Re^6: Anagrams & Letter Banks

Although they are similar, Unix shell (sh, csh, tcsh, bash, etc.) grep and Perl grep are not exactly the same.

In Perl, grep takes a list or array of values as input, and outputs those for which the grep command returns true.

Comment on Re^6: Anagrams & Letter Banks

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Re^7: Anagrams & Letter Banks by dominick_t (Acolyte) on Oct 27, 2017 at 21:55 UTC
Thank you, Laurent_R. If it is the case that grep outputs the values themselves that are true, how is it that the `next unless grep !/(.).\1/, @list;`line appears to be doing what I want it to in this: `for (sort keys %words) { my @list = sort @{$words{$_}}; next unless @list > 1; next unless grep !/(.).\1/, @list; print "@list\n";` [download] If grep outputs the words themselves, why is the "next unless" part working?	[reply] [d/l] [select]
Re^8: Anagrams & Letter Banks by Cristoforo (Curate) on Oct 27, 2017 at 22:23 UTC
If grep outputs the words themselves, why is the "next unless" part working? In list context, grep will output the words, but in scalar context, (here forced by 'unless'), grep will return the number (0 1 2 ...) of times the condition it is testing is true. In this code, if grep tests a word composed of unique letters, the regex test will fail and applying the negation (!), forms a double negative which is equal to true. Here grep returns 1, (or 2 or more depending how many words are made up of unique letters in `@list`).	[reply] [d/l]