I have the following simple piece of code (identified as the problem piece of code and extracted from a much larger program).
Is it me or can you see an obvious error in this code that it stopping it from matching against $variable and printing $found when it definitely should be doing?
Nothing is printed when I try to print $variable, and there are definitely matching lines in the file I am using.
The code:
if (defined $var) {
open (MESSAGES, "<$messages") or die $!;
my $theText = $mech->content( format => 'text' );
print "$theText\n";
foreach my $variable (<MESSAGES>) {
chomp ($variable);
print "$variable\n";
if ($theText =~ m/$variable/) {
print "FOUND\n";
}
}
}
I have located this as the point at which the error is occurring but cannot understand why?
There may be something I am totally overlooking as its very late?
Update I have since realised that I misread your question and this probably doesn't solve the problem. However the points are valid so I am leaving them here.
You probably have regular expression metacharacters in $variable. The line
if ($theText =~ m/$variable/) { ... }
should be
if ($theText =~ m/\Q$variable/) { ... }
to escape any that there are.
But are you sure you don't just want eq?
In addition, you should read from the file using
while (my $variable = <MESSAGES>) { ... }
as a for loop will unnecessarily read the entire file into memory. And please use a better name than $variable.
This works for me.. Am I missing the question at hand? You're just trying to match "$theText" to anything on each line in the file right?
#!/usr/bin/perl
use warnings;
use strict;
my $fh;
my $filename = $ARGV[0] or die "$0 filename\n";
open $fh, "<", $filename;
my $match_text = "whatever";
my $matched = '';
# I would use a while loop, out of habit here
#while(my $line = <$fh>) {
foreach my $line (<$fh>) {
$matched =
$line =~ m/$match_text/ ? "Matched" : "Not matched";
print $matched . ": " . $line;
}
close $fh
./test.pl testfile
Not matched: this is some textfile
Matched: with a bunch of lines or whatever and
Not matched: whatnot....
Edit: Ah, I see.. Why don't you try printing before and after the "chomp()" and see what you get? That shouldn't be the issue, but it doesn't hurt to test each case..
Related
Not sure why this script isn't working. Can anyone suggest a fix in order to get the expected output?
Perl script:
open(INFILE,"test_input.txt")||die "can't open the file";
while(<INFILE>){
$_=~s/^\s+//;
$_=~s/\s+$//;
if ($_ =~ /work/){
<INFILE> or die "Bad file format";
my $model = INFILE;
print "line below search: $model\n";
if ($model =~/^good/){
print "found good word\n";
}
else{
print "no good word\n";
}
}
}
input file:
employment
work hard
good people
Expected Output:
line below search: good people
found good word
Actual Output:
line below search:
no good word
You were very close. To get your program running as you expected, I only had to make a couple of changes.
You have this code:
<INFILE> or die "Bad file format";
my $model = INFILE;
I think you're trying to ensure that there is actually another line after the one you've matched. But in the first of those lines, you just read the next line and throw the data away. And in the second of those lines, you set $model to the string "INLINE". Perhaps you meant my $model = <INFILE> - but even that doesn't give you what you want as you've already read (and discarded) the record you want in the previous line of code.
So I think you want to replace those two lines with a single line.
my $model = <INFILE> or die "Bad file format";
If you're interested, here's how I'd write this. Notice, I've got rid of the hard-coded file name. Instead, I read from the generic filehandle, <>. This is automatically connected to the file whose name is passed to the program on the command line. This has the advantage that the code is a) easier to write (as you don't need to explicitly open a file) and b) more flexible (as you can process a file with any name). I've also removed a few unnecessary uses of $_ =~.
#!/usr/bin/perl
# Always use these
use strict;
use warnings;
use feature 'say'; # for 'say()'
while (<>) {
s/^\s+//; # No need for $_ =~
s/\s+$//;
if (/work/) {
my $model = <> or die "Bad file format";
if ($model =~ /^good/) {
say 'found good word';
} else {
say 'no good word';
}
}
}
Try this.
Read file into array. Process line by line. You can the check the current and next line.
my $file = 'testFile.txt';
open my $fh, "<", "test_input.txt" or die "can't open the file";
chomp(my #data = <$fh>);
close $fh;
for my $index (0..$#data) {
if($data[$index] =~ /work/){
my $nextIndex = $index + 1;
die "Bad file format" unless(defined $data[$nextIndex]);
print "line below search: $data[$nextIndex]\n";
if ($data[$nextIndex] =~/^good/){
print "found good word\n";
}
else{
print "no good word\n";
}
}
}
I'm trying to replace a particular line in a file. I can get my program to run, but it doesn't actually do the replacing that I want it to.
