Solutions to Exercises

Solution 3.1

Question

One solution to this problem is to :mark (here with named mark “a”) each mid-file occurrence of ^CHAPTER before we copy it to the end of the file. We can then use the marked line address 'a with the :substitute command to change the mid-file occurrence to lower case:

   global /^CHAPTER/ mark a | copy $ | 'a substitute /HAPTER/hapter/

Solution 3.2

Question

Using a line range that yields 16 lines in a :global command runs its :substitution command 16 times, even when the range of the :substitution command is fixed to one line (217). Each time it inserts a single backslash. (The double backslash in the replacement pattern is necessary because the backslash is a special character even there.)

  1 , 16 global /^/ 217 substitute /n(PDu/\\&/
Note

The & character used in the replacement pattern expands to the entire match found by the search pattern.

Also, this solution suffers from the necessity that there be at least 16 lines in the file.

Solution 3.3

Question

The paragraphs can be numbered with just two global commands. The first one:

  global /^\.pp/ . , $ substitute //&I/

goes to each line beginning with a start-of-paragraph macro, then runs a substitute command from that line through the end of the file that puts a capital letter I after each such macro. So the substitute command that runs from the first marked line puts an I after every one of the macros; from the second marked line it puts an I after every such macro except the first; from the third marked line it puts an I after every such macro except the first and the second; and so on. Thus, after this global finishes, you have a string of the letter I after every macro that is equal in number to the paragraph’s number. That is, after the macro for the third paragraph you have the string "III"; after paragraph 5 you have the string "IIIII"; etcetera. Already you have Roman numerals (of a very primitive sort) numbering the paragraphs. A second global command puts those Roman numerals into canonical form:

  global /^\.pp/ substitute /IIIII/V/g | substitute /VV/X/g | substitute /IIII/IV/
Note As you’ll learn in the next installment of this tutorial, a lower-case letter g at the end of a substitute command tells the editor to perform the substitution as many times as it can on each line.

To see how our second global command sets things right, consider the case of the 19th paragraph. The next four lines show what the macro line looks like at the start of the command and how it has changed after each of the three substitute commands has done its work:

.ppIIIIIIIIIIIIIIIIIII
.ppVVVIIII
.ppXVIIII
.ppXVIV
Note Astute readers will realize that the paragraphs could have been numbered with just one global command. Each macro line has all the capital I letters it will get before global leaves it for the next line. So we could have had the command string start by marking the line, next run the substitution that adds a capital I to all remaining macro lines, then return to the line and run the substitutions that produce a true Roman numeral. Bonus points for actually trying this.