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12.2 Generating a Formatted Index

The process of generating an index usually involves three steps:

  • Code the index entries in the document.

  • Format the document, producing index entries with page numbers.

  • Process the index entries to sort them, combining entries that differ only in page number, and then preparing the formatted index.

This process remains pretty much the same whether using troff , other coded batch formatters, or a WYSIWYG formatter such as FrameMaker , although the steps are not as clearly separated with the latter. However, I will be describing how we use troff to generate an index such as the one for this book. We code the index using the following macros:

Macro Description
.XX Produces general index entries.
.XN Creates "see" or "see also" cross references.
.XB Creates bold page entry indicating primary reference.
.XS Begins range of pages for entry.
.XE Ends range of pages for entry.

These macros take a single quoted argument, which can have one of several forms, indicating primary, secondary, or tertiary keys:

" primary [ : secondary [ ; tertiary ]]"

A colon is used as the separator between the primary and secondary keys. To support an earlier coding convention, the first comma is interpreted as the separator if no colon is used. A semicolon indicates the presence of a tertiary key. The page number is always associated with the last key.

Here is an entry with only a primary key:

.XX "XView"

The next two entries specify a secondary key:

.XX "XView: reserved names"
.XX "XView, packages"

The most complex entries contain tertiary keys:

.XX "XView: objects; list"
.XX "XView: objects; hierarchy of"

Finally, there are two types of cross references:

.XN "error recovery: (see error handling)" 
.XX "mh mailer: (see also xmh mailer)"

The "see" entry refers a person to another index entry. The "see also" is typically used when there are entries for, in this case, "mh mailer," but there is relevant information catalogued under another name. Only "see" entries do not have page numbers associated with them.

When the document is processed by troff , the following index entries are produced:

XView    42
XView: reserved names   43
XView, packages 43
XView: objects; list of 43
XView: objects; hierarchy of    44
XView, packages 45
error recovery: (See error handling) 
mh mailer: (see also xmh mailer)    46

These entries serve as input to the indexing program. Each entry (except for "see" entries) consists of the key and a page number. In other words, the entry is divided into two parts and the first part, the key, can also be divided into three parts. When these entries are processed by the indexing program and the output is formatted, the entries for "XView" are combined as follows:

XView, 42
	objects; hierarchy of, 44; 
	   list of, 43
	packages, 43,45
	reserved names, 43

To accomplish this, the indexing program must:

  • Sort the index by key and page number.

  • Merge entries that differ only in the page number.

  • Merge entries that have the same primary and/or secondary keys.

  • Look for consecutive page numbers and combine as a range.

  • Prepare the index in a format for display on screen or for printing.

This is what the index program does if you are processing the index entries for a single book. It also allows you to create a master index, an overall index for a set of volumes. To do that, an awk script appends either a roman numeral or an abbreviation after the page number. Each file then contains the entries for a particular book and those entries are uniquely identified. If we chose to use roman numerals to identify the volume, then the above entries would be changed to:

XView	42:I
XView: reserved names   43:I
XView: objects; list of 43:I

With multivolume entries, the final index that is generated might look like this:

XView, I:42; II:55,69,75
	objects; hierarchy of, I:44; 
          list of, I:43; II: 56 
	packages, I:43,45
	reserved names, I:43

For now, it's only important to recognize that the index entry used as input to the awk program can have a page number or a page number followed by a volume identifier.

12.2.1 The masterindex Program

Because of the length and complexity of this indexing application,[2] our description presents the larger structure of the program. Use the comments in the program itself to understand what is happening in the program line by line.

[2] The origins of this indexing program are traced back to a copy of an indexing program written in awk by Steve Talbott. I learned this program by taking it apart, and made some changes to it to support consecutive page numbering in addition to section-page numbering. That was the program I described in UNIX Text Processing . Knowing that program, I wrote an indexing program that could deal with index entries produced by Microsoft Word and generate an index using section-page numbering. Later, we needed a master index for several books in our X Window System Series. I took it as an opportunity to rethink our indexing program, and rewrite it using nawk, so that it supports both single-book and multiple-book indices. The AWK Programming Language contains an example of an index program that is smaller than the one shown here and might be a place to start if you find this one too complicated. It does not, however, deal with keys. That indexing program is a simplified version of the one described in Bell Labs Computing Science Technical Report 128, Tools for Printing Indexes , October 1986, by Brian Kernighan and Jon Bentley. [D.D.]

After descriptions of each of the program modules, a final section discusses a few remaining details. For the most part, these are code fragments that deal with nitty-gritty, input-related problems that had to be solved along the way. The shell script masterindex [3] allows the user to specify a number of different command-line options to specify what kind of index to make and it invokes the necessary awk programs to do the job. The operations of the masterindex program can be broken into five separate programs or modules that form a single pipe.

[3] This shell script and the documentation for the program are presented in Appendix C . You might want to first read the documentation for a basic understanding of using the program.

input.idx | sort | pagenums.idx | combine.idx | format.idx

All but one of the programs are written using awk. For sorting the entries, we rely upon sort , a standard UNIX utility. Here's a brief summary of what each of these programs does:

input.idx

Standardizes the format of entries and rotates them.

sort

Sorts entries by key, volume, and page number.

pagenums.idx

Merges entries with same key, creating a list of page numbers.

combine.idx

Combines consecutive page numbers into a range.

format.idx

Prepares the formatted index for the screen or processing by troff .