Here is my sample file:
test line 1
test line 2
line to be overwritten
test line 3
Here is the code that I have:
my $origFile = $file_path . "junk\.file";
my $newFile = $file_path . "junk\.file\.backup";
# system command to make a backup of the file
system "mv $origFile $newFile";
#opens the files
open( my $INFILE, $newFile ) || die "Unable to read $newFile\n";
open( my $OUTFILE, '>' . $origFile ) || die "Unable to create $origFile\n";
# While loop to read in the file line by line
while ( <$INFILE> ) {
given ($_) {
when ("line to be overwritten") {
print $OUTFILE "line has been overwritten\n";
}
default {
print $OUTFILE $_;
}
}
}
close($INFILE);
close($OUTFILE);
I've tried to change the when statements several different ways to no avail:
when ($_ eq "line to be overwritten")
when ($_ == "line to be overwritten")
when ($_ cmp "line to be overwritten")
But those only generate errors. Anyone know what I'm doing wrong here?
As highlighted in a comment on the original question, given/when is an experimental feature of perl. I would personally recommend using if/else in a loop, and then either use string equality or a regex to match the line(s) you want to replace. A quick example:
use strict;
use warnings;
while(my $line = <DATA>) {
if ( $line =~ /line to be overwritten/ ) {
print "Overwritten\n";
} else {
print $line;
}
}
__DATA__
test line 1
test line 2
line to be overwritten
test line 3
This will give the output:
test line 1
test line 2
Overwritten
test line 3
You could also use the string equality if you aren't confident in your regex, or the string is guaranteed to be the same:
...
if ($line eq 'line to be overwritten') {
...
Sidenotes
open
On your initial open, it is recommended to use the 3 argument version of open to save from unexpected issues:
open(my $INFILE, '<', $newFile) || die "Unable to read $newFile\n";
(for more info on this, see here: http://modernperlbooks.com/mt/2010/04/three-arg-open-migrating-to-modern-perl.html)
strict & warnings
Also, it is recommended to use strict and warnings in your code file, as seen in my example above - this will save you from accidental mistakes like trying to use a variable which has not been declared, and syntax errors which may give you head-scratching results!
Experimental Features
Experimental features in perl are where there is no guarantee made for backwards compatibility to be maintained when a new release of perl comes out. Obviously if you are using the same version of perl everywhere it should be compatible, but things may break if you update to another major version of perl. answered here as I dont have the reputation to answer in the comments...
You seem to be making it way more complicated than it needs to be - a simple regex to check each line and act accordingly should do the job.
while(<$INFILE>)
{
chomp($_);
if /^line to be overwritten$/ )
{
print $OUTFILE "line has been overwritten\n";
}
else
{
print $OUTFILE "$_\n";
}
}
One way to do it is to use Tie::File module. It allows to replace data right in the file. You can make the backup same way you are currently doing, before changing the original file.
use strict;
use warnings;
use Tie::File;
my $file = 'test.txt';
tie my #textFile, 'Tie::File', $file, recsep => "\n" or die $!;
s/line to be overwritten/line has been overwritten/ for #textFile;
untie #textFile;
I am facing issues with perl chomp function.
I have a test.csv as below:
col1,col2
vm1,fd1
vm2,fd2
vm3,fd3
vm4,fd4
I want to print the 2nd field of this csv. This is my code:
#!/usr/bin/perl -w
use strict;
my $file = "test.csv";
open (my $FH, '<', $file);
my #array = (<$FH>);
close $FH;
foreach (#array)
{
my #row = split (/,/,$_);
my $var = chomp ($row[1]); ### <<< this is the problem
print $var;
}
The output of aboe code is :
11111
I really don't know where the "1" is comming from. Actually, the last filed can be printed as below:
foreach (#array)
{
my #row = split (/,/,$_);
print $row[1]; ### << Note that I am not printing "\n"
}
the output is:
vm_cluster
fd1
fd2
fd3
fd4
Now, i am using these field values as an input to the DB and the DB INSERT statement is failing due this invisible newline. So I thought chomp would help me here. instead of chomping, it gives me "11111".
Could you help me understand what am i doing wrong here.
Thanks.
