FAQ 4.32 How do I strip blank space from the beginning/end of a string?

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

------------------------------------------------------------ --------

4.32: How do I strip blank space from the beginning/end of a string?

(contributed by brian d foy)

A substitution can do this for you. For a single line, you want to
replace all the leading or trailing whitespace with nothing. You can do
that with a pair of substitutions.

s/^\s+//;
s/\s+$//;

You can also write that as a single substitution, although it turns out
the combined statement is slower than the separate ones. That might not
matter to you, though.

s/^\s+|\s+$//g;

In this regular expression, the alternation matches either at the
beginning or the end of the string since the anchors have a lower
precedence than the alternation. With the "/g" flag, the substitution
makes all possible matches, so it gets both. Remember, the trailing
newline matches the "\s+", and the "$" anchor can match to the physical
end of the string, so the newline disappears too. Just add the newline
to the output, which has the added benefit of preserving "blank"
(consisting entirely of whitespace) lines which the "^\s+" would remove
all by itself.

while( <> )
{
s/^\s+|\s+$//g;
print "$_\n";
}

For a multi-line string, you can apply the regular expression to each
logical line in the string by adding the "/m" flag (for "multi-line").
With the "/m" flag, the "$" matches *before* an embedded newline, so it
doesn't remove it. It still removes the newline at the end of the
string.

$string =~ s/^\s+|\s+$//gm;

Remember that lines consisting entirely of whitespace will disappear,
since the first part of the alternation can match the entire string and
replace it with nothing. If need to keep embedded blank lines, you have
to do a little more work. Instead of matching any whitespace (since that
includes a newline), just match the other whitespace.

$string =~ s/^[\t\f ]+|[\t\f ]+$//mg;



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Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

"PerlFAQ Server" wrote in message
news:64spn4-1kn.ln1@blue.stonehenge.com...
....
> 4.32: How do I strip blank space from the beginning/end of a string?
>
> (contributed by brian d foy)
>
> A substitution can do this for you. For a single line, you want to
> replace all the leading or trailing whitespace with nothing. You can do
> that with a pair of substitutions.
>
> s/^\s+//;
> s/\s+$//;

This is such a common task that I think it would be
worthwhile to have a dedicated, more efficient command
for it, similar to chomp/chop.

And what would be a good name for the command?

Mario

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

"Mario D'Alessio" writes:

> "PerlFAQ Server" wrote in message
> news:64spn4-1kn.ln1@blue.stonehenge.com...
>> s/^\s+//;
>> s/\s+$//;
>
> This is such a common task that I think it would be
> worthwhile to have a dedicated, more efficient command
> for it, similar to chomp/chop.
>
> And what would be a good name for the command?

"trim"

It's already in countless CPAN modules. Seems to me it was so
worthwhile to have a dedicated command that many authors wrote
one themselves.

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

On Wed, 1 Aug 2007 13:55:44 -0500, "Mario D'Alessio"
wrote:

>> s/^\s+//;
>> s/\s+$//;
>
>This is such a common task that I think it would be
>worthwhile to have a dedicated, more efficient command
>for it, similar to chomp/chop.

I don't think so. That would be much in the php philosophy. Perl is
already a "large" language, but it still provides relatively simple
tools that linked together make for a synergic effect.

And as for efficiency... is the provided solution not fast enough? I
can't imagine many situations in which this would matter.

>And what would be a good name for the command?

stripwhitespace() ?