We will discuss each of these steps in a separate section.

12.2.2 Standardizing Input

This input.idx script looks for different types of entries and standardizes them for easier processing by subsequent programs. Additionally, it automatically rotates index entries containing a tilde (~). (See the section "Rotating Two Parts" later in this chapter.)

The input to the input.idx program consists of two tab-separated fields, as described earlier. The program produces output records with three colon-separated fields. The first field contains the primary key; the second field contains the secondary and tertiary keys, if defined; and the third field contains the page number.

Here's the code for input.idx program:

#!/work/bin/nawk -f
# ------------------------------------------------
# input.idx -- standardize input before sorting
# Author:  Dale Dougherty
# Version 1.1   7/10/90
# 
# input is "entry" tab "page_number"
# ------------------------------------------------
BEGIN { FS = "\t"; OFS = "" }

#1 Match entries that need rotating that contain a single tilde
   # $1 ~ /~[^~]/  # regexp does not work and I do not know why 
$1 ~ /~/ && $1 !~ /~~/ { 
   # split first field into array named subfield 
	n = split($1, subfield, "~")
	if (n == 2) {
	# print entry without "~" and then rotated
		printf("%s %s::%s\n", subfield[1], subfield[2], $2)
		printf("%s:%s:%s\n", subfield[2], subfield[1], $2)
	}
	next
}# End of 1

#2 Match entries that contain two tildes 
$1 ~ /~~/ { 
   # replace ~~ with ~	
	gsub(/~~/, "~", $1)
} # End of 2

#3  Match entries that use "::" for literal ":". 
$1 ~ /::/ { 
   # substitute octal value for "::"
	gsub(/::/, "\\72", $1) 
}# End of 3

#4 Clean up entries 
{
   # look for second colon, which might be used instead of ";"
	if (sub(/:.*:/, "&;", $1)) {
		sub(/:;/, ";", $1)	
	}
   # remove blank space if any after colon.
	sub(/: */, ":", $1)
   # if comma is used as delimiter, convert to colon. 
	if ( $1 !~ /:/ ) {
	# On see also & see, try to put delimiter before "(" 
		if ($1 ~ /\([sS]ee/) {
			if (sub(/, *.*\(/, ":&", $1)) 
				sub(/:, */, ":", $1)
			else
				sub(/  *\(/, ":(", $1)
		}
		else { # otherwise, just look for comma
			sub(/, */, ":", $1)
		}
	}
	else {
		# added to insert semicolon in "See"
		if ($1 ~ /:[^;]+ *\([sS]ee/) 
			sub(/  *\(/, ";(", $1)
	}	
}# End of 4

#5 match See Alsos and fix for sort at end
$1 ~ / *\([Ss]ee +[Aa]lso/ { 
  # add "~zz" for sort at end
	sub(/\([Ss]ee +[Aa]lso/, "~zz(see also", $1) 
	if ($1 ~ /:[^; ]+ *~zz/) {
		sub(/ *~zz/, "; ~zz", $1)
	}
  # if no page number
	if ($2 == "") {
		print $0 ":" 
		next
	}
	else {
	# output two entries: 
	# print See Also entry w/out page number
		print $1 ":"
	# remove See Also 
		sub(/ *~zz\(see also.*$/, "", $1) 
		sub(/;/, "", $1)
	# print as normal entry
		if ( $1 ~ /:/ )
			print $1 ":" $2
		else
			print $1 "::" $2
		next
	}
}# End of 5

#6 Process entries without page number (See entries)
(NF == 1 || $2 == "" || $1 ~ /\([sS]ee/) { 
   # if a "See" entry
	if ( $1 ~ /\([sS]ee/ ) { 
		if ( $1 ~ /:/ ) 
			print $1 ":"
		else  
			print $1 ":"
		next
	}
	else  { # if not a See entry, generate error
		printerr("No page number")
		next
        }
}# End of 6

#7 If the colon is used as the delimiter 
$1 ~ /:/ { 
   # output entry:page
	print $1 ":" $2
	next
}# End of 7

#8  Match entries with only primary keys.
{
	print $1 "::" $2
}# End of 8

# supporting functions
# 
# printerr -- print error message and current record
#		Arg: message to be displayed

function printerr (message) {
	# print message, record number and record
	printf("ERROR:%s (%d) %s\n", message, NR, $0) > "/dev/tty"
}

This script consists of a number of pattern-matching rules to recognize different types of input. Note that an entry could match more than one rule unless the action associated with a rule calls the next statement.

As we describe this script, we will be referring to the rules by number. Rule 1 rotates entries containing a tilde and produces two output records. The split() function creates an array named subfield that contains the two parts of the compound entry. The two parts are printed in their original order and are then swapped to create a second output record in which the secondary key becomes a primary key.

Because we are using the tilde as a special character, we must provide some way of actually entering a tilde. We have implemented the convention that two consecutive tildes are translated into a single tilde. Rule 2 deals with that case, but notice that the pattern for rule 1 makes sure that the first tilde it matches is not followed by another tilde.[4]

[4] In the first edition, Dale wrote, "For extra credit, please send me mail if you can figure out why the commented regular expression just before rule 1 does not do the job. I used the compound expression as a last resort." I'm ashamed to admit that this stumped me also. When Henry Spencer turned on the light, it was blinding: "The reason why the commented regexp doesn't work is that it doesn't do what the author thought. :-) It looks for tilde followed by a non-tilde character... but the second tilde of a ~~ combination is usually followed by a non-tilde! Using /[^~]~[^~]/ would probably work." I plugged this regular expression in to the program, and it worked just fine. [A.R.]