Adding more information after reading loldop's responce:
If I write as below, then it will not print anything (not even the "11111" output mentioned above)
foreach (#array)
{
my #row = split (/,/,$_);
chomp ($row[1]);
my $var = $row[1];
print $var;
}
Meaning, chomp is removing the last string and the trailing new line.
The reason you see only a string of 1s is that you are printing the value of $val which is the value returned from chomp. chomp doesn't return the trimmed string, it modifies its parameter in-place and returns the number of characters removed from the end. Since it always removes exactly one "\n" character you get a 1 output for each element of the array.
You really should use warnings instead of the -w command-line option, and there is no reason here to read the entire file into an array. But well done on using a lexical filehandle with the three-parameter form of open.
Here is a quick refactoring of your program that will do what you want.
#!/usr/bin/perl
use strict;
use warnings;
my $file = 'test.csv';
open my $FH, '<', $file or die qq(Unable to open "$file": $!);
while (<$FH>) {
chomp;
my #row = split /,/;
print $row[1], "\n";
}
although, it is my fault at the beginning.
chomp function return 1 <- result of usage this function.
also, you can find this bad example below. but it will works, if you use numbers.
sometimes i use this cheat (don't do that! it is my bad-hack code!)
map{/filter/ && $_;}#all_to_filter;
instead of this, use
grep{/filter/}#all_to_filter;
foreach (#array)
{
my #row = split (/,/,$_);
my $var = chomp ($row[1]) * $row[1]; ### this is bad code!
print $var;
}
foreach (#array)
{
my #row = split (/,/,$_);
chomp ($row[1]);
my $var = $row[1];
print $var;
}
If you simply want to get rid of new lines you can use a regex:
my $var = $row[1];
$var=~s/\n//g;
So, I was quite frustrated with this easy looking task bugging me for the whole day long. I really appreciate everyone who responded.
Finaly I ended up using Text::CSV perl module and then calling each of the CSV field as array reference. There was no need left to run the chomp after using Text::CSV.
Here is the code:
#!/usr/bin/perl
use warnings;
use strict;
use Text::CSV;
my $csv = Text::CSV->new ( { binary => 1 } ) # should set binary attribute.
or die "Cannot use CSV: ".Text::CSV->error_diag ();
open my $fh, "<:encoding(utf8)", "vm.csv" or die "vm.csv: $!";
<$fh>; ## this is to remove the column headers.
while ( my $row = $csv->getline ($fh) )
{
print $row->[1];
}
and here is hte output:
fd1fd2fd3fd4
Later i was pulled these individual values and inserted into the DB.
Thanks everyone.
Perl is continuing to surprise me. I have a code which takes an input from the command line and checks if it is in a file. I have a file like this:
ls
date
pwd
touch
rm
First i read this file as
open(MYDATA,"filename") or die "Can not open file\n";
#commandlist = <MYDATA>;
chomp #commandlist;
close MYDATA;
the argument is in $commandname variable. To check if it is correct i printed to screen.
print $commandname."\n";
it works well. then i write the code.
$count = #commandlist;
for($i=0;$i < $count;$i++)
{
print $commandname;
print $commandlist[$i];
print "\n";
if($commandname eq $commandlist[$i])
{
print "equal\n";
}
}
and it does not print 'equal'. but it should do becaues $commandname variable has the value 'ls' which is in the file. i also print the value of $commandname and $commandlist[$i] to see if "visibly" they are equal and i get the output:
ls
lsls
lsdate
lspwd
lstouch
lsrm
here i see that they got the same value but why never eq operator evaluates to zero.
Additionally to get this task done, I have tried various methods all of which come to be useless like making a hash from the array and using exists.
I am struggling for this seemingly easy problem for a day but i just dont get it.
Thanks in advance
EDIT:
when i change the above loop as below
$count = #commandlist;
for($i=0;$i < $count;$i++)
{
print $commandlist[$i];
print $commandname;
print "\n";
if($commandname eq $commandlist[$i])
{
print "equal\n";
}
}
I got an output like.
ls
ls
lste
lsd
lsuch
ls
it seems like for some reason it overwrites some characters.