Michele
--
{$_=pack'B8'x25,unpack'A8'x32,$a^=sub{pop^pop}->(map substr
(($a||=join'',map--$|x$_,(unpack'w',unpack'u','G^ ..'KYU;*EVH[.FHF2W+#"\Z*5TI/ER 256),7,249);s/[^\w,]/ /g;$ \=/^J/?$/:"\r";print,redo}#JAPH,

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

"Michele Dondi" wrote in message
news:sfd3b3lfnphuk3qa9vked52olhd108e02f@4ax.com...
> On Wed, 1 Aug 2007 13:55:44 -0500, "Mario D'Alessio"
> wrote:
>
>>> s/^\s+//;
>>> s/\s+$//;
>>
>>This is such a common task that I think it would be
>>worthwhile to have a dedicated, more efficient command
>>for it, similar to chomp/chop.
>
> I don't think so. That would be much in the php philosophy. Perl is
> already a "large" language, but it still provides relatively simple
> tools that linked together make for a synergic effect.
>
> And as for efficiency... is the provided solution not fast enough? I
> can't imagine many situations in which this would matter.

I never timed it, but I wondered if the processing of a
regex makes it less efficient than a dedicated command
similar to chomp.

Mario

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

On Thu, 2 Aug 2007 10:47:01 -0500, "Mario D'Alessio"
wrote:

>> And as for efficiency... is the provided solution not fast enough? I
>> can't imagine many situations in which this would matter.
>
>I never timed it, but I wondered if the processing of a
>regex makes it less efficient than a dedicated command
>similar to chomp.

The general answer is that you should not care, and if you do care
then you shouldn't program in Perl. If you're really concerned you may
try writing an XS version of your command and benchmark it along with
the regex based one.


Ciao,
Michele
--
{$_=pack'B8'x25,unpack'A8'x32,$a^=sub{pop^pop}->(map substr
(($a||=join'',map--$|x$_,(unpack'w',unpack'u','G^ ..'KYU;*EVH[.FHF2W+#"\Z*5TI/ER 256),7,249);s/[^\w,]/ /g;$ \=/^J/?$/:"\r";print,redo}#JAPH,

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

I'm wondering how many perl programmers have always-include
libraries of useful functions, one of them being "trim".

So, have a poll, and decide based on that.

David

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

dkcombs@panix.com (David Combs) writes:

> I'm wondering how many perl programmers have always-include
> libraries of useful functions, one of them being "trim".

We all do - it's called "CPAN".

sherm--

--
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Cocoa programming in Perl: http://camelbones.sourceforge.net

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

Sherm Pendley wrote:
> dkcombs@panix.com (David Combs) writes:
>
>> I'm wondering how many perl programmers have always-include
>> libraries of useful functions, one of them being "trim".
>
> We all do - it's called "CPAN".
>
> sherm--
Yes, you are right sherm ;-) But, frankly speaking, the trim() is the
function which absent in Perl. Everytime I write script for string
manupulation and I plan to write more then 50 lines I write this

sub trim
{
my $t = shift;
$t =~s/^\s*|\s*$//sg;
return $t;
}

sub ltrim
{
my $t = shift;
$t =~s/^\s*//s;
return $t;
}

sub rtrim
{
my $t = shift;
$t =~s/\s*$//s;
return $t;
}

--

Petr Vileta, Czech republic
(My server rejects all messages from Yahoo and Hotmail. Send me your mail
from another non-spammer site please.)

Re: FAQ 4.32 How do I strip blank space from the beginning/end of astring?

>>>>> "PV" == Petr Vileta writes:

PV> sub trim
PV> {
PV> my $t = shift;
PV> $t =~s/^\s*|\s*$//sg;

that is known to be slower than doing left and right trim in separate
operations. google for this and you will see plenty of benchmarks

the /s modifier is useless as you don't use . in the regex.

replacing \s* will happen for every string which is wasteful. use \s+ so
you only replace when you have at least one \s.

PV> sub ltrim
PV> {
PV> my $t = shift;
PV> $t =~s/^\s*//s;
PV> return $t;
PV> }

PV> sub rtrim
PV> {
PV> my $t = shift;
PV> $t =~s/\s*$//s;
PV> return $t;
PV> }

the above comments apply to those as well except for the using two s///
ops.

if you use those subs a lot (and i never seem to need them) you might as
well write them well so they run faster.

uri

--
Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org

Re: FAQ 4.32 How do I strip blank space from the beginning/end ofa string?