The order of rules 1 and 2 in the script is significant. We can't replace "~~" with "~" until after the procedure for rotating the entry.

Rule 3 does a job similar to that of rule 2; it allows "::" to be used to output a literal ":" in the index. However, since we use the colon as an input delimiter throughout the input to the program, we cannot allow it to appear in an entry as finally output until the very end. Thus, we replace the sequence "::" with the colon's ASCII value in octal. (The format.idx program will reverse the replacement.)

Beginning with rule 4, we attempt to recognize various ways of coding entries - giving the user more flexibility. However, to make writing the remaining programs easier, we must reduce this variety to a few basic forms.

In the "basic" syntax, the primary and secondary keys are separated by a colon. The secondary and tertiary keys are separated by a semicolon. Nonetheless the program also recognizes a second colon, in place of a semicolon, as the delimiter between the secondary and tertiary keys. It also recognizes that if no colon is specified as a delimiter, then a comma can be used as the delimiter between primary and secondary keys. (In part, this was done to be compatible with an earlier program that used the comma as the delimiter.) The sub() function looks for the first comma on the line and changes it to a colon. This rule also tries to standardize the syntax of "see" and "see also" entries. For entries that are colon-delimited, rule 4 removes spaces after the colon. All of the work is done using the sub() function.

Rule 5 deals with "see also" entries. We prepend the arbitrary string "~zz" to the "see also" entries so that they will sort at the end of the list of secondary keys. The pagenums.idx script, later in the pipeline, will remove "~zz" after the entries have been sorted.

Rule 6 matches entries that do not specify a page number. The only valid entry without a page number contains a "see" reference. This rule outputs "see" entries with ":" at the end to indicate an empty third field. All other entries generate an error message via the printerr() function. This function notifies the user that a particular entry does not have a page number and will not be included in the output. This is one method of standardizing input - throwing out what you can't interpret properly. However, it is critical to notify the user so that he or she can correct the entry.

Rule 7 outputs entries that contain the colon-delimiter. Its action uses next to avoid reaching rule 8.

Finally, rule 8 matches entries that contain only a primary key. In other words, there is no delimiter. We output "::" to indicate an empty second field.

Here's a portion of the contents of our test file. We'll be using it to generate examples in this section.

$ 

cat test


XView: programs; initialization 45
XV_INIT_ARGS~macro      46
Xv_object~type  49
Xv_singlecolor~type     80
graphics: (see also server image)
graphics, XView model   83
X Window System: events 84
graphics, CANVAS_X_PAINT_WINDOW 86
X Window System, X Window ID for paint window   87
toolkit (See X Window System).
graphics: (see also server image)
Xlib, repainting canvas 88
Xlib.h~header file      89

When we run this file through input.idx , it produces:

$ 

input.idx test


XView:programs; initialization:45
XV_INIT_ARGS macro::46
macro:XV_INIT_ARGS:46
Xv_object type::49
type:Xv_object:49
Xv_singlecolor type::80
type:Xv_singlecolor:80
graphics:~zz(see also server image):
graphics:XView model:83
X Window System:events:84
graphics:CANVAS_X_PAINT_WINDOW:86
X Window System:X Window ID for paint window:87
graphics:~zz(see also server image):
Xlib:repainting canvas:88
Xlib.h header file::89
header file:Xlib.h:89

Each entry now consists of three colon-separated fields. In the sample output, you can find examples of entries with only a primary key, those with primary and secondary keys, and those with primary, secondary, and tertiary keys. You can also find examples of rotated entries, duplicate entries, and "see also" entries.

The only difference in the output for multivolume entries is that each entry would have a fourth field that contains the volume identifier.

12.2.3 Sorting the Entries

Now the output produced by input.idx is ready to be sorted. The easiest way to sort the entries is to use the standard UNIX sort program rather than write a custom script. In addition to sorting the entries, we want to remove any duplicates and for this task we use the uniq program.

Here's the command line we use:

sort -bdf -t: +0 -1 +1 -2 +3 -4 +2n -3n | uniq

As you can see, we use a number of options with the sort command. The first option, -b , specifies that leading spaces be ignored. The -d option specifies a dictionary sort in which symbols and special characters are ignored. -f specifies that lower- and uppercase letters are to be folded together; in other words, they are to be treated as the same character for purposes of the sort. The next argument is perhaps the most important: -t: tells the program to use a colon as a field delimiter for sort keys. The " + " options that follow specify the number of fields to skip from the beginning of the line. Therefore, to specify the first field as the primary sort key, we use "+0." Similarly, the " - " options specify the end of a sort key. "-1" specifies that the primary sort key ends at the first field, or the beginning of the second field. The second sort field is the secondary key. The fourth field ("+3") if it exists, contains the volume number. The last key to sort is the page number; this requires a numeric sort (if we did not tell sort that this key consists of numbers, then the number 1 would be followed by 10, instead of 2). Notice that we sort page numbers after sorting the volume numbers. Thus, all the page numbers for Volume I are sorted in order before the page numbers for Volume II. Finally, we pipe the output to uniq to remove identical entries. Processing the output from input.idx , the sort command produces:

graphics:CANVAS_X_PAINT_WINDOW:86
graphics:XView model:83
graphics:~zz(see also server image):
header file:Xlib.h:89 
macro:XV_INIT_ARGS:46
toolkit:(See X Window System).:
type:Xv_object:49
type:Xv_singlecolor:80
X Window System:events:84
X Window System:X Window ID for paint window:87
Xlib:repainting canvas:88
Xlib.h header file::89 
XView:programs; initialization:45
XV_INIT_ARGS macro::46
Xv_object type::49
Xv_singlecolor type::80

