On May 14, Noah Sussman said:
>I am trying to write a simple script to insert ALT attributes into IMG tags
>that don't have them, leaving other IMG tags untouched.
>
>The problem is that I can't figure out how to tell Perl to search for
>strings beginning with "<IMG", ending with ">" AND not containing "ALT="
>(and it has to do this over multiple lines as well!).
First, you need to construct a proper IMG-tag-matching regex.
my $value = qr{
" [^"]* " | # a double-quoted value
' [^']* ' | # a single-quoted value
[^\s>]* # an unquoted value
}x;
my $attr = qr{
\s* # 0 or more whitespace
\w+ # the attribute
(?:
\s* # 0 or more whitespace
= # an '='
\s* # 0 or more whitespace
$value # its value
)? # but that part's optional
}x;
my $tag = qr{
<img # the start of the tag
(?:
\s+ # 1 or more whitespace
$attr* # 0 or more attributes
)? # but that part's optional
\s* # 0 or more whitespace
> # the end of the tag
}ix;
Now you can match the <img> tags:
$HTML =~ s/($tag)/.../g;
However, you only want to match tags without ALT attributes, so...
my $attr = qr{
\s* # 0 or more whitespace
(?!alt) # as long as we're not about to match "alt"...
\w+ # the attribute
(?:
\s* # 0 or more whitespace
= # an '='
\s* # 0 or more whitespace
$value # its value
)? # but that part's optional
}xi;
Now you can do:
$HTML =~ s/($tag)/add_alt($1)/eg;
sub add_alt {
my $tag = shift;
substr($tag, -1, 0, ' alt="FOO!"'); # insert alt attr.
return $tag;
}
--
Jeff "japhy" Pinyan [EMAIL PROTECTED] http://www.pobox.com/~japhy/
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Perl Programmer at RiskMetrics Group, Inc. http://www.riskmetrics.com/
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