I have a perl script generator.pl that defines some routines like:
sub a($) {
...
print FILE "$_[0]";
...
}
...
sub b($$) {
...
print FILE "$_[0], $_[1]";
...
}
...
$subsfile = $ARGV[0] . "/subs.pl";
$generatedfile = $ARGV[0] . "/generated.file";
open FILE, '>>', "$generatedfile" or die "error trying to append: $!";
do "$subsfile";
close FILE;
Let's assume that, for example subs.pl is like this:
a(1);
a(x);
b(1-2, z);
b(1-x, i);
b(y-z, j);
I call generator script in this way:
C:\Users\Me>perl generator.pl "D:/another/path"
Result is that D:/another/path/generated.file is created but it contains 0 bytes. Printing "print $#;" after do statement, I'm obtaining:
Transliteration pattern not terminated at...
If I try to call the script with a subs.pl having each actual argument double quoted
a("1");
a("x");
b("1-2", "z");
b("1-x", "i");
...
it works.
How can I do to make things work without using double quotes?
tr/// is transliteration operator which can be also written as y///. Further, it can be modified to take another character as delimiter, ie. y---.
So when perl see something like,
b(y-z, j);
it expects
b(y-z, j--);
which is correct and would in example above count all occurrences of z, ,, , and j chars in default variable $_, and pass it as argument to b().
Since compiler expectations are not met, it throws:
Transliteration pattern not terminated at...
Related
I have the following code snippet in Perl:
my $argsize = #args;
if ($argsize >1){
foreach my $a ($args[1..$argsize-1]) {
$a =~ s/(.*[-+*].*)/\($1\)/; # if there's a math operator, put in parens
}
}
On execution I'm getting "Use of unitialized value $. in range (or flip) , followed by Argument "" isn't numeric in array element at... both pointing to the foreach line.
Can someone help me decipher the error message (and fix the problem(s))? I have an array #args of strings. The code should loop through the second to n't elements (if any exist), and surround individual args with () if they contain a +,-, or *.
I don't think the error stems from the values in args, I think I'm screwing up the range somehow... but I'm failing when args has > 1 element. an example might be:
<"bla bla bla"> <x-1> <foo>
The long and short of it is - your foreach line is broken:
foreach my $a (#args[1..$argsize-1]) {
Works fine. It's because you're using a $ which says 'scalar value' rather than an # which says array (or list).
If you use diagnostics you get;
Use of uninitialized value $. in range (or flip) at
(W uninitialized) An undefined value was used as if it were already
defined. It was interpreted as a "" or a 0, but maybe it was a mistake.
To suppress this warning assign a defined value to your variables.
To help you figure out what was undefined, perl will try to tell you
the name of the variable (if any) that was undefined. In some cases
it cannot do this, so it also tells you what operation you used the
undefined value in. Note, however, that perl optimizes your program
and the operation displayed in the warning may not necessarily appear
literally in your program. For example, "that $foo" is usually
optimized into "that " . $foo, and the warning will refer to the
concatenation (.) operator, even though there is no . in
your program.
You can reproduce this error by:
my $x = 1..3;
Which is actually pretty much what you're doing here - you're trying to assign an array value into a scalar.
There's a load more detail in this question:
What is the Perl context with range operator?
But basically: It's treating it as a range operator, as if you were working your way through a file. You would be able to 'act on' particular lines in the file via this operator.
e.g.:
use Data::Dumper;
while (<DATA>) {
my $x = 2 .. 3;
print Dumper $x;
print if $x;
}
__DATA__
line one
another line
third line
fourth line
That range operator is testing line numbers - and because you have no line numbers (because you're not iterating a file) it errors. (But otherwise - it might work, but you'd get some really strange results ;))
But I'd suggest you're doing this quite a convoluted way, and making (potentially?) an error, in that you're starting your array at 1, not zero.
You could instead:
s/(.*[-+*].*)/\($1\)/ for #args;
Which'll have the same result.
(If you need to skip the first argument:
my ( $first_arg, #rest ) = #args;
s/(.*[-+*].*)/\($1\)/ for #rest;
But that error at runtime is the result of some of the data you're feeding in. What you've got here though:
use strict;
use warnings;
my #args = ( '<"bla bla bla">', '<x-1>', '<foo>' );
print "Before #args\n";
s/(.*[-+*].*)/\($1\)/ for #args;
print "After: #args\n";
I have a subroutine called grepText, which simply greps a text from another variable. I am trying to split the output. Is it possible to pass the output of grepText as an argument to split directly? without putting the value of grepText in a variable first ? grepText returns a string.
