Beefy Boxes and Bandwidth Generously Provided by pair Networks
"be consistent"
 
PerlMonks  

comment on

( [id://3333]=superdoc: print w/replies, xml ) Need Help??

Dear Monks

Following the suggestions I had from this node, I started coding a one liner but I can't get it to work.

The problem: I have a UNIX alias file and I want to modify only root's alias, and only if it is different from a predefined one. For example:

  • root: admin@somewhere.here is OK and should be left untouched
  • root: someone@somewhere.else is NOT OK and should be modified
  • Any non-root alias should be left untouched

To test if I well understanded the lesson, I created a file containing...

root: admin@somewhere.here root: someone@somewhere.else any: anybody@anywhere.else

...and wrote a regular expression that I would eventually put into an s/// operator; I expected it to match just the second line, but the one-liner below...

perl -ne '/^root:\s*(?!admin@somewhere.here)/ and print' alliases

actually outputs:

root: admin@somewhere.here root: someone@somewhere.else

which looks quite odd to me, since I expected the first line not to match. I also tried quoting the @ sign with a backslash, \Q...\E or useing strict: no way. More oddly (to me), if I add a \s*$ at the end of the regex to match any whitespace between the address and the end of line, then no line matches!!!

I am getting a little confused, where am I doing wrong?

Thanks in advance, and thanks to everyone that answered to the original post

Ciao!
--bronto


The very nature of Perl to be like natural language--inconsistant and full of dwim and special cases--makes it impossible to know it all without simply memorizing the documentation (which is not complete or totally correct anyway).
--John M. Dlugosz

In reply to On zero-width negative lookahead assertions by bronto

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this?Last hourOther CB clients
Other Users?
Others taking refuge in the Monastery: (3)
As of 2024-04-25 18:48 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found