sed is a very powerful tool. A simple sed statement may turn a cat into cement. Observe: echo cat | sed statement I was asked by mariom@ircnet whether is it possible to implement the Euklidean algorithm (the one that computes the greatest common divisor) in awk. awk is a Turing complete language, so the answer is yes, it is possible. There is a snippet proposed by mariom:<\/p>\n
{\r\n a = $1;\r\n b = $2;\r\n while (b != 0) {\r\n c = a % b;\r\n a = b;\r\n b = c;\r\n }\r\n print a\r\n}<\/pre>\nAnyway, my response was that it is possible even in sed. Is it? Of course! Sed is a Turing complete language. Though I had no idea how to write it in sed. I use sed for simple substitutions only, but I could not admit that! I started googling for arithmetic operations in sed and I found<\/p>\n
a dc implementation in pure sed<\/a>. So the next question is how to implement the Euklidean algorithm in dc. It turned out to be quite simple, see:<\/p>\n[lalb%sclbsalcsblb0<\/pre>\nThis code assumes that there are two integers on the stack. So you can test it with something like that:<\/p>\n
echo '20 25 [lalb%sclbsalcsblb0<\/pre>\nLet’s analyze what is happening there. There is F macro that is equivalent of “while” loop in awk code. It<\/p>\n
l<\/strong>oads the values of a<\/strong> and b<\/strong> registers on the stack. Then replaces them with their reminder and s<\/strong>aves it in the c<\/strong> registers.<\/p>\nlbsalcsb<\/pre>\nstatement just copies the value of<\/p>\n
b<\/strong> to a<\/strong> and c<\/strong> to b<\/strong>. Finaly it compares the value of b<\/strong> with 0<\/strong>. If former is greater it executes F<\/strong> (note: recurrence. It is the only way to implement a loop in dc). Otherwise it quits.<\/p>\nsasblFxlap<\/pre>\nstatement is an entry point. It saves values from stack in the\u00a0<\/p>\n
a<\/strong> and b<\/strong> registers, then executes F<\/strong> and prints the content of the\u00a0a<\/strong> register. So this sed script is an equivalent of awk script that executes Euklidean algothm. Now it is enough to embed the dc script into dc.sed, et voila! Enjoy: Euclidean algorithm implemented in pure sed.<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"sed is a very powerful tool. A simple sed statement may turn a cat into cement. Observe: echo…\n","protected":false},"author":10,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[692,537],"_links":{"self":[{"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/posts\/509"}],"collection":[{"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/users\/10"}],"replies":[{"embeddable":true,"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/comments?post=509"}],"version-history":[{"count":25,"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/posts\/509\/revisions"}],"predecessor-version":[{"id":15602,"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/posts\/509\/revisions\/15602"}],"wp:attachment":[{"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/media?parent=509"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/categories?post=509"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/touk.pl\/blog\/wp-json\/wp\/v2\/tags?post=509"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}