David Combs wrote:
> I'm wondering how many perl programmers have always-include
> libraries of useful functions, one of them being "trim".

I almost always use String::Strip for that.

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

On Sat, 1 Sep 2007 21:42:57 +0000 (UTC), dkcombs@panix.com (David
Combs) wrote:

>I'm wondering how many perl programmers have always-include
>libraries of useful functions, one of them being "trim".
>
>So, have a poll, and decide based on that.

First of all, please quote some context... inter alia this is a very
old thread... it would help. Coming to your question, it depends:
people use CPAN and own modules all the time, and not only for very
complex stuff that would require thousands of lines of code, but even
simpler things. One example that springs to mind is given by
List::Util's functions: I'm increasingly willing to to use the module
even if I just need one or two of them in one or two places in a tiny
script, and I'm not concerned with "efficiency". Similarly with e.g.
File::Basename. But as far as the hypothetical trim() function goes:
well, for one thing I've not needed it that often, and no, I wouldn't
probably use a library for it but stick to a plain

s/^\s+//, s/\s+$// for $string; # instead


My two eurocents,
Michele
--
{$_=pack'B8'x25,unpack'A8'x32,$a^=sub{pop^pop}->(map substr
(($a||=join'',map--$|x$_,(unpack'w',unpack'u','G^ ..'KYU;*EVH[.FHF2W+#"\Z*5TI/ER 256),7,249);s/[^\w,]/ /g;$ \=/^J/?$/:"\r";print,redo}#JAPH,

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

On Sun, 2 Sep 2007 04:44:25 +0200, "Petr Vileta"
wrote:

>Yes, you are right sherm ;-) But, frankly speaking, the trim() is the
>function which absent in Perl. Everytime I write script for string
>manupulation and I plan to write more then 50 lines I write this

I don't want to distrust you, but I'm astonished... I just happen not
to need this kinda things so often.


Michele
--
{$_=pack'B8'x25,unpack'A8'x32,$a^=sub{pop^pop}->(map substr
(($a||=join'',map--$|x$_,(unpack'w',unpack'u','G^ ..'KYU;*EVH[.FHF2W+#"\Z*5TI/ER 256),7,249);s/[^\w,]/ /g;$ \=/^J/?$/:"\r";print,redo}#JAPH,

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

Michele Dondi wrote:
> On Sun, 2 Sep 2007 04:44:25 +0200, "Petr Vileta"
> wrote:
>
>> Yes, you are right sherm ;-) But, frankly speaking, the trim() is the
>> function which absent in Perl. Everytime I write script for string
>> manupulation and I plan to write more then 50 lines I write this
>
> I don't want to distrust you, but I'm astonished... I just happen not
> to need this kinda things so often.
>
>
> Michele
Characteristic case is web form and putting fields to database. For example
user name, address or phone number. Many users type some like
" John Doe"
"Victory str. 60, London "
"+420 220 130 150"
Before I put these data to database I want to "normalise" it for future
comparing for duplicity.

" John Doe"
and
"John Doe"
is not the same for computer but is the same for human. So I must replace
all "more spaces" with "single space", and remove leading and trailing
spaces. Phone number must be a number not a string, so
"+420 220 130 150"
must be translated to
"420220130150"

--

Petr Vileta, Czech republic
(My server rejects all messages from Yahoo and Hotmail. Send me your mail
from another non-spammer site please.)

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

On Sat, 1 Sep 2007 21:42:57 +0000 (UTC), dkcombs@panix.com (David Combs) wrote:

>I'm wondering how many perl programmers have always-include
>libraries of useful functions, one of them being "trim".
>
>So, have a poll, and decide based on that.
>
>David
>

It would appear that a useful library may be fashioned out of
the MFC CString class, which has all the goodies. Trivial but usefull.

or try this:

TrimTheFat
{
my $string_ref = @_;
$$string_ref =~ s/^\s+//;
$$string_ref =~ s/\s+$//;
# add other fat trimming you would like
# ie: double slashes, double periods, etc..
}

my $fatstring = "This here is a fat string";
TrimTheFat ( \$fatstring);

Re: FAQ 4.32 How do I strip blank space from the beginning/end of astring?