EDIT:
my whole script is like:
#reading file code, i posted above
while(<>)
chomp($_);
$commandname = $_;
if($commandname eq "start"){
##something here
} elsif ($commandname eq "machines"){
##something here
} else {
$count = #commandlist;
for($i=0;$i < $count;$i++)
{
print $commandlist[$i];
print $commandname;
print "\n";
if($commandname eq $commandlist[$i])
{
print "equal\n";
}
}
}
A bit change in the code would result in what you are looking for, "chomp" the string from array before you put it for comparison. Here it is
chomp $commandlist[$i];
if($commandname eq $commandlist[$i])
{
print "equal\n";
}
EDIT: as per perldoc chomp when you are chomping a list you should parenthesis. So, in your case ... instead simply saying
chomp #commandlist
make it like
chomp(#commandlist)
FINAL EDIT: I tried this and worked fine. Give it a try
$commandname = $ARGV[0];
open(MYDATA,"chk.txt") or die "Can not open file\n";
#commandlist = <MYDATA>;
chomp(#commandlist);
close MYDATA;
print $commandname."\n";
$count = #commandlist;
print $commandname;
for($i=0;$i < $count;$i++)
{
print $commandlist[$i];
print "\n";
if($commandname eq $commandlist[$i])
{
print "equal\n";
}
}
The overwritting indicates the presence of a CR. The lines end with CR LF, but you only remove the LF with chomp. Change
while (<>) {
chomp($_)
to
while (<>) {
s/\s+\z//;
You might consider restructuring your code as:
my $path='filename';
my $match='ls';
part 1 - read the file
open(my $fh, '<', $path) or die "failed to open $path: $!";
my #commandlist=<$fh>;
chomp #commandlist;
# or you can combine these lines as:
# chomp(my #commandlist=<$fh>);
# because chomp operates on the array itself rather than making a copy.
close($fh);
or
use File::Slurp qw/ read_file /;
# see http://search.cpan.org/dist/File-Slurp/lib/File/Slurp.pm
my #commandlist=read_file($path); # result is pre-chomped!
part 2 - check for a match
foreach my $command (#commandlist) {
print "$match equals $command\n" if $match eq $command;
}
One important consideration is that each line in your file must contain only the command name and cannot begin or end with any spaces or tabs. To compensate for possible leading or trailing whitespace, try:
foreach my $command (#commandlist) {
$command=~s/^\s+|\s+$//g; # strip leading or trailing whitespace
print "$match equals $command\n" if $match eq $command;
}
And finally, always start your Perl script with a Perl developer's bestest friends:
use strict;
use warnings;
which will catch most (if not all) errors caused by sloppy programming practice. (We all suffer from this!)
This is a beginner-best-practice question in perl. I'm new to this language. The question is:
If I want to process the output lines from a program, how can I format THE FIRST LINE in a special way?
I think of two possibilities:
1) A flag variable, once the loop is executed first time is set. But it will be evaluated for each cycle. BAD solution
2) An index-based loop (like a "for"). Then I would start the loop in i=1. This solution is far better. The problem is HOW CAN I DO IT?
I just found the code for looping over with the while ( <> ) construct.
Here you can see better:
$command_string = "par-format 70j p0 s0 < " . $ARGV[0] . "|\n";
open DATA, $command_string or die "Couldn't execute program: $!";
print "\t <div>          |-- <strong>Description</strong></div>\n";
while ( defined( my $line = <DATA> ) ) {
chomp($line);
# print "$line\n";
print "\t <div>          |   -- " . $line . "</div>\n";
}
close DATA;
Please also don't hesitate in correcting any code in here, this is my first perl poem.
Thanks!
You can always use $. or the English name $INPUT_LINE_NUMBER to control the logic in your loop with:
while (my $line = <>) {
if ($. == 1) {
# do cool stuff here
}
# do normal stuff here
}
To handle the first line differently, you could just put
$line = <DATA>;
above your loop.
With proper checking for read problems (empty file, etc.) this should be
if ($line = <DATA>) {
...do special things...
}
while (my $line = <DATA>) {
...do regular things...
}
I'm not sure about the defined() call. You might not need it, since an empty string has a false truth value.
From a 'best practices' perspective there is much wrong with that code sample:
open DATA, $command_string or die "Couldn't execute program: $!";
Security hole, please exploit me.
DATA is a magical value that points to a __DATA__ section at the end of the current file.
You should use
open my $fh
Which uses a lexical variable for a file handle instead of a global.
You should use 3 arg open, ie:
open my $fh, '<' , $filename
open my $fh, '-|' , $command
open my $fh, '-|' , $command, #args
sadly I have yet to work out how 3-arg works with dual-pipes.
theres' this IPC::Open2 thing, but I haven't worked out how
to use that effectively yet. Suggestions welcome .