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Re: using sed buffers

by sauoq (Abbot)
on May 02, 2012 at 21:41 UTC ( #968554=note: print w/ replies, xml ) Need Help??


in reply to using sed buffers

So, your code probably actually looks like this:

s!.*pts/\(\[0-9\]\[0-9\]*\).*!\1!
Right? One point, s/// isn't "sed" ... it's "substitute". Now what do you really hope to do? And how are you calling it? If this you are doing this on a command line, how are you calling it exactly? ('Cuz there are better ways to quote than with all the slashes.) And what do you really mean that you want when you say "strip the tty off"?

-sauoq
"My two cents aren't worth a dime.";


Comment on Re: using sed buffers
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Re^2: using sed buffers
by floobit (Initiate) on May 02, 2012 at 21:46 UTC

    Full code. I am attempting to get a list of the ttys associated with the running user. This is the first step.

    #!/usr/bin/perl -w use strict; my $user=`whoami`; my @ps=`ps aux |grep $user`; #print @ps; foreach(@ps){ $_ =~ s!.*pts/\([0-9][0-9]*\).*!$1!; print $_; } exit 0

      I see. You want something like:

      for (@ps){ m!.*pts/([0-9]+)! and print $1; }

      Update:

      It'd be better without the .*, actually. With it, it would fail if the user in question were running a command that included the string pts/999999 because it would find the last one rather than the first.

      Also, you might want to think about stuff like sshd: username@pts/1234 showing up in the commands. It's probably better to get the TTY from the right column rather than use a regex.

      Update 2:

      A couple quick points about what you were using and why not to do it that way...

      $_ =~ s!.*pts/\([0-9][0-9]*\).*!$1!
      Backwhacking your parens means to match actual parens, not to capture what's between them. Also, * means 0 or more and + means 1 or more, so [0-9][0-9]* is just a longer way of saying [0-9]+. Finally, there's no point in substituting out everything that doesn't match your captured parts when you can just print the captured part instead.

      Oh, and you don't have to be explicit about working on $_ ... being able to use it implicitly is kind of its point.

      -sauoq
      "My two cents aren't worth a dime.";
Re^2: using sed buffers
by JavaFan (Canon) on May 02, 2012 at 22:48 UTC
    One point, s/// isn't "sed" ... it's "substitute".
    Perl, of course, got its s/// from sed...
      Perl, of course, got its s/// from sed...

      Of course. And even in sed, s/// means "substitute".

      -sauoq
      "My two cents aren't worth a dime.";

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