Re: [OT] Perl: exec and $variables
On Sat, Jul 21, 2001 at 04:53:35PM +0200, Joost Kooij wrote: What is the need for the seperate variable $BEGINREGEX? It complicates things enormously when you want a variable $no to be evaluated whenever $BEGINREGEX is evaluated. The only sane way out is to completely reevaluate $BEGINREGEX after each change to $no. To do that successfully, you have to escape '$', '', and '\' and then escape some of the escapes, but others not, depending on wheter they should never be expanded, expanded in the eval or expanded when applying the regexp. I wouldn't touch that with a ten foot pole if I were you. If you succeed at it, you have great job security, and a maintenance nightmare. Right, I agree. Easier is to not use a $BEGINREGEX at all: $line =~ m(^!-- // begin of news$no // !--$); should always work, for the current value of $no. Which is what I ended up doing. I made a function getBeginRegex() and getEndRegex() which return the string I then use as a regex for searching. This way I don't have to write the regex string many times over in the program, which is what I was trying to avoid when I did the $BEGINREGEX thing. Thanks a lot for your help! Sven
Re: [OT] Perl: exec and $variables
On Sat, Jul 21, 2001 at 10:36:55AM -0500, Andrew Perrin wrote:
my $template = '^!-- // begin of news%no% // !--$';
my $no = 99;
my $bla = $template;
$bla =~ s/%no%/$no/g;
$replace{no} = 99;
$bla =~ s/%(.+?)%/$replace{$1}/g;
Disclaimer: these are trivial and not terribly robust solutions; take them
as a starting point, not a complete solution.
I didn't do things your way, but I can always re-use your ideas sometime
later. :-)
Thanks for your help!
Sven
[OT] Perl: exec and $variables
Hello I have a problem with some perl code. I know this is off-topic, but there are numerous knowledgeable people on deb-usr, so forgive me for posting this. Now to my problem. Given the following variable, my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\); the following eval() call doesn't substitute $no for what it is and return the new string with the substituted $no in it: my $no = 1; my $bla = eval($BEGINREGEX); print $bla\n; $bla is empty for some reason. So how would I go about having $no substituted in $BEGINREGEX for whatever it happens to be set to at a particular point in the script? Cheers! Sven -- The best way to escape from a problem is to solve it.
Re: [OT] Perl: exec and $variables
On Sat, Jul 21, 2001 at 01:04:40PM +0200, Sven Burgener wrote: I have a problem with some perl code. I know this is off-topic, but there are numerous knowledgeable people on deb-usr, so forgive me for posting this. Now to my problem. Given the following variable, my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\); Please tell us what you're trying to accomplish first. It is unclear what assumptions you are making. the following eval() call doesn't substitute $no for what it is and return the new string with the substituted $no in it: my $no = 1; my $bla = eval($BEGINREGEX); print $bla\n; $bla is empty for some reason. So how would I go about having $no substituted in $BEGINREGEX for whatever it happens to be set to at a particular point in the script? You probably do not want to use eval here, or at least not in this way. Cheers, Joost
Re: [OT] Perl: exec and $variables
On Sat, Jul 21, 2001 at 01:46:25PM +0200, Joost Kooij wrote: On Sat, Jul 21, 2001 at 01:04:40PM +0200, Sven Burgener wrote: my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\); Please tell us what you're trying to accomplish first. It is unclear what assumptions you are making. What I want is the variable $BEGINREGEX to contain a string like so: ^!-- // begin of news1 // !--$ or ^!-- // begin of news2 // !--$ The digit after the news should be whatever $no is set to at that point in the script. my $no = 1; my $bla = eval($BEGINREGEX); print $bla\n; $bla is empty for some reason. You probably do not want to use eval here, or at least not in this way. What should I do then? It's simple, really. I am sure I am just making a stupid mistake. my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\); my $no = 99; my $bla = eval($BEGINREGEX); print regex string: $bla\n; What should be printed: regex string: ^!-- // begin of news99 // !--$ But it isn't, so what am I doing wrong here? Cheers, Sven -- The best way to escape from a problem is to solve it.
