I am trying to get that Perl split working for more than 2 hours. I don't see an error. Maybe some other eyes can look at it and see the issue. I am sure its a silly one:
#versionsplit=split('.',"15.0.3");
print $versionsplit[0];
print $versionsplit[1];
print $versionsplit[2];
I just get an empty array. Any idea why?
You need:
#versionsplit=split(/\./,"15.0.3");
The first argument to split is a regular expression, not a string. And . is the regex symbol which means ‘match any character’. So all the characters in your input string were being treated as separators, and split wasn't finding anything between them to return.
the "." represents any character.You need to escape it for split function to recognise as a field separator.
change your line to
#versionsplit=split('\.',"15.0.3");
Related
My problem is that the return value im printing is not being translated into a value.
I have the following code in a test file.
#!/usr/bin/perl -I/srv/www/jonathan/m/www
my $var = sprintf("$%.1f lbs",(77*2.20462));
print $var;
Its returning: 0.1f instead of the value i need to see.
What am i doing incorrectly here? I'm a perl newbie.
Your problem is that Perl interprets "$%.1f" as the variable $% followed by ".1f". $% is a special Perl variable containing "The current page number of the currently selected output channel" (see perlvar) and that has the value 0, so what gets printed is the string "0.1f".
There are a few ways round this.
You can remove the dollar sign: sprintf("%.1f lbs",(77*2.20462)). But that changes the string that you display.
You can escape the dollar to tell Perl that it's not special: sprintf("\$%.1f lbs",(77*2.20462)).
But I think there's a better solution. Perl treats dollar signs as special characters in double-quoted strings. But there's no reason for your string to be double-quoted. So just change your format string to use single quotes: sprintf('$%.1f lbs',(77*2.20462)).
That last one is the solution I'd use.
Perl uses dolar($) symbol to declare a scalar variable, you need to remove the $ symbol from the sprintf.
corrected code
my $var = sprintf("%.1f lbs",(77*2.20462));
print $var;
output
169.8 lbs
I was trying to play with the . and , operators in Perl and got something weird which I was unable to figure out:
If I run this:
print hello . this,isatest, program
the output is:
hellothisisatestprogram
What I could understand is that it is treating both the text before and after the dot operator as string and concatenating them.
But what about the commas? Why is it getting omitted and not concatenated?
First period (.) is treated as concatenation operator. Subsequent commas separate multiple parameters of print. The result is the same - all parts are concatenated. If you want to print literal commas, enclose this,isatest, program in quotes - "this,isatest, program" to form single argument.
http://perldoc.perl.org/functions/print.html
I think this is what you want:
perl -e 'print "hello"." this,isatest,program"."\n"'
Run above code and check the output. If it gives you desired output then I guess we have an explanation.
I use the split function by two ways. First way (string argument to split):
my $string = "chr1.txt";
my #array1 = split(".", $string);
print $array1[0];
I get this error:
Use of uninitialized value in print
When I do split by the second way (regular expression argument to split), I don't get any errors.
my #array1 = split(/\./, $string); print $array1[0];
My first way of splitting is not working only for dot.
What is the reason behind this?
"\." is just ., careful with escape sequences.
If you want a backslash and a dot in a double-quoted string, you need "\\.". Or use single quotes: '\.'
If you just want to parse files and get their suffixes, better use the fileparse() method from File::Basename.
Additional details to the information provided by Mat:
In split "\.", ... the first parameter to split is first interpreted as a double-quoted string before being passed to the regex engine. As Mat said, inside a double-quoted string, a \ is the escape character, meaning "take the next character literally", e.g. for things like putting double quotes inside a double-quoted string: "\""
So your split gets passed "." as the pattern. A single dot means "split on any character". As you know, the split pattern itself is not part of the results. So you have several empty strings as the result.
But why is the first element undefined instead of empty? The answer lies in the documentation for split: if you don't impose a limit on the number of elements returned by split (its third argument) then it will silently remove empty results from the end of the list. As all items are empty the list is empty, hence the first element doesn't exist and is undefined.
You can see the difference with this particular snippet:
my #p1 = split "\.", "thing";
my #p2 = split "\.", "thing", -1;
print scalar(#p1), ' ', scalar(#p2), "\n";
It outputs 0 6.
The "proper" way to deal with this, however, is what #soulSurfer2010 said in his post.
So I thought this would just be a simple issue however I'm getting the incorrect results. Basically I am trying to remove the quotes around a string. For example I have the string "01:00" and I want 01:00, below is the code on how I thought I would be able to do this:
$expected_start_time = $conditions =~ m/(\"[^\"])/;
Every time this runs it returns 1, so I'm guessing that it is just returning true and not actually extracting the string from the quotes. This happen no matter what is in the quotes "02:00", "02:20", "08:00", etc.
All you forgot was parens for the LHS to put the match into list context so it returns the submatch group(s). The normal way to do this is:
($expected_start_time) = $condition =~ /"([^"]*)"/;
It appears that you know that the first and last character are quotes. If that is the case, use
$expected_start_time = substr $conditions, 1, -1;
No need for a regexp.
The brute force way is:
$expected_start_time = $conditions;
$expected_start_time =~ s/"//g;
Note that the original regex:
m/(\"[^\"])/
would capture the opening quote and the following non-quote character. To capture the non-quote characters between double quotes, you'd need some variant on:
m/"([^"]*)"/;
This being Perl (and regexes), TMTOWTDI - There's More Than One Way Do It.
In scalar context a regex returns true if the regex matches the string. You can access the match with $1. See perlre.
I'm trying to clean up form input using the following Perl transliteration:
sub ValidateInput {
my $input = shift;
$input =~ tr/a-zA-Z0-9_#.:;',#$%&()\/\\{}[]?! -//cd;
return $input;
}
The problem is that this transliteration is removing embedded newline characters that users may enter into a textarea field which I want to keep as part of the string. Any ideas on how I can update this to stop it from removing embedded newline characters? Thanks in advance for your help!
I'm not sure what you are doing, but I suspect you are trying to keep all the characters between the space and the tilde in the ASCII table, along with some of the whitespace characters. I think most of your list condenses to a single range \x20-\x7e:
$string =~ tr/\x0a\x0d\x20-\x7e//cd;
If you want to knock out a character like " (although I suspect you really want it since you allow the single quote), just adjust your range:
$string =~ tr/\x0a\x0d\x20-\xa7\xa9-\x7e//cd;
That's a bit of a byzantine way of doing it! If you add \012 it should keep the newlines.
$input =~ tr/a-zA-Z0-9_#.:;',#$%&()\/\{}[]?! \012-//cd;
See Form content types.
application/x-www-form-urlencoded: Line breaks are represented as "CR LF" pairs (i.e., %0D%0A).
...
multipart/form-data: As with all MIME transmissions, "CR LF" (i.e., %0D%0A) is used to separate lines of data.
I do not know what you have in the database. Now you know what your script it sees.
You are using CGI.pm, right?
Thanks for the help guys! Ultimately I decided to process all the data in our database to remove the character that was causing the issue so that any text that was submitted via our update form (and not changed by the user) would match what was in the database. Per your suggestions I also added a few additional allowed characters to the validation regex.