Removing extra pipes and text around them from string in Perl with regex

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Let's say I have a string like this that I'd like to process in perl.

hello|world|nice|to|meet|you

I'd like to keep the first three pipe symbols and the text around them and discard the rest of the string. So, I'd end up with this:

hello|world|nice|to

I'm thinking I want to do something like this:

substitute (zero or more non-pipes followed by a pipe)[3 times] followed by the rest of the string with a back reference to the piece of the regex where I matched the 3 pipes and the characters around them. 

I'm not sure about the regex syntax for this in perl.

I can do what I want to like this:

$str = "hello|world|nice|to|meet|you" ;
@a = split(/\|/, $str) ;
print $a[0] . "|" . $a[1] . "|" . $a[2] . "|" . $a[3]

But, I'd like to see how to do this with a regex.

regex, perl regular expression take out text enclosed in parentheses I am current using this but it's not working: $str =~ s/( ( [^)]+ ) )//;. Thanks! To remove the space you can simply remove spaces before the parenthesis. Converts "This is a (extra stuff) string" to "This is a string", leaving two spaces between the "a" and " string". In some other languages there are functions called ltrim and rtrim to remove spaces and tabs from the beginning and from the end of a string respectively. Sometimes they even have a function called trim to remove white-spaces from both ends of a string.

You can capture with ():

$ cat foo.pl && ./foo.pl
#!/usr/bin/perl

$str = "hello|world|nice|to|meet|you" ;
$str =~ s/^(([^\|]*\|){3}[^\|]*)\|.*/$1/;
print STDOUT "$str\n";
hello|world|nice|to

Perl split - to cut up a string into pieces, split REGEX, STRING will split the STRING at every match of the We want to split where the = sign and disregard the spaces around it. The right way to split on a pipe | character is to escape the special regex character: It is also a critical part of the example showing how to count words in a text file. Your description is a bit vague. I assume that you have a perl variable that happens to have double quote characters inside it, though why that would be needed in XML is a bit beyond me (XML is its own delimiter, and shouldn't need extra ones). Removing double quotes from around a Perl string is pretty easy:

To remove all but the first 3 pipes and surrounding text can be done like :

$txt =~ s/^(?:[^|]*\|){3}[^|]*\K.*//s;

[PDF] Regular Expressions: The Complete Tutorial, A regular expression (regex or regexp for short) is a special text string for This syntax is supported by the JGsoft engine, Perl and d\d� is a step ahead, though it will still match „19/39/99”. Replace method will remove the regex match from the string, and insert the Alternation with The Vertical Bar or Pipe Symbol. string parsing (for example catch all URL GET parameters, capture text inside a set of parenthesis) string replacement (for example, even during a code session using a common IDE to translate a

Perl Tutorial: Regular Expressions (Regex), File IO and Text , Text Processing. Perl is famous for processing text files via regular expressions . You can use matching operator m// to check if a regex pattern exists in a string . The syntax is: variable $_ . It returns true if $_ matches regex; and false otherwise. my $reply; chomp($reply = <>); # Remove newline print $reply =~ /^ y/i ? extra (X) single line (s) Remove Space(s) Remove spaces at the beginning and the end of a string but not removing spaces between words. Regex Tester isn't

1. Strings - Perl Cookbook, 2nd Edition [Book], A string in Perl is not an array of characters—nor of bytes, for that matter. Most are interpolated by default, such as in patterns ( /regex/ ) and running commands ( $x = `cmd` ). be careful with those three: they're strictly byte-oriented, and moving around It removes leading whitespace from the text of the here document. (BTW now you can see why adding the single-quotes around the printed values is useful as you can see the captured white spaces.) So let's say say that before the actual string we want either a white-space \s or that it will be the beginning of the string ^. We wrap them in a pair of parentheses and make this an alternation: (^|\s).

perlre, Regular expressions are strings with the very particular syntax and meaning described in but it is important when you are capturing matched text using parentheses. And use of re 'strict' adds extra checking to catch some typos that might (Older programs did this by setting $* , but this option was removed in perl 5.10.). A here-document allows you to create a string that spreads on multiple lines and preserves white spaces and new-lines. If you run the following code it will print exactly what you see starting from the word Dear till the line before the second appearance of END_MESSAGE.

Comments
  • You are using a regex :)
  • join "|", ( split /\|/ )[0..3]
  • Yes, split with a regex.