>>>>> "s" == sln writes:

s> or try this:

why should we try it? it has a major bug. and it isn't valid perl.

s> TrimTheFat

no sub

s> {
s> my $string_ref = @_;

that doesn't assign what you think it does

s> $$string_ref =~ s/^\s+//;
s> $$string_ref =~ s/\s+$//;
s> # add other fat trimming you would like
s> # ie: double slashes, double periods, etc..

those would be options and not useful for a fast white space trimmer.

s> }

like michele said, this is too trivial to need a sub or a library.

uri

--
Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

On 2007-09-03 03:17:24 +0200, Uri Guttman said:

>>>>>> "s" == sln writes:
>
> s> or try this:
>
> why should we try it? it has a major bug. and it isn't valid perl.
>
> s> TrimTheFat
>
> no sub
>
> s> {
> s> my $string_ref = @_;
>
> that doesn't assign what you think it does
>
> s> $$string_ref =~ s/^\s+//;
> s> $$string_ref =~ s/\s+$//;
> s> # add other fat trimming you would like
> s> # ie: double slashes, double periods, etc..
>
> those would be options and not useful for a fast white space trimmer.
>
> s> }

Also, there's no need to use a reference:

sub trim { s/^\s+//, s/\s+$// for shift }

> like michele said, this is too trivial to need a sub or a library.

That too.

Anno
>

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

Petr Vileta schreef:

> sub trim {
> my $t = shift;
> $t =~s/^\s*|\s*$//sg;
> return $t;
> }

Please read `perldoc -q space`.

The '*' quantifier should be '+'. The /s modifier should not be there.
The substitution is faster when split up, then the /g modifier is also
gone.


Variant:

sub trim { s/^\s+//, s/\s+$// for @_ }

but beware that this will change the parameter(s) themselves.


(the same comments go for the rest)

--
Affijn, Ruud

"Gewoon is een tijger."

Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?

