{"id":5441,"date":"2024-05-26T03:00:00","date_gmt":"2024-05-26T07:00:00","guid":{"rendered":"https:\/\/www.both.org\/?p=5441"},"modified":"2024-05-22T10:27:26","modified_gmt":"2024-05-22T14:27:26","slug":"use-grep-to-solve-a-2-dimensional-word-puzzle","status":"publish","type":"post","link":"https:\/\/www.both.org\/?p=5441","title":{"rendered":"Use \u2018grep\u2019 to solve a 2-dimensional word puzzle"},"content":{"rendered":"
\r\n
\r\n \r\n <\/i>\r\n <\/a>\r\n <\/span>\r\n<\/div><\/div>\n

As a systems administrator, you need to keep a lot of \u201ctools\u201d on your \u201ctool belt\u201d of skills. Understanding how to best apply different tools and concepts to new problems can turn a difficult problem into a small one. One skill I used frequently when I worked as a systems administrator – early in my career – was regular expressions<\/em>.<\/p>\n\n\n\n

You can learn more about regular expressions from the regex<\/code> manual page, in section 7 of the online manual, with man 7 regex<\/code>. The basics of regular expressions are:<\/p>\n\n\n\n

Character<\/th>Meaning<\/th><\/tr><\/thead>
^<\/code><\/td>The start of a line<\/td><\/tr>
$<\/code><\/td>The end of a line<\/td><\/tr>
.<\/code><\/td>Any single character<\/td><\/tr>
[<\/code> and ]<\/code><\/td>Match any of a set of characters, such as [ab]<\/code> to match either<\/em> a<\/code> or b<\/code>, or [a-z]<\/code> to match any<\/em> lowercase letter<\/td><\/tr>
*<\/code><\/td>Zero or more of the thing before it, like a*<\/code> to match zero or more of a<\/code><\/td><\/tr>
?<\/code><\/td>Zero or one of the thing, like a?<\/code> to match an a<\/code> that may or may not be there<\/td><\/tr>
+<\/code><\/td>One or more of the thing, like a+<\/code> to match one or more of a<\/code><\/td><\/tr><\/tbody><\/table>
Regular expression characters and what they mean<\/figcaption><\/figure>\n\n\n\n

Playing a word puzzle game<\/h2>\n\n\n\n

I like to play puzzle games to relax, especially word puzzles. I wrote before about playing the Wordle game<\/a>, but recently I discovered another game: Keyword<\/a> is a word puzzle game that presents six words of different lengths, written vertically, each missing a single letter. The missing letters also form a word that runs horizontally. You need to pick the right letters to both fill in the missing letters from the words<\/em> and create a new six-letter word<\/em>.<\/p>\n\n\n\n

This is an excellent opportunity to practice using grep<\/code> to leverage regular expressions to find words in the system dictionary that match the six words – and at the same time, uncover the hidden word.<\/p>\n\n\n\n

<\/figure>\n\n\n\n

In this puzzle, we have six words, each missing one letter:<\/p>\n\n\n\n

    \n
  1. at?lete<\/li>\n\n\n\n
  2. d?al<\/li>\n\n\n\n
  3. dec?de<\/li>\n\n\n\n
  4. p?ot<\/li>\n\n\n\n
  5. ?ear<\/li>\n\n\n\n
  6. parc?ment<\/li>\n<\/ol>\n\n\n\n

    Some of these may be immediately obvious. I can\u2019t imagine the first word as being anything other than athlete<\/strong>. The last word seems obvious as parchment<\/strong>. But the third word could be either decide<\/strong> or decade<\/strong>.<\/p>\n\n\n\n

    List the possible words<\/h2>\n\n\n\n

    Let\u2019s use grep<\/code> to match each of the possible six words from a dictionary of possible words. On Linux, the \/usr\/share\/dict\/words<\/code> file contains a list of over a half-million correctly-spelled words, such as you might use in a spell-checking application. Let\u2019s use regular expressions to match each incomplete word to valid words from the words<\/code> file. To match each word, we only need a few regular expression characters: ^<\/code> and $<\/code> and [a-z]<\/code>.<\/p>\n\n\n\n

