.
open(my $FILE, "<", "stuff.dat") or die $!;
while (my $line = <$FILE>){
if ($line =~ /regex/) {
return $1 if defined $1;
}
}
close($FILE);
return "var is not defined!";
open(FILE, "stuff.dat")
my $var;
while (my $line = <FILE>){
if ($line =~ /regex/) {
$var = $1;
last;
}
}
close(FILE);
return $var;
Hope this helps.
You can add the regexp evaluation to the while loop condition, without using return or last.
sub check_file {
open(FILE, "stuff.dat") or die;
my $result;
my $line;
while (($line = <FILE>) && ($result = ($line !~ m/regex/))) {};
close(FILE);
## $result equals 1 only if we have exit the loop and
## didn't have a match till the last line of the file
return ($result != 1);
}
Related
I have a text file where is lot of lines, I need search in this file keywords and if exist write to log file line where is keywords and line one line below and one above the keyword. Now search or write keyword not function if find write all and I dont known how can I write line below and above. Thanks for some advice.
my $vstup = "C:/Users/Omega/Documents/Kontroly/testkontroly/kontroly20220513_154743.txt";
my $log = "C:/Users/Omega/Documents/Kontroly/testkontroly/kontroly.log";
open( my $default_fh, "<", $vstup ) or die $!;
open( my $main_fh, ">", $log ) or die $!;
my $var = 0;
while ( <$default_fh> ) {
if (/\Volat\b/)
$var = 1;
}
if ( $var )
print $main_fh $_;
}
}
close $default_fh;
close $main_fh;
The approach below use one semaphore variable and a buffer variable to enable the desired behavior.
Notice that the pattern used was replaced by 'A` for simplicity testing.
#!/usr/bin/perl
use strict;
use warnings;
my ($in_fh, $out_fh);
my ($in, $out);
$in = 'input.txt';
$out = 'output.txt';
open($in_fh, "< ", $in) || die $!."\n";
open($out_fh, "> ", $out) || die $!;
my $p_next = 0;
my $p_line;
while (my $line = <$in_fh>) {
# print line after occurrence
print $out_fh $line if ($p_next);
if ($line =~ /A/) {
if (defined($p_line)) {
# print previous line
print $out_fh $p_line;
# once printed undefine variable to avoid printing it again in the next loop
undef($p_line);
}
# Print current line if not already printed as the line follows a pattern
print $out_fh $line if (!$p_next);
# toggle semaphore to print the next line
$p_next = 1;
} else {
# pattern not found.
# if pattern was not detected in both current and previous line.
$p_line = $line if (!$p_next);
$p_next = 0;
}
}
close($in_fh);
close($out_fh);
I have a file handle to read data from a file or from a pipe. Firstly, I read one line from the file handle. Then, I need to execute a while loop, taking into account the previously-read line. I think the seek function is problematic with pipes.
So my pseudocode is
local $line = <INPUT>;
seek(INPUT, -length($line), 1);
# if block
while (<INPUT>) {
}
Perhaps, there is a solution like this one?
while ($line, <INPUT>) {
}
Looking backward:
my $prev;
while (defined( my $line = <> )) {
... Use $prev and $line. $prev might not be defined. ...
$prev = $line;
}
Looking forward:
my $line = <>;
while (defined($line)) {
my $next = <>;
... Use $line and $next. $next might not be defined. ...
$line = $next;
}
In pairs:
if (defined( my $line1 = <> )) {
while (defined( my $line2 = <> )) {
... Use $line1 and $line2. Both will be defined. ...
$line1 = $line2;
}
}
Just remember the first line in a variable. Read the next line from the filehandle at the end of the loop:
#!/usr/bin/perl
use warnings;
use strict;
open my $FH, '-|', 'echo 3 ; seq 1 10' or die $!;
if (defined( my $first = <$FH> )) {
my $line = $first;
while () {
chomp $line;
print "$line:$first";
last if eof $FH;
$line = <$FH>;
}
}
A lot depends on why you want to do this. The easiest way is just to write a while read loop and save the line the first time it is executed. There's probably no need to read the first line and then also feed it into the read loop
Something like this perhaps
my $first_line;
while ( <> ) {
$first_line //= $_;
# Process $_
}
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 have written the following program with the hope of getting success. But I could never get it.
