Substitution problem.

Leitchn has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Substitution problem. by Dominus (Parson) on Nov 25, 2000 at 05:48 UTC
You think you're using `quotemeta`, but you aren't. Instead, you are telling Perl to look for a string that begins with a `q` followed by a `u` and soforth. Perl does not evaluate arbitrary expressions on the left side of `s///`. Try this: `for $count (0..52) { my $pattern = quotemeta($array1{$count}); $sometext =~ s/$pattern/$array2{$count}/g; }` [download] Or (does the same thing): `for $count (0..52) { $sometext =~ s/\Q$array1{$count}/$array2{$count}/g; }` [download] Notice also: No `'` single quotes around variable names, because single quotes prevent variables from being interpolated. Also no `quotemeta` on the right side, because it is not necessary.	[reply] [d/l] [select]
Re: Substitution problem. by snax (Hermit) on Nov 25, 2000 at 20:13 UTC
Why don't you try to do this more "all at once"? First, note that `tr///` is the right tool for single character substitution lists -- it's heavily optimized for this kind of thing. Second, it seems to me that your `$count` variable may be redundant. Why not make one hash with keys the "old" values and the values the "new" values -- that sounds odd, but basically: `$replacements{quotemeta($array1{$count})} = $array2{$count};` [download] ...but do this where you are building `%array1` and `%array2` so you don't need to use `$count` or the array hashes at all. Aside: in perl's common parlance, "array" typically refers to an integer indexed object like you are using your hashes above, but the hash construct is much more flexible (and more expensive to use in terms of resources). Anyway, with a `%replacements` hash you can then do: `my $repl_str = join( '\|', keys %replacements); $someText =~ s/($replstr)/%replacements{$1}/g;` [download] This does all your replacements with one evaluation. Again, note that this is really only appropriate when you need to replace more than single characters.	[reply] [d/l] [select]
Re: Substitution problem. by Fastolfe (Vicar) on Nov 25, 2000 at 05:45 UTC
First of all, you're only using the `/g` flag, which will interpret your expressions literally and do interpolation. So you end up with this: `s/quotemeta('[')/quotemeta('x')/g;` [download] Which presumably (if it were valid) would match the text "quotemeta'`[`'", putting '`[`' into $1. Try doing this: `s/\Q$array1{$count}\E/$array2{$count}/g;` [download] Or, if each array element simply has one character apiece (as you suggest), forego the loop entirely and use tr: `$from = join('', @array1); # or set up $from and $to $to = join('', @array2); # to begin with tr/$from/$to/; # e.g. "abc" =~ tr/ab/xy/ ==> "xyc"` [download]	[reply] [d/l] [select]
Re: Substitution problem. by Dominus (Parson) on Nov 25, 2000 at 08:47 UTC
Says fastolfe: > `tr/$from/$to/;` This won't work, because variables are not interpolated inside of `tr///`. Your line replaces `$` with `$`; `f` with `t`; and `r`, `o`, and `m` with `o`.	[reply]
Re: Re: Substitution problem. by snax (Hermit) on Nov 25, 2000 at 19:50 UTC
Indeed, so that one would want to use: `eval("tr/$from/$to/");` [download] More and more the only place I end up using eval is in this type of construction.	[reply] [d/l]
Re (tilly) 3: Substitution problem. by tilly (Archbishop) on Nov 25, 2000 at 20:08 UTC
Re: Re (tilly) 3: Substitution problem. by snax (Hermit) on Nov 25, 2000 at 20:15 UTC


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