12.2.4 Handling Page Numbers

The pagenums.idx program looks for entries that differ only in page number and creates a list of page numbers for a single entry. The input to this program is four colon-separated fields:

PRIMARY:SECONDARY:PAGE:VOLUME

The fourth is optional. For now, we consider only the index for a single book, in which there are no volume numbers. Remember that the entries are now sorted.

The heart of this program compares the current entry to the previous one and determines what to output. The conditionals that implement the comparison can be extracted and expressed in pseudocode, as follows:

PRIMARY = $1
SECONDARY = $2
PAGE = $3
if (PRIMARY == prevPRIMARY)
	if (SECONDARY == prevSECONDARY)
		print PAGE
	else
		print PRIMARY:SECONDARY:PAGE
else
	print PRIMARY:SECONDARY:PAGE
prevPRIMARY = PRIMARY
prevSECONDARY = SECONDARY

Let's see how this code handles a series of entries, beginning with:

XView::18

The primary key doesn't match the previous primary key; the line is output as is:

XView::18

The next entry is:

XView:about:3

When we compare the primary key of this entry to the previous one, they are the same. When we compare secondary keys, they differ; we output the record as is:

XView:about:3

The next entry is:

XView:about:7

Because both the primary and secondary keys match the keys of the previous entry, we simply output the page number. (The printf function is used instead of print so that there is no automatic newline.) This page number is appended to the previous entry so that it looks like this:

XView:about:3,7

The next entry also matches both keys:

XView:about:10

Again, only the page number is output so that entry now looks like:

XView:about:3,7,10

In this way, three entries that differ only in page number are combined into a single entry.

The full script adds an additional test to see if the volume identifier matches. Here's the full pagenums.idx script:

#!/work/bin/nawk -f
# ------------------------------------------------
# pagenums.idx -- collect pages for common entries 
# Author:  Dale Dougherty
# Version 1.1   7/10/90
# 
# input should be PRIMARY:SECONDARY:PAGE:VOLUME
# ------------------------------------------------

BEGIN { FS = ":"; OFS = ""}

# main routine -- apply to all input lines
{
   # assign fields to variables
	PRIMARY = $1
	SECONDARY = $2
	PAGE = $3
	VOLUME = $4

   # check for a see also and collect it in array
	if (SECONDARY ~ /\([Ss]ee +[Aa]lso/) {
	# create tmp copy & remove "~zz" from copy 
		tmpSecondary = SECONDARY
		sub(/~zz\([Ss]ee +[Aa]lso */, "", tmpSecondary)
		sub(/\) */, "", tmpSecondary)
	# remove secondary key along with "~zz"
		sub(/^.*~zz\([Ss]ee +[Aa]lso */, "", SECONDARY)
		sub(/\) */, "", SECONDARY)
	# assign to next element of seeAlsoList
		seeAlsoList[++eachSeeAlso] = SECONDARY "; "
		prevPrimary = PRIMARY
	# assign copy to previous secondary key
		prevSecondary = tmpSecondary 
		next
	} # end test for see Also

   # Conditionals to compare keys of current record to previous
   #  record.  If Primary and Secondary keys are the same, only
   #  the page number is printed. 

   # test to see if each PRIMARY key matches previous key
	if (PRIMARY == prevPrimary) {
	# test to see if each SECONDARY key matches previous key
		if (SECONDARY == prevSecondary)
		# test to see if VOLUME matches;
		# print only VOLUME:PAGE
			if (VOLUME == prevVolume)
				printf (",%s", PAGE)
			else {
				printf ("; ")
				volpage(VOLUME, PAGE)
			}
		else{
		# if array of See Alsos, output them now
			if (eachSeeAlso) outputSeeAlso(2)
		# print PRIMARY:SECONDARY:VOLUME:PAGE
			printf ("\n%s:%s:", PRIMARY, SECONDARY)
			volpage(VOLUME, PAGE)
		}
	} # end of test for PRIMARY == prev
	else { # PRIMARY != prev
		# if we have an array of See Alsos, output them now
		if (eachSeeAlso) outputSeeAlso(1)
		if (NR != 1) 
			printf ("\n")
		if (NF == 1){
			printf ("%s:", $0)
		}
		else {
			printf ("%s:%s:", PRIMARY, SECONDARY)
			volpage(VOLUME, PAGE)
		}
	}
   	prevPrimary = PRIMARY
	prevSecondary = SECONDARY
	prevVolume = VOLUME