What i am trying to do is:
$output = (split ":", grepText("findThis", $Alltext))[1];
grepText is as follows
sub grepText(){
my #text = split "\n", $_[1];
my $output = grep /$_[0]/, #text;
return $output;
}
it doesn't work. Error is
Too many arguments for main::grepText at a line 115, near "$Alltext)"
It is very much possible to pass the input of a subroutine to any perl function directly without using a perl variable.
I think the issue might be with your "grepText" subroutine. To debug the issue in detail, much more information is required.
I did try your routine and I was able to get the required output:
#!/usr/bin/perl
sub grepText
{
return "hello:world"; # returns a test string
}
my $output = (split ":", grepText($textToFind, $Alltext))[1];
print "$output";
Output:
world
Sure it is. But as you've written it grepText is getting some strange parameters. In
(split ":", grepText(/$textToFind/, $Alltext))[1];
you're calling grepText(/$textToFind/, $Alltext) which is searching for the value of $textToFind in the global variable $_ and, in list context, is inserting either an empty list () or a list containing 1 (1) into the parameters
So you're calling grepText($Alltext) or grepText(1, $Alltext) depending on whether $_ contains the regex pattern in $textToFind
I'm pretty certain that's not what you want to do, so some more information would be nice!
However, whatever grepText returns will be split on colons : and (split ":", grepText(...))[1] will give you the second colon-separated field, which seems to be what you're asking
I'm a little noobish to perl coding conventions, could someone help explain:
why are there / and /< in front of perl variables?
what does\= and =~ mean, and what is the difference?
why does the code require an ending / before the ;, e.g. /start=\'([0-9]+)\'/?
The 1st 3 sub-questions were sort of solved by really the perldocs, but what does the following line means in the code?
push(#{$Start{$start}},$features);
i understand that we are pushing the $features into a #Start array but what does #$Start{$start} mean? Is it the same as:
#Start = ($start);
Within the code there is something like this:
use FileHandle;
sub open_infile {
my $file = shift;
my $in = FileHandle->new($file,"<:encoding(UTF-8)")
or die "ERROR: cannot open $file: $!\n" if ($Opt_utf8);
$in = new FileHandle("$file")
or die "ERROR: cannot open $file: $!\n" if (!$Opt_utf8);
return $in;
}
$uamf = shift #ARGV;
$uamin = open_infile($uamf);
while (<$uamin>) {
chomp;
if(/<segment /){
/start=\'([0-9]+)\'/;
/end=\'([0-9]+)\'/;
/features=\'([^\']+)\'/;
$features =~ s/annotation;//;
push(#{$Start{$start}},$features);
push(#{$End{$end}},$features);
}
}
EDITED
So after some intensive reading of the perl doc, here's somethings i've gotten
The /<segment / is a regex check that checks whether the readline
in while (<$uamin>) contains the following string: <segment.
Similarly the /start=\'([0-9]+)\'/ has nothing to to do with
instantiating any variable, it's a regex check to see whether the
readline in while (<$uamin>) contains start=\'([0-9]+)\' which
\'([0-9]+)\' refers to a numeric string.
In $features =~ s/annotation;// the =~ is use because the string
replacement was testing a regular expression match. See
What does =~ do in Perl?
Where did you see this syntax (or more to the point: have you edited stuff out of what you saw)? /foo/ represents the match operator using regular expressions, not variables. In other words, the first line is checking to see if the input string $_ contains the character sequence <segment.
The subsequent three lines essentially do nothing useful, in the sense that they run regular expression matches and then discard the results (there are side-effects, but subsequent regular expressions discard the side-effects, too).
The last line does a substitution, replacing the first occurance of the characters annotation; with the empty string in the string $features.
Run the command perldoc perlretut to learn about regex in Perl.
I have basically the following perl I'm working with:
open I,$coupon_file or die "Error: File $coupon_file will not Open: $! \n";
while (<I>) {
$lctr++;
chomp;
my #line = split/,/;
if (!#line) {
print E "Error: $coupon_file is empty!\n\n";
$processFile = 0; last;
}
}
I'm having trouble determining what the split/,/ function is returning if an empty file is given to it. The code block if (!#line) is never being executed. If I change that to be
if (#line)
than the code block is executed. I've read information on the perl split function over at
http://perldoc.perl.org/functions/split.html and the discussion here about testing for an empty array but not sure what is going on here.
I am new to Perl so am probably missing something straightforward here.
If the file is empty, the while loop body will not run at all.