Re: [OT] Perl: exec and $variables
eval() doesn't do what you want - it *executes* code, as opposed to
substituting values for variables. Try something like:
my $template = '^!-- // begin of news%no% // !--$';
my $no = 99;
my $bla = $template;
$bla =~ s/%no%/$no/g;
You can get fancy too, if you want:
$replace{no} = 99;
$bla =~ s/%(.+?)%/$replace{$1}/g;
now anything encased in % signs will be replaced by the associated value
in the %replace hash.
Disclaimer: these are trivial and not terribly robust solutions; take them
as a starting point, not a complete solution.
--
Andrew J Perrin - [EMAIL PROTECTED] - http://www.unc.edu/~aperrin
Assistant Professor of Sociology, U of North Carolina, Chapel Hill
269 Hamilton Hall, CB#3210, Chapel Hill, NC 27599-3210 USA
On Sat, 21 Jul 2001, Sven Burgener wrote:
On Sat, Jul 21, 2001 at 01:46:25PM +0200, Joost Kooij wrote:
On Sat, Jul 21, 2001 at 01:04:40PM +0200, Sven Burgener wrote:
my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\);
Please tell us what you're trying to accomplish first. It is unclear
what assumptions you are making.
What I want is the variable $BEGINREGEX to contain a string like so:
^!-- // begin of news1 // !--$
or
^!-- // begin of news2 // !--$
The digit after the news should be whatever $no is set to at that
point in the script.
my $no = 1;
my $bla = eval($BEGINREGEX);
print $bla\n;
$bla is empty for some reason.
You probably do not want to use eval here, or at least not in this way.
What should I do then?
It's simple, really. I am sure I am just making a stupid mistake.
my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\);
my $no = 99;
my $bla = eval($BEGINREGEX);
print regex string: $bla\n;
What should be printed:
regex string: ^!-- // begin of news99 // !--$
But it isn't, so what am I doing wrong here?
Cheers,
Sven
--
The best way to escape from a problem is to solve it.
--
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Re: [OT] Perl: exec and $variables
On Sat, Jul 21, 2001 at 02:31:58PM +0200, Sven Burgener wrote: On Sat, Jul 21, 2001 at 01:46:25PM +0200, Joost Kooij wrote: On Sat, Jul 21, 2001 at 01:04:40PM +0200, Sven Burgener wrote: my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\); Please tell us what you're trying to accomplish first. It is unclear what assumptions you are making. What I want is the variable $BEGINREGEX to contain a string like so: ^!-- // begin of news1 // !--$ or ^!-- // begin of news2 // !--$ The digit after the news should be whatever $no is set to at that point in the script. You are still not telling really what you want to accomplish, but I infer that you want to match lines like: !-- // begin of news1 // !-- To test if the entire $line matches it, you would write: $line =~ m(^!-- // begin of news1 // !--$); Notice that I used the m operator explicitly, so I can use an alternate regexp delimiter, or else I would have had to escape each of the slashes in your pattern. What is the need for the seperate variable $BEGINREGEX? It complicates things enormously when you want a variable $no to be evaluated whenever $BEGINREGEX is evaluated. The only sane way out is to completely reevaluate $BEGINREGEX after each change to $no. To do that successfully, you have to escape '$', '', and '\' and then escape some of the escapes, but others not, depending on wheter they should never be expanded, expanded in the eval or expanded when applying the regexp. I wouldn't touch that with a ten foot pole if I were you. If you succeed at it, you have great job security, and a maintenance nightmare. Easier is to not use a $BEGINREGEX at all: $line =~ m(^!-- // begin of news$no // !--$); should always work, for the current value of $no. my $no = 1; my $bla = eval($BEGINREGEX); print $bla\n; $bla is empty for some reason. You probably do not want to use eval here, or at least not in this way. What should I do then? It's simple, really. I am sure I am just making a stupid mistake. my $BEGINREGEX = sprintf(\^!-- // begin of news\$no // !--\$\); my $no = 99; my $bla = eval($BEGINREGEX); print regex string: $bla\n; What should be printed: regex string: ^!-- // begin of news99 // !--$ Why are you putting the sprintf in the regexp at all? The '^' and '$' anchors only work when at the begin, resp. at the end of the whole regexp. I think that the use of sprintf is unnecessary, and even complicates things enormously. But it isn't, so what am I doing wrong here? AFAICS, you're just not doing it in the most straightforward way. Try to use fixed regexps, and leave the $no in it, so it will be expanded every time perl uses the regexp. Cheers, Joost