} # end of main routine

# at end, print newline
END { 
   # in case last entry has "see Also"
	if (eachSeeAlso) outputSeeAlso(1)
	printf("\n")
}

# outputSeeAlso function -- list elements of seeAlsoList 
function outputSeeAlso(LEVEL) {
	# LEVEL - indicates which key we need to output
	if (LEVEL == 1)
		printf ("\n%s:(See also ", prevPrimary)
	else {
		sub(/;.*$/, "", prevSecondary)
		printf ("\n%s:%s; (See also ", prevPrimary, prevSecondary)
	}
	sub(/; $/, ".):", seeAlsoList[eachSeeAlso])
	for (i = 1; i <= eachSeeAlso; ++i)
		printf ("%s", seeAlsoList[i]) 
	eachSeeAlso = 0
}

# volpage function -- determine whether or not to print volume info 
# 	two args: volume & page
 
function volpage(v, p)
{
   # if VOLUME is empty then print PAGE only 
	if ( v == "" ) 
		printf ("%s", p)
	else
   # otherwise print VOLUME^PAGE
		printf ("%s^%s",v, p)  
}

Remember, first of all, that the input to the program is sorted by its keys. The page numbers are also in order, such that an entry for "graphics" on page 7 appears in the input before one on page 10. Similarly, entries for Volume I appear in the input before Volume II. Therefore, this program need do no sorting; it simply compares the keys and if they are the same, appends the page number to a list. In this way, the entries are reduced.

This script also handles "see also" entries. Since the records are now sorted, we can remove the special sorting sequence "~zz." We also handle the case where we might encounter consecutive "see also" entries. We don't want to output:

Toolkit (see also Xt) (See also XView) (See also Motif).

Instead we'd like to combine them into a list such that they appear as:

Toolkit (see also Xt; XView; Motif)

To do that, we create an array named seeAlsoList . From SECONDARY , we remove the parentheses, the secondary key if it exists and the "see also" and then assign it to an element of seeAlsoList . We make a copy of SECONDARY with the secondary key and assign it to prevSecondary for making comparisons to the next entry.

The function outputSeeAlso() is called to read all the elements of the array and print them. The function volpage() is also simple and determines whether or not we need to output a volume number. Both of these functions are called from more than one place in the code, so the main reason for defining them as functions is to reduce duplication.

Here's an example of what it produces for a single-book index:

X Window System:Xlib:6
XFontStruct structure::317
Xlib::6
Xlib:repainting canvas:88
Xlib.h header file::89,294
Xv_Font type::310
XView::18
XView:about:3,7,10
XView:as object-oriented system:17

Here's an example of what it produces for a master index:

reserved names:table of:I^43
Xt:example of programming interface:I^44,65
Xt:objects; list of:I^43,58; II^40
Xt:packages:I^43,61; II^42
Xt:programs; initialization:I^45
Xt:reserved names:I^43,58
Xt:reserved prefixes:I^43,58
Xt:types:I^43,54,61

The "^" is used as a temporary delimiter between the volume number and the list of page numbers.

12.2.5 Merging Entries with the Same Keys

The pagenums.idx program reduced entries that were the same except for the page number. Now we'll to process entries that share the same primary key. We also want to look for consecutive page numbers and combine them in ranges.

The combine.idx is quite similar to the pagenums.idx script, making another pass through the index, comparing entries with the same primary key. The following pseudocode abstracts this comparison. (To make this discussion easier, we will omit tertiary keys and show how to compare primary and secondary keys.) After the entries are processed by pagenums.idx , no two entries exist that share the same primary and secondary keys. Therefore, we don't have to compare secondary keys.

PRIMARY = $1
SECONDARY = $2
PAGE = $3
if (PRIMARY == prevPRIMARY)
	print :SECONDARY:
else
	print PRIMARY:SECONDARY
prevPRIMARY = PRIMARY
prevSECONDARY = SECONDARY

If the primary keys match, we output only the secondary key. For instance, if there are three entries:

XView:18
XView:about:3, 7, 10
XView:as object-oriented system:17

they will be output as:

XView:18
:about:3, 7, 10
:as object-oriented system:17

We drop the primary key when it is the same. The actual code is a little more difficult because there are tertiary keys. We have to test primary and secondary keys to see if they are unique or the same, but we don't have to test tertiary keys. (We only need to know that they are there.)

You no doubt noticed that the above pseudocode does not output page numbers. The second role of this script is to examine page numbers and combine a list of consecutive numbers. The page numbers are a comma-separated list that can be loaded into an array, using the split() function.

To see if numbers are consecutive, we loop through the array comparing each element to 1 + the previous element.

eachpage[j-1]+1 == eachpage[j]

In other words, if adding 1 to the previous element produces the current element, then they are consecutive. The previous element becomes the first page number in the range and the current element becomes the last page in the range. This is done within a while loop until the conditional is not true, and the page numbers are not consecutive. Then we output the first page number and the last page number separated by a hyphen:

23-25

The actual code looks more complicated than this because it is called from a function that must recognize volume and page number pairs. It first has to split the volume from the list of page numbers and then it can call the function ( rangeOfPages() ) to process the list of numbers.