Dr.Ruud wrote:
> Petr Vileta schreef:
>
>> sub trim {
>> my $t = shift;
>> $t =~s/^\s*|\s*$//sg;
>> return $t;
>> }
>
> Please read `perldoc -q space`.
>
> The '*' quantifier should be '+'. The /s modifier should not be there.
> The substitution is faster when split up, then the /g modifier is also
> gone.
>
Yes, a quantifier I had bad, but /s modifier I must use because
" abcd\n efgh\n "
must return
"abcd\n efgh"
This is for input from field.<br /> <br /> ><br /> > Variant:<br /> ><br /> > sub trim { s/^\s+//, s/\s+$// for @_ }<br /> ><br /> > but beware that this will change the parameter(s) themselves.<br /> ><br /> Thanks, this is better. I don't know why I not use syntax "do_somethig for <br /> ...." :-)<br /> <br /> -- <br /> <br /> Petr Vileta, Czech republic<br /> (My server rejects all messages from Yahoo and Hotmail. Send me your mail <br /> from another non-spammer site please.)</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 03.09.2007 15:09:04 von Petr Vileta</span> <p>Anno Siegel wrote:<br /> > On 2007-09-03 03:17:24 +0200, Uri Guttman <uri@stemsystems.com> said:<br /> ><br /> >> like michele said, this is too trivial to need a sub or a library.<br /> ><br /> > That too.<br /> ><br /> As the case may be ;-) When you remove blanks 50 times in 50kb source code <br /> then is better to use sub or library.<br /> <br /> -- <br /> <br /> Petr Vileta, Czech republic<br /> (My server rejects all messages from Yahoo and Hotmail. Send me your mail <br /> from another non-spammer site please.)</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 03.09.2007 15:32:11 von Peter Makholm</span> <p>"Petr Vileta" <stoupa@practisoft.cz> writes:<br /> <br /> >> The '*' quantifier should be '+'. The /s modifier should not be there.<br /> >> The substitution is faster when split up, then the /g modifier is also<br /> >> gone.<br /> >><br /> > Yes, a quantifier I had bad, but /s modifier I must use because<br /> > " abcd\n efgh\n "<br /> > must return<br /> > "abcd\n efgh"<br /> > This is for input from <textarea> field.<br /> <br /> I don't think the /s modifier does what you believe. At least it looks<br /> like it works as you want without the modifier:<br /> <br /> $ cat > test_trim.pl<br /> sub trim { s/^\s+//, s/\s+$// for @_ };<br /> $a = " abcd\n efgh\n ";<br /> print "[[$a]]";<br /> trim $a;<br /> print "[[$a]]"'<br /> $ perl -l test_trim.pl<br /> [[ abcd<br /> efgh<br /> ]]<br /> [[abcd<br /> efgh]]<br /> $<br /> <br /> Unless you fiddle with $* (which you under no circumstances should do)<br /> the /s-modifier should only change the semantics of ".".<br /> <br /> //Makholm</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 03.09.2007 15:34:42 von Ben Morrow</span> <p>Quoth "Petr Vileta" <stoupa@practisoft.cz>:<br /> > Dr.Ruud wrote:<br /> > > Petr Vileta schreef:<br /> > ><br /> > >> sub trim {<br /> > >> my $t = shift;<br /> > >> $t =~s/^\s*|\s*$//sg;<br /> > >> return $t;<br /> > >> }<br /> > ><br /> > > Please read `perldoc -q space`.<br /> > ><br /> > > The '*' quantifier should be '+'. The /s modifier should not be there.<br /> > > The substitution is faster when split up, then the /g modifier is also<br /> > > gone.<br /> > ><br /> > Yes, a quantifier I had bad, but /s modifier I must use because<br /> > " abcd\n efgh\n "<br /> > must return<br /> > "abcd\n efgh"<br /> <br /> Did you try it without /s? The *only* thing /s affects is the behaviour<br /> of '.'. You have no '.'s in your regex, so /s makes no difference.<br /> <br /> Ben</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 03.09.2007 15:36:13 von Tad McClellan</span> <p>Petr Vileta <stoupa@practisoft.cz> wrote:<br /> > Dr.Ruud wrote:<br /> >> Petr Vileta schreef:<br /> <br /> <br /> >>> $t =~s/^\s*|\s*$//sg;<br /> <br /> >> The /s modifier should not be there.<br /> <br /> > but /s modifier I must use <br /> <br /> <br /> If you think so, then you do not yet understand what /s does.<br /> <br /> It makes dot match a newline.