my $fileName = 'myfile.txt';
print $fileName,"\n";
if (open MYFILE, "<", $fileName) {
my $Data;
{
local $/ = undef;
$Data = <MYFILE>;
}
my #values = split('\n', $Data);
chomp(#values);
if($values[2] eq '9999999999') {
print "Success"."\n";
}
}
The content of myfile.txt is
160002
something
9999999999
700021
Try splitting by \s*[\r\n]+
my $fileName = 'myfile.txt';
print $fileName,"\n";
if (open MYFILE, "<", $fileName) {
my $Data;
{
local $/ = undef;
$Data = <MYFILE>;
}
my #values = split(/\s*[\r\n]+/, $Data);
if($values[2] eq '9999999999') {
print "Success";
}
}
If myfile.txt contain carriage return (CR, \r), it will not work as expected.
Another possible cause is trailing spaces before linefeed (LF, \n).
You don't need to read an entire file into an array to check one line. Open the file, skip the lines you don't care about, then play with the line you do care about. When you've done what you need to do, stop reading the file. This way, only one line is ever in memory:
my $fileName = 'myfile.txt';
open MYFILE, "<", $fileName or die "$filename: $!";
while( <MYFILE> ) {
next if $. < 3; # $. is the line number
last if $. > 3;
chomp;
print "Success\n" if $_ eq '9999999999';
}
close MYFILE;
my $fileName = 'myfile.txt';
open MYFILE, "<", $fileName || die "$fileName: $!";
while( $rec = <MYFILE> ) {
for ($rec) { chomp; s/\r//; s/^\s+//; s/\s+$//; } #Remove line-feed and space characters
$cnt++;
if ( $rec =~ /^9+$/ ) { print "Success\n"; last; } #if record matches "9"s only
#print "Success" and live the loop
}
close MYFILE;
#Or you can write: if ($cnt==3 and $rec =~ /^9{10}$/) { print "Success\n"; last; }
#If record 3 matches ten "9"s print "Success" and live the loop.
This gives the whole line:
#!/usr/bin/perl
$file = 'output.txt';
open(txt, $file);
while($line = <txt>) {
print "$line" if $line =~ /_NN/;
}
close(txt);
#!/usr/bin/perl
use strict;
use warnings FATAL => "all";
binmode(STDOUT, ":utf8") || die;
my $file = "output.txt";
open(TEXT, "< :utf8", $file) || die "Can't open $file: $!";
while(<TEXT>) {
print "$1\n" while /(\w+)_NN\b/g;
}
close(TEXT) || die "Can't close $file: $!";
Your answer script reads a bit awkwardly, and has a couple of potential errors. I'd rewrite the main logic loop like so:
foreach my $line (grep { /expend_VB/ } #sentences) {
my #nouns = grep { /_NN/ } split /\s+/, $line;
foreach my $word (#nouns) {
$word =~ s/_NN//;
print "$word\n";
}
print "$line\n" if scalar(#nouns);
}
You need to put the my declaration inside the loop - otherwise it will persist longer than you want it to, and could conceivably cause problems later.
foreach is a more common perl idiom for iterating over a list.
print "$1" if $line =~ /(\S+)_NN/;
#!/usr/bin/perl
use strict;
use warnings FATAL => "all";
my $search_key = "expend"; ## CHANGE "..." to <>
open(my $tag_corpus, '<', "ch13tagged.txt") or die $!;
my #sentences = <$tag_corpus>; # This breaks up each line into list
my #words;
for (my $i=0; $i <= #sentences; $i++) {
if ( defined( $sentences[$i] ) and $sentences[$i] =~ /($search_key)_VB.*/i) {
#words = split /\s/,$sentences[$i]; ## \s is a whitespace
for (my $j=0; $j <= #words; $j++) {
#FILTER if word is noun:
if ( defined( $words[$j] ) and $words[$j] =~ /_NN/) {
#PRINT word and sentence:
print "**",split(/_\S+/,$words[$j]),"**", "\n";
print split(/_\S+/,$sentences[$i]), "\n"
}
} ## put print sentences here to print each sentence after all the nouns inside
}
}
close $tag_corpus || die "Can't close $tag_corpus: $!";