Here is the full listing of combine.idx :

#!/work/bin/nawk -f
# ------------------------------------------------
# combine.idx -- merge keys with same PRIMARY key
#		and combine consecutive page numbers
# Author:  Dale Dougherty
# Version 1.1   7/10/90
# 
# input should be PRIMARY:SECONDARY:PAGELIST
# ------------------------------------------------

BEGIN   { FS = ":"; OFS = ""}
# main routine -- applies to all input lines
#  It compares the keys and merges the duplicates.
{
   # assign first field
	PRIMARY=$1
   # split second field, getting SEC and TERT keys.
	sizeOfArray = split($2, array, ";") 
	SECONDARY = array[1]
	TERTIARY = array[2]
   # test that tertiary key exists
	if (sizeOfArray > 1) {
	# tertiary key exists
		isTertiary = 1 
	# two cases where ";" might turn up
	# check SEC key for list of "see also" 
		if (SECONDARY ~ /\([sS]ee also/){
			SECONDARY = $2
			isTertiary = 0
		}
	# check TERT key for "see also" 
		if (TERTIARY ~ /\([sS]ee also/){
			TERTIARY = substr($2, (index($2, ";") + 1))
		}	
	}
	else # tertiary key does not exist
		isTertiary = 0
   # assign third field
	PAGELIST = $3

   # Conditional to compare primary key of this entry to that
   #  of previous entry. Then compare secondary keys.  This 
   #  determines which non-duplicate keys to output.
	if (PRIMARY == prevPrimary) {
		if (isTertiary && SECONDARY == prevSecondary)
			printf (";\n::%s", TERTIARY)
		else
			if (isTertiary)
				printf ("\n:%s; %s", SECONDARY, TERTIARY)
			else
				printf ("\n:%s", SECONDARY)
	 }
	 else {
		if (NR != 1) 
			printf ("\n")
		if ($2 != "") 
			printf ("%s:%s", PRIMARY, $2)
		else 
			printf ("%s", PRIMARY)

		prevPrimary = PRIMARY
	}

	prevSecondary = SECONDARY
} # end of main procedure

# routine for "See" entries (primary key only)
NF == 1 { printf ("\n") }

# routine for all other entries
#  It handles output of the page number.

NF > 1  {
	if (PAGELIST)
	# calls function numrange() to look for 
 	# consecutive page numbers.
		printf (":%s", numrange(PAGELIST))  
	else
		if (! isTertiary || (TERTIARY && SECONDARY)) printf (":")  

} # end of NF > 1

# END procedure outputs newline
END {  printf ("\n") }

# Supporting Functions

# numrange -- read list of Volume^Page numbers, detach Volume
#		from Page for each Volume and call rangeOfPages 
#		to combine consecutive page numbers in the list. 
#	PAGE = volumes separated by semicolons; volume and page
#		separated by ^.

function numrange(PAGE,     listOfPages, sizeOfArray)
{
  # Split up list by volume.
	sizeOfArray = split(PAGE, howManyVolumes,";") 
  # Check to see if more than 1 volume.
	if (sizeOfArray > 1) {

	# if more than 1 volume, loop through list 
		for (i = 1; i <= sizeOfArray; ++i) {
		# for each Volume^Page element, detach Volume 
		# and call rangeOfPages function on Page to
		# separate page numbers and compare to find
		# consecutive numbers.
			if (split(howManyVolumes[i],volPage,"^") == 2)  
				listOfPages = volPage[1] "^"
				   rangeOfPages(volPage[2])
		# collect output in listOfPages
			if (i == 1) 
				result = listOfPages
			else
				result=result ";" listOfPages
		} # end for loop
	}
	else { # not more than 1 volume

	# check for single volume index with volume number 
	# if so, detach volume number.
	# Both call rangeOfPages on the list of page numbers.
		if (split(PAGE,volPage,"^") == 2 )  
		# if Volume^Page, detach volume and then call rangeOfPages 
			listOfPages = volPage[1] "^" rangeOfPages(volPage[2])
		else # No volume number involved 
			listOfPages = rangeOfPages(volPage[1])
		result = listOfPages
	} # end of else

	return result  # Volume^Page list

} # End of numrange function

# rangeOfPages -- read list of comma-separated page numbers,  
#		load them into an array, and compare each one
#		to the next, looking for consecutive numbers.
#	PAGENUMBERS = comma-separated list of page numbers

function rangeOfPages(PAGENUMBERS, pagesAll, sizeOfArray,pages,
                       listOfPages, d, p, j) {
   # close-up space on troff-generated ranges
	gsub(/ - /, ",-", PAGENUMBERS)

   # split list up into eachpage array.
	sizeOfArray = split(PAGENUMBERS, eachpage, ",")
   # if more than 1 page number
	if (sizeOfArray > 1){
	# for each page number, compare it to previous number + 1
		p = 0  # flag indicates assignment to pagesAll 
	# for loop starts at 2
		for (j = 2; j-1 <= sizeOfArray; ++j) {
		# start by saving first page in sequence (firstpage)    
		# and loop until we find last page (lastpage)
			firstpage = eachpage[j-1]
			d = 0  # flag indicates consecutive numbers found  
		# loop while page numbers are consecutive
			while ((eachpage[j-1]+1) == eachpage[j] ||
					eachpage[j] ~ /^-/) {
			# remove "-" from troff-generated range
				if (eachpage[j] ~ /^-/) {
					sub(/^-/, "", eachpage[j])
				}
				lastpage = eachpage[j]
			# increment counters
				++d
				++j
			} # end of while loop
		# use values of firstpage and lastpage to make range.
			if (d >= 1) {
			# there is a range
				pages = firstpage "-" lastpage 
			}
			else # no range; only read firstpage 
				pages = firstpage 
		# assign range to pagesAll 
			if (p == 0) {
				pagesAll = pages 
				p = 1
			}
			else {
				pagesAll = pagesAll "," pages
			}
		}# end of for loop

	# assign pagesAll to listOfPages
		listOfPages = pagesAll

	} # end of sizeOfArray > 1

	else # only one page 
		listOfPages = PAGENUMBERS

   # add space following comma
	gsub(/,/, ", ", listOfPages)
   # return changed list of page numbers
	return listOfPages
} # End of rangeOfPages function

This script consists of minimal BEGIN and END procedures. The main routine does the work of comparing primary and secondary keys. The first part of this routine assigns the fields to variables. The second field contains the secondary and tertiary keys and we use split() to separate them. Then we test that there is a tertiary key and set the flag isTertiary to either 1 or 0.