<br /> <br /> It therefore has no effect at all when your pattern does not contain a dot.<br /> <br /> Your pattern does not contain a dot, so the /s modifier should not be there.<br /> <br /> <br /> -- <br /> Tad McClellan<br /> email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 03.09.2007 15:45:10 von Peter Makholm</span> <p>Ben Morrow <ben@morrow.me.uk> writes:<br /> <br /> > Did you try it without /s? The *only* thing /s affects is the behaviour<br /> > of '.'. You have no '.'s in your regex, so /s makes no difference.<br /> <br /> The /s-modifier withou the /m-modifier also forces ^ and $ to mean<br /> beginning and end of string no matter what $* is. But you shouldn't<br /> use $* so for every sane piece of code you're right.<br /> <br /> //Makholm</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of astring?</h2><span>am 03.09.2007 21:17:19 von Uri Guttman</span> <p>>>>>> "PM" == Peter Makholm <peter@makholm.net> writes:<br /> <br /> PM> Ben Morrow <ben@morrow.me.uk> writes:<br /> >> Did you try it without /s? The *only* thing /s affects is the behaviour<br /> >> of '.'. You have no '.'s in your regex, so /s makes no difference.<br /> <br /> PM> The /s-modifier withou the /m-modifier also forces ^ and $ to mean<br /> PM> beginning and end of string no matter what $* is. But you shouldn't<br /> PM> use $* so for every sane piece of code you're right.<br /> <br /> /s and /m are independent so i wouldn't use the word 'forces'. the<br /> behavior of ^ and $ are not affected by /s.<br /> <br /> uri<br /> <br /> -- <br /> Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com<br /> --Perl Consulting, Stem Development, Systems Architecture, Design and Coding-<br /> Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of astring?</h2><span>am 03.09.2007 23:02:19 von Ben Morrow</span> <p>Quoth Uri Guttman <uri@stemsystems.com>:<br /> > >>>>> "PM" == Peter Makholm <peter@makholm.net> writes:<br /> > <br /> > PM> Ben Morrow <ben@morrow.me.uk> writes:<br /> > >> Did you try it without /s? The *only* thing /s affects is the behaviour<br /> > >> of '.'. You have no '.'s in your regex, so /s makes no difference.<br /> > <br /> > PM> The /s-modifier withou the /m-modifier also forces ^ and $ to mean<br /> > PM> beginning and end of string no matter what $* is. But you shouldn't<br /> > PM> use $* so for every sane piece of code you're right.<br /> > <br /> > /s and /m are independent so i wouldn't use the word 'forces'. the<br /> > behavior of ^ and $ are not affected by /s.<br /> <br /> No, bizarrely enough Peter seems to be correct, in that iff $* is set /s<br /> affects ^ and $ as well, undoing the effects of setting $*:<br /> <br /> $ perl -le'$* = 1; $_ = "\nfoo"; print /^foo/; print /^foo/s;'<br /> 1<br /> <br /> $ <br /> <br /> However, this is clearly a silly edge case, as the whole point of /sm is<br /> to remove the need to ever set $*.<br /> <br /> Ben</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of astring?</h2><span>am 04.09.2007 00:24:10 von Uri Guttman</span> <p>>>>>> "BM" == Ben Morrow <ben@morrow.me.uk> writes:<br /> <br /> BM> Quoth Uri Guttman <uri@stemsystems.com>:<br /> >> >>>>> "PM" == Peter Makholm <peter@makholm.net> writes:<br /> >> <br /> PM> Ben Morrow <ben@morrow.me.uk> writes:<br /> >> >> Did you try it without /s? The *only* thing /s affects is the behaviour<br /> >> >> of '.'. You have no '.'s in your regex, so /s makes no difference.<br /> >> <br /> PM> The /s-modifier withou the /m-modifier also forces ^ and $ to mean<br /> PM> beginning and end of string no matter what $* is. But you shouldn't<br /> PM> use $* so for every sane piece of code you're right.<br /> >> <br /> >> /s and /m are independent so i wouldn't use the word 'forces'. the<br /> >> behavior of ^ and $ are not affected by /s.