Here's a sample program to show the problems I'm having with regexps:
my $s = "a\tb";
my $m1 = "\t";
my $m2 = "\\t"; # both "\t" and "\\t" are treated specially
my $r1 = "\t";
my $r2 = "\\t";
my $s1 = $s;
my $s2 = $s;
$s1 =~ s/$m1/$r1/;
$s2 =~ s/$m1/$r2/;
print "\"$s\" =~ s/$m1/$r1/ -> \"$s1\"\n";
print "\"$s\" =~ s/$m1/$r2/ -> \"$s2\"\n";
my $s1 = $s;
my $s2 = $s;
$s1 =~ s/$m2/$r1/;
$s2 =~ s/$m2/$r2/;
print "\"$s\" =~ s/$m2/$r1/ -> \"$s1\"\n";
print "\"$s\" =~ s/$m2/$r2/ -> \"$s2\"\n";
$s = "aabcc";
$s1 = $s;
$s2 = $s;
my $m = "a(b)c"; # "(" is is treated specially, but "\\(" isn't
my $r = "$1";
$s1 =~ s/$m/$r/; # $r (= "$1") is substituted with an empty string
$s2 =~ s/$m/$1/; # $1 is substituted with "b"
print "\"$s\" =~ s/$m/\$r/ -> \"$s1\", where \$r=\"\$1\"\n";
print "\"$s\" =~ s/$m/\$1/ -> \"$s2\"\n";
It prints:
"a b" =~ s/ / / -> "a b"
"a b" =~ s/ /\t/ -> "a\tb"
"a b" =~ s/\t/ / -> "a b"
"a b" =~ s/\t/\t/ -> "a\tb"
"aabcc" =~ s/a(b)c/$r/ -> "ac", where $r="$1"
"aabcc" =~ s/a(b)c/$1/ -> "abc"
The first problem (as you've probably already realized from the first
4 lines of the output) is that in the search expression both the tab
character "\t" and the backslash+t sequence "\\t" are treated the
same, as the tab character. Why is that?
The second problem is that in the replace expression the same backslash
+t sequence isn't treated "\\t" the same way as in the search
expression. Why is this inconsistency? Can I somehow force s/// to
treat "\\t" in replace as "\t"?
The third problem should be apparent from the last 2 lines of the
output. I want the $1 match (and possibly a few more) to come from
elsewhere (string data) and not be predetermined by the code. But it
doesn't seem to work this way. Is it possible to fix this?
Thanks,
Alex
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