The next part of the main procedure contains the conditional expressions that look for identical keys. As we said in our discussion of the pseudocode for this part of the program, entries with wholly identical keys have already been removed by the pagenums.idx .

The conditionals in this procedure determine what keys to output based on whether or not each is unique. If the primary key is unique, it is output, along with the rest of the entry. If the primary key matches the previous key, we compare secondary keys. If the secondary key is unique, then it is output, along with the rest of the entry. If the primary key matches the previous primary key, and the secondary key matches the previous secondary key, then the tertiary key must be unique. Then we only output the tertiary key, leaving the primary and secondary keys blank.

The different forms are shown below:

primary
primary:secondary
:secondary
:secondary:tertiary
::tertiary
primary:secondary:tertiary

The main procedure is followed by two additional routines. The first of them is executed only when NF equals one. It deals with the first of the forms on the list above. That is, there is no page number so we must output a newline to finish the entry.

The second procedure deals with all entries that have page numbers. This is the procedure where we call a function to take apart the list of page numbers and look for consecutive pages. It calls the numrange() function, whose main purpose is to deal with a multivolume index where a list of page numbers might look like:

I^35,55; II^200

This function calls split() using a semicolon delimiter to separate each volume. Then we call split() using a "^" delimiter to detach the volume number from the list of page numbers. Once we have the list of pages, we call a second function rangeOfPages() to look for consecutive numbers. On a single-book index, such as the sample shown in this chapter, the numrange() function really does nothing but call rangeOfPages() . We discussed the meat of the rangeOfPages() function earlier. The eachpage array is created and a while loop is used to go through the array comparing an element to the one previous. This function returns the list of pages.

Sample output from this program follows:

Xlib:6
:repainting canvas:88
Xlib.h header file:89, 294
Xv_Font type:310
XView:18
:about:3, 7, 10
:as object-oriented system:17
:compiling programs:41
:concept of windows differs from X:25
:data types;  table of:20
:example of programming interface:44
:frames and subframes:26
:generic functions:21
:Generic Object:18, 24
:libraries:42
:notification:10, 35
:objects:23-24;
:: table of:20;
:: list of:43
:packages:18, 43
:programmer's model:17-23
:programming interface:41
:programs;  initialization:45
:reserved names:43
:reserved prefixes:43
:structure of applications:41
:subwindows:28
:types:43
:window objects:25

In particular, notice the entry for "objects" under "XView." This is an example of a secondary key with multiple tertiary keys. It is also an example of an entry with a consecutive page range.

12.2.6 Formatting the Index

The previous scripts have done nearly all of the processing, leaving the list of entries in good order. The format.idx script, probably the easiest of the scripts, reads the list of entries and generates a report in two different formats, one for display on a terminal screen and one to send to troff for printing on a laser printer. Perhaps the only difficulty is that we output the entries grouped by each letter of the alphabet.

A command-line argument sets the variable FMT that determines which of the two output formats is to be used.

Here's the full listing for format.idx :

#!/work/bin/nawk -f
# ------------------------------------------------
# format.idx -- prepare formatted index
# Author:  Dale Dougherty
# Version 1.1   7/10/90
# 
# input should be PRIMARY:SECONDARY:PAGE:VOLUME
# Args:  FMT = 0 (default) format for screen
#        FMT = 1 output with troff macros
#        MACDIR = pathname of index troff macro file 
# ------------------------------------------------
BEGIN {		FS = ":"
		upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
		lower = "abcdefghijklmnopqrstuvwxyz" 
}

# Output initial macros if troff FMT 
NR == 1 && FMT == 1 {
		if (MACDIR)
			printf (".so %s/indexmacs\n", MACDIR) 
		else
			printf (".so indexmacs\n") 
		printf (".Se \"\" \"Index\"\n") 
		printf (".XC\n") 
} # end of NR == 1
 

# main routine - apply to all lines
# determine which fields to output
{
   # convert octal colon to "literal" colon 
   # make sub for each field, not $0, so that fields are not parsed
	gsub(/\\72/, ":", $1)
	gsub(/\\72/, ":", $2)
	gsub(/\\72/, ":", $3)