<br /> <br /> BM> No, bizarrely enough Peter seems to be correct, in that iff $* is set /s<br /> BM> affects ^ and $ as well, undoing the effects of setting $*:<br /> <br /> but that isn't what he said. he said /s without /m FORCES ^ and $ no<br /> matter the setting of $*. so i said it doesn't as /s has no effect on ^<br /> and $ and disregarded $* as it is deprecated and was a very silly<br /> variable that larry deeply regrets creating. :)<br /> <br /> BM> $ perl -le'$* = 1; $_ = "\nfoo"; print /^foo/; print /^foo/s;'<br /> BM> 1<br /> <br /> BM> $ <br /> <br /> BM> However, this is clearly a silly edge case, as the whole point of /sm is<br /> BM> to remove the need to ever set $*.<br /> <br /> from perlvar:<br /> <br /> $* Set to a non-zero integer value to do multi-line matching<br /> within a string, 0 (or undefined) to tell Perl that it can<br /> assume that strings contain a single line, for the purpose of<br /> optimizing pattern matches. Pattern matches on strings con¡¾<br /> taining multiple newlines can produce confusing results when $*<br /> is 0 or undefined. Default is undefined. (Mnemonic: * matches<br /> multiple things.) This variable influences the interpretation<br /> of only "^" and "$". A literal newline can be searched for even<br /> when "$* == 0".<br /> <br /> Use of $* is deprecated in modern Perl, supplanted by the "/s"<br /> and "/m" modifiers on pattern matching.<br /> <br /> Assigning a non-numerical value to $* triggers a warning (and<br /> makes $* act if "$* == 0"), while assigning a numerical value<br /> to $* makes that an implicit "int" is applied on the value.<br /> <br /> and the docs there are very muddy. they don't define 'multiline<br /> matching' and they claim confusing results when $* is disabled. i don't<br /> find the results confusing :)<br /> <br /> uri<br /> <br /> -- <br /> Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com<br /> --Perl Consulting, Stem Development, Systems Architecture, Design and Coding-<br /> Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 04.09.2007 04:32:12 von Petr Vileta</span> <p>Tad McClellan wrote:<br /> > Petr Vileta <stoupa@practisoft.cz> wrote:<br /> >> Dr.Ruud wrote:<br /> >>> Petr Vileta schreef:<br /> ><br /> ><br /> >>>> $t =~s/^\s*|\s*$//sg;<br /> ><br /> >>> The /s modifier should not be there.<br /> ><br /> >> but /s modifier I must use<br /> ><br /> ><br /> > If you think so, then you do not yet understand what /s does.<br /> ><br /> > It makes dot match a newline.<br /> ><br /> > It therefore has no effect at all when your pattern does not contain<br /> > a dot.<br /> ><br /> > Your pattern does not contain a dot, so the /s modifier should not be<br /> > there.<br /> I must say - you are right. I had read O'Reilly "Programming in Perl" but I <br /> not found the clean explanation of /s modifier. The book say only "/s tell <br /> to Perl to use multi-line string as single-line". But nowhere is explained <br /> what is the multi-line string. I assume that this is the string where is one <br /> or more "\n".<br /> But for my practical live I assume that is better to use /s needlesly then <br /> omit to use /s for damned string containing "\n" :-)<br /> -- <br /> <br /> Petr Vileta, Czech republic<br /> (My server rejects all messages from Yahoo and Hotmail. Send me your mail <br /> from another non-spammer site please.)</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 04.09.2007 06:08:36 von Peter Makholm</span> <p>Ben Morrow <ben@morrow.me.uk> writes:<br /> <br /> >> PM> The /s-modifier withou the /m-modifier also forces ^ and $ to mean<br /> >> PM> beginning and end of string no matter what $* is. But you shouldn't<br /> >> PM> use $* so for every sane piece of code you're right.<br /> >> <br /> >> /s and /m are independent so i wouldn't use the word 'forces'. the<br /> >> behavior of ^ and $ are not affected by /s.<br /> <br /> Quite surprised? It took me many reading of the documentation to<br /> understand it too, ...