    $ grep '^at[a-z]lete$' \/usr\/share\/dict\/words\nathlete\n\n$ grep '^d[a-z]al$' \/usr\/share\/dict\/words\ndeal\ndhal\ndial\ndual\n\n$ grep '^dec[a-z]de$' \/usr\/share\/dict\/words\ndecade\ndecede\ndecide\ndecode\n\n$ grep '^p[a-z]ot$' \/usr\/share\/dict\/words\nphot\nplot\npoot\n\n$ grep '^[a-z]ear$' \/usr\/share\/dict\/words\nbear\ndear\nfear\ngear\nhear\njear\nlear\nmear\nnear\npear\nrear\nsear\ntear\nwear\nyear\n\n$ grep '^parc[a-z]ment$' \/usr\/share\/dict\/words\nparchment<\/code><\/pre>\n\n\n\n
    Some of the incomplete words have only one match in the words<\/code> file, while others have quite a few. Still, matching these words with grep<\/code> gives us a lot of information to fill in the missing word. The matched words from the dictionary tell us what letters can appear in each position:<\/p>\n\n\n\n
      \n
    1. The first letter can only be h<\/strong><\/li>\n\n\n\n
    2. The second letter can be e<\/strong>, h<\/strong>, i<\/strong>, or u<\/strong><\/li>\n\n\n\n
    3. The third letter might be a<\/strong>, e<\/strong>, i<\/strong>, or o<\/strong><\/li>\n\n\n\n
    4. The fourth letter is one of h<\/strong>, l<\/strong>, or o<\/strong><\/li>\n\n\n\n
    5. The fifth letter has several possibilities!<\/li>\n\n\n\n
    6. The last letter can only be h<\/strong><\/li>\n<\/ol>\n\n\n\n
      Narrowing the options<\/h2>\n\n\n\n
      We can build a regular expression to match a six-letter word from the dictionary, where each letter is what we have uncovered. For each letter, we\u2019ll use a pattern to match a specific letter, like [ehiu]<\/code> to match one of e<\/strong>, h<\/strong>, i<\/strong>, or u<\/strong>. I\u2019m not sure I want to type in all fifteen possible letters for the fifth letter, so let\u2019s see how far we can get by specifying .<\/code> for that letter, to match any character at that position.<\/p>\n\n\n\n
      Our grep<\/code> command to find the possible letters looks like this:<\/p>\n\n\n\n
      $ grep '^h[ehiu][aeio][hlo].h$' \/usr\/share\/dict\/words\nhealth<\/code><\/pre>\n\n\n\n
      So now we have discovered exactly one<\/em> six-letter word that also fills in the missing letter for each incomplete word: health<\/strong>. And that\u2019s correct!<\/p>\n\n\n\n
      \"screenshot<\/figure>\n\n\n\n
      Matching patterns<\/h2>\n\n\n\n
      Regular expressions match patterns in text. Here, we\u2019ve used grep<\/code> and regular expressions in a fun way to play a word puzzle game. With a well-formed regular expression, you can also find specific messages in a log file, or uncover errors in output files. Practice using regular expressions so you can add this great \u201ctool\u201d to your virtual \u201ctool belt\u201d of system administrator skills.<\/p>\n","protected":false},"excerpt":{"rendered":"
      Regular expressions match patterns and help you solve problems.<\/p>\n","protected":false},"author":33,"featured_media":2820,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","footnotes":""},"categories":[100,69,83],"tags":[104,147,383],"class_list":["post-5441","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-command-line","category-fun","category-problem-solving","tag-command-line","tag-fun","tag-regular-expressions"],"modified_by":"Jim Hall","_links":{"self":[{"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/5441","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/users\/33"}],"replies":[{"embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5441"}],"version-history":[{"count":1,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/5441\/revisions"}],"predecessor-version":[{"id":5445,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/posts\/5441\/revisions\/5445"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=\/wp\/v2\/media\/2820"}],"wp:attachment":[{"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5441"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5441"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.both.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5441"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}