   # assign field to variables
	PRIMARY = $1
	SECONDARY = $2
	TERTIARY = ""
	PAGE = $3
	if (NF == 2) {
		SECONDARY = ""
		PAGE = $2
	}
   # Look for empty fields to determine what to output
	if (! PRIMARY) {  
		if (! SECONDARY) {
			TERTIARY = $3
			PAGE = $4	
			if (FMT == 1)
				printf (".XF 3 \"%s", TERTIARY)
			else
				printf ("  %s", TERTIARY)
		}
		else
		        if (FMT == 1)
			        printf (".XF 2 \"%s", SECONDARY)
		        else
			        printf ("  %s", SECONDARY)
	}
	else { # if primary entry exists	
	     # extract first char of primary entry
		firstChar = substr($1, 1, 1)
	     # see if it is in lower string.
		char = index(lower, firstChar) 
	     # char is an index to lower or upper letter 
		if (char == 0)  {
		# if char not found, see if it is upper
			char = index(upper, firstChar)
			if (char == 0)
				char = prevChar
		}
		# if new char, then start group for new letter of alphabet
		if (char != prevChar) {
			if (FMT == 1)
				printf(".XF A \"%s\"\n", substr(upper, char, 1))
			else
				printf("\n\t\t%s\n", substr(upper, char, 1))
			prevChar = char
		}
		# now output primary and secondary entry
		if (FMT == 1)
			if (SECONDARY)
				printf (".XF 1 \"%s\" \"%s", PRIMARY, SECONDARY)
			else
				printf (".XF 1 \"%s\" \"", PRIMARY)
		else
			if (SECONDARY)
				printf ("%s, %s", PRIMARY, SECONDARY)
			else
				printf ("%s", PRIMARY)
	}
	
   # if page number, call pageChg to replace "^" with ":"
   # for multi-volume page lists.
	if (PAGE) {
		if (FMT == 1) {
			# added to omit comma after bold entry
			if (! SECONDARY && ! TERTIARY)
				printf ("%s\"", pageChg(PAGE))
			else
				printf (", %s\"", pageChg(PAGE))
		}
		else
			printf (", %s", pageChg(PAGE))
	}
	else if (FMT == 1)
		printf("\"")
	
	printf ("\n")

} # End of main routine

# Supporting function

# pageChg -- convert "^" to ":" in list of volume^page 
#	Arg: pagelist -- list of numbers 

function pageChg(pagelist) {
	 gsub(/\^/, ":", pagelist)
	 if (FMT == 1) {
		gsub(/[1-9]+\*/, "\\fB&\\P", pagelist)
		gsub(/\*/, "", pagelist)
	}
	return pagelist
}# End of pageChg function

The BEGIN procedure defines the field separator and the strings upper and lower . The next procedure is one that outputs the name of the file that contains the troff index macro definitions. The name of the macro directory can be set from the command line as the second argument.

The main procedure begins by converting the "hidden" colon to a literal colon. Note that we apply the gsub() function to each field rather than the entire line because doing the latter would cause the line to be reevaluated and the current order of fields would be disturbed.

Next we assign the fields to variables and then test to see whether the field is empty. If the primary key is not defined, then we see if the secondary key is defined. If it is, we output it. If it is not, then we output a tertiary key. If the primary key is defined, then we extract its first character and then see if we find it in the lower string.

firstChar = substr($1, 1, 1)
     
char = index(lower, firstChar)

The char variable holds the position of the letter in the string. If this number is greater than or equal to 1, then we also have an index into the upper string. We compare each entry and while char and prevChar are the same, the current letter of the alphabet is unchanged. Once they differ, first we check for the letter in the upper string. If char is a new letter, we output a centered string that identifies that letter of the alphabet.

Then we look at outputting the primary and secondary entries. Finally, the list of page numbers is output, after calling the pageChg() function to replace the "^" in volume-page references with a colon.

Sample screen output produced by format.idx is shown below:

            X
X Protocol, 6
X Window System, events, 84
  extensibility, 9
  interclient communications, 9
  overview, 3
  protocol, 6
  role of window manager, 9
  server and client relationship, 5
  software hierarchy, 6
  toolkits, 7
  X Window ID for paint window, 87
  Xlib, 6
XFontStruct structure, 317
Xlib, 6
  repainting canvas, 88
Xlib.h header file, 89, 294
Xv_Font type, 310
XView, 18
  about, 3, 7, 10
  as object-oriented system, 17
  compiling programs, 41
  concept of windows differs from X, 25
  data types;  table of, 20
  example of programming interface, 44
  frames and subframes, 26
  generic functions, 21
  Generic Object, 18, 24

Sample troff output produced by format.idx is shown below:

.XF A "X"
.XF 1 "X Protocol" "6"
.XF 1 "X Window System" "events, 84"
.XF 2 "extensibility, 9"
.XF 2 "interclient communications, 9"
.XF 2 "overview, 3"
.XF 2 "protocol, 6"
.XF 2 "role of window manager, 9"
.XF 2 "server and client relationship, 5"
.XF 2 "software hierarchy, 6"
.XF 2 "toolkits, 7"
.XF 2 "X Window ID for paint window, 87"
.XF 2 "Xlib, 6"
.XF 1 "XFontStruct structure" "317"
.XF 1 "Xlib" "6"
.XF 2 "repainting canvas, 88"
.XF 1 "Xlib.h header file" "89, 294"
.XF 1 "Xv_Font type" "310"
.XF 1 "XView" "18"
.XF 2 "about, 3, 7, 10"
.XF 2 "as object-oriented system, 17"

This output must be formatted by troff to produce a printed version of the index. The index of this book was originally done using the masterindex program.

12.2.6.1 The masterindex shell script

The masterindex shell script is the glue that holds all of these scripts together and invokes them with the proper options based on the user's command line. For instance, the user enters:

$ 

masterindex -s -m volume1 volume2 

to specify that a master index be created from the files volume1 and volume2 and that the output be sent to the screen.

The masterindex shell script is presented in Appendix C with the documentation.


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