Evaluating an array in scalar context returns the number of elements in the array.
split /,/ always returns a 1+ elements list if $_ is defined.
You might try some debugging:
...
chomp;
use Data::Dumper;
$Data::Dumper::Useqq = 1;
print Dumper( { "line is" => $_ } );
my #line = split/,/;
print Dumper( { "split into" => \#line } );
if (!#line) {
...
Below are a few tips to make your code more idiomatic:
The special variable $. already holds the current line number, so you can likely get rid of $lctr.
Are empty lines really errors, or can you ignore them?
Pull apart the list returned from split and give the pieces names.
Let Perl do the opening with the "diamond operator":
The null filehandle <> is special: it can be used to emulate the behavior of sed and awk. Input from <> comes either from standard input, or from each file listed on the command line. Here's how it works: the first time <> is evaluated, the #ARGV array is checked, and if it is empty, $ARGV[0] is set to "-", which when opened gives you standard input. The #ARGV array is then processed as a list of filenames. The loop
while (<>) {
... # code for each line
}
is equivalent to the following Perl-like pseudo code:
unshift(#ARGV, '-') unless #ARGV;
while ($ARGV = shift) {
open(ARGV, $ARGV);
while (<ARGV>) {
... # code for each line
}
}
except that it isn't so cumbersome to say, and will actually work.
Say your input is in a file named input and contains
Campbell's soup,0.50
Mac & Cheese,0.25
Then with
#! /usr/bin/perl
use warnings;
use strict;
die "Usage: $0 coupon-file\n" unless #ARGV == 1;
while (<>) {
chomp;
my($product,$discount) = split /,/;
next unless defined $product && defined $discount;
print "$product => $discount\n";
}
that we run as below on Unix:
$ ./coupons input
Campbell's soup => 0.50
Mac & Cheese => 0.25
Empty file or empty line? Regardless, try this test instead of !#line.
if (scalar(#line) == 0) {
...
}
The scalar method returns the array's length in perl.
Some clarification:
if (#line) {
}
Is the same as:
if (scalar(#line)) {
}
In a scalar context, arrays (#line) return the length of the array. So scalar(#line) forces #line to evaluate in a scalar context and returns the length of the array.
I'm not sure whether you're trying to detect if the line is empty (which your code is trying to) or whether the whole file is empty (which is what the error says).
If the line, please fix your error text and the logic should be like the other posters said (or you can put if ($line =~ /^\s*$/) as your if).
If the file, you simply need to test if (!$lctr) {} after the end of your loop - as noted in another answer, the loop will not be entered if there's no lines in the file.
In Perl, I need to read a .conf file that contains either a 0 or a 1. If the value is one, I need to execute whatever is in the if statement. Here is what I have now:
open(CONF, "/var/web/onhit.conf");
if(<CONF>) {
print "Hello World!";
}
close(CONF);
The contents of the if statement always evaluate, even if the .conf file contains a 0. I know the file reading is correct because this code can read the file correctly:
open(CONF, "/var/web/onhit.conf");
print <CONF>;
close(CONF);
If the file contains a 1, it prints a 1, and vice versa. Does anyone know what is wrong with my first snippet? Sorry, but I am a n00b at Perl. :-)
EDIT: Apparently, you had the truth value of your post inverted, and you meant to say that the if() statement always executed. This makes sense. What happens is that <CONF> reads in the string "1\n" or "0\n", not the number 1 or 0. The trailing newline prevents "0" from evaluating as false, so you need to chomp() it (or use the int() function, as mentioned in the other post). Either way should work.
(Note that, unfortunately, chomp() does not return the chomp()ed string, but a count of how many characters it removed, so you can't just say if(chomp(my $tmp = <CONF>)) and be done with it.)
Anyway, this is what I did:
open(CONF, "/var/web/onhit.conf");
chomp(my $tmp = <CONF>);
if($tmp) {
print "Hello, world!\n";
}
close CONF;
A few recommendations:
Consider using the three-argument form of open(), or at least specifying "<" in front of the filename.
Consider using a variable to hold a filehandle ($conf) rather than using the older, clumsier filehandle form (CONF).
This is the code I would have written:
open my $conf, "<", "/var/web/onhit.conf";
chomp(my $tmp = <$conf>);
if($tmp) {
print "Hello, world!\n";
}
close $conf;
You simply need to convert the string to an integer using the int function.
open(CONF, "/var/web/onhit.conf");
if(int(<CONF>)) {
print "Hello World!";
}
close(CONF);
Or you could just include in the newline in the comparison:
if (<CONF> =~ /^1$/) {
}