<br /> <br /> > No, bizarrely enough Peter seems to be correct, in that iff $* is set /s<br /> > affects ^ and $ as well, undoing the effects of setting $*:<br /> <br /> .... but it works just as documented in perlre:<br /> <br /> The "/s" and "/m" modifiers both override the $* setting. That is,<br /> no matter what $* contains, "/s" without "/m" will force "^" to<br /> match only at the beginning of the string and "$" to match only at<br /> the end (or just before a newline at the end) of the string.<br /> Together, as /ms, they let the "." match any character whatsoever,<br /> while still allowing "^" and "$" to match, respectively, just after<br /> and just before newlines within the string.<br /> <br /> That is, concerning '$' and '^', the /s modifier works as if $* is<br /> false, the /m modifier works as if $* is true, and both modifiers<br /> works as if $* is true.<br /> <br /> But again, nobody should change $*, so the simple explanations will do<br /> for all modern code. <br /> <br /> //Makholm</p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 04.09.2007 07:14:50 von 1usa</span> <p>"Petr Vileta" <stoupa@practisoft.cz> wrote in<br /> news:fbh13i$1upj$2@ns.felk.cvut.cz: <br /> <br /> > Anno Siegel wrote:<br /> >> On 2007-09-03 03:17:24 +0200, Uri Guttman <uri@stemsystems.com> said:<br /> >><br /> >>> like michele said, this is too trivial to need a sub or a library.<br /> >><br /> >> That too.<br /> >><br /> > As the case may be ;-) When you remove blanks 50 times in 50kb source<br /> > code then is better to use sub or library.<br /> <br /> That is some bad code you write then.<br /> <br /> Referring back to your example about normalizing parameter values <br /> obtained from a CGI form, you could do all the required normalization in <br /> one and only place in the code. In fact, you could trim all the CGI <br /> parameters passed in a few lines:<br /> <br /> <br /> my $cgi = CGI->new<br /> my @form_params = $cgi->param;<br /> <br /> for my $p ( @form_params ) {<br /> for my $v ( $cgi->param( $p ) ) {<br /> next unless defined $v;<br /> $v =~ s/^\s+//;<br /> $v =~ s/\s+$//;<br /> }<br /> }<br /> <br /> How can it be that you need to do this in fifty different places? Did <br /> you know about lists and loops?<br /> <br /> Sinan<br /> <br /> -- <br /> A. Sinan Unur <1usa@llenroc.ude.invalid><br /> (remove .invalid and reverse each component for email address)<br /> clpmisc guidelines: <URL:http://www.augustmail.com/~tadmc/clpmisc.shtml></p> </article> <article> <h2>Re: FAQ 4.32 How do I strip blank space from the beginning/end of a string?</h2><span>am 08.09.2007 06:37:13 von sln</span> <p>On Tue, 04 Sep 2007 05:14:50 GMT, "A. Sinan Unur" <1usa@llenroc.ude.invalid> wrote:<br /> <br /> >"Petr Vileta" <stoupa@practisoft.cz> wrote in<br /> >news:fbh13i$1upj$2@ns.felk.cvut.cz: <br /> ><br /> >> Anno Siegel wrote:<br /> >>> On 2007-09-03 03:17:24 +0200, Uri Guttman <uri@stemsystems.com> said:<br /> >>><br /> >>>> like michele said, this is too trivial to need a sub or a library.<br /> >>><br /> >>> That too.<br /> >>><br /> >> As the case may be ;-) When you remove blanks 50 times in 50kb source<br /> >> code then is better to use sub or library.<br /> ><br /> >That is some bad code you write then.<br /> ><br /> >Referring back to your example about normalizing parameter values <br /> >obtained from a CGI form, you could do all the required normalization in <br /> >one and only place in the code. In fact, you could trim all the CGI <br /> >parameters passed in a few lines:<br /> ><br /> ><br /> >my $cgi = CGI->new<br /> >my @form_params = $cgi->param;<br /> ><br /> >for my $p ( @form_params ) {<br /> > for my $v ( $cgi->param( $p ) ) {<br /> > next unless defined $v;<br /> > $v =~ s/^\s+//;<br /> > $v =~ s/\s+$//;<br /> > }<br /> >}<br /> ><br /> >How can it be that you need to do this in fifty different places? Did <br /> >you know about lists and loops?<br /> ><br /> >Sinan<br /> <br /> Maybe you should try writing more than 1 liners and stop<br /> 'Pontificating'</p> </article> <footer> <a href="/">Index</a> | <a href="/impressum.php">Impressum</a> | <a href="/datenschutz.php">Datenschutz</a> | <a href="https://www.xodox.de/">XODOX</a> </footer> </main> </body> </html>