txt-from-texi: add support for variables

The support for variables in the text-from-texi script is used to
automatically insert the current version of Window Maker, inherited from
the definition in the AC_INIT command, so it will be always correctly
updated without the need for hand work.

Having this version information is recommended by GNU texinfo because if
the document happens to get distributed outside a package it can help user
avoid problems.

The second use is to define a variable 'emailsupport' which contains the
email address of the development team, so we can also inherit it from the
AC_INIT setting.

The third use is for a special variable 'cctexi2txt' to differentiate
between texi2any and our script, because when using texi2any the title
page is not generated, so we need to duplicate some information in the
source, but we do not want it to appear twice in our generated doc.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

script/generate-txt-from-texi.sh

@@ -97,6 +97,8 @@ print_help() {
     echo "$0: convert a Texinfo file into a plain text file"
     echo "Usage: $0 [options...] file.texi"
     echo "valid options are:"
+    echo "  -Dvar=val  : set variable 'var' to value 'val'"
+    echo "  -e email   : set email address in variable 'emailsupport'"
     echo "  -v version : version of the project"
     echo "  -o file    : name of text file to create"
     exit 0
@@ -106,6 +108,18 @@ print_help() {
 while [ $# -gt 0 ]; do
     case $1 in
 
+        -D*)
+            echo "$1" | grep '^-D[a-zA-Z][a-zA-Z]*=' > /dev/null || arg_error "syntax error for '$1', expected -Dname=value"
+            var_defs="$var_defs
+`echo "$1" | sed -e 's/^-D/  variable["/ ; s/=/"] = "/ ; s/$/";/' `"
+          ;;
+
+        -e)
+            shift
+            var_defs="$var_defs
+  variable[\"emailsupport\"] = \"@email{`echo "$1" | sed -e 's/@/@@/g' `}\";"
+          ;;
+
         -h|-help|--help) print_help ;;
 
         -o)
@@ -181,6 +195,17 @@ function end_conditional(name,          local_i) {
   }
 }
 
+# Texinfo Variables
+# the texinfo standard allows to have variables set with @set and used
+# with @value; they can also be defined from command-line (-D)
+# they are stored in the global array "variable[name]"
+function set_variable(line,          local_split, local_idx) {
+  local_idx = match(line, /^([^ \t]+)([ \t]*)(.*)$/, local_split);
+  if (local_idx > 0) {
+    variable[ local_split[1] ] = local_split[3];
+  }
+}
+
 # Write a single line to the output
 function write_line(line) {
   if (!cond_state) { return; }
@@ -724,6 +749,14 @@ function execute_commands(line,               replaced_line) {
       replaced_line = replaced_line generate_url_reference(cmdargs);
       break;
 
+    # Variable and Conditional commands ########################################
+    case "value":
+      if (variable[cmdargs] == "") {
+        report_error("variable '" cmdargs "' is unknow, for @value at line " NR);
+      }
+      line = variable[cmdargs] line;
+      break;
+
     # Miscelleanous commands ###################################################
     case "c":
       # Comments: ignore everything to the end of line
@@ -816,6 +849,12 @@ BEGIN {
   # Number of entries in the Table of Content
   toc_count = 0;
   toc_file = "'"$toc_file"'";
+
+  # Define a custom variable so it is possible to differentiate between
+  # texi2any and this script
+  variable["cctexi2txt"] = "1.0";
+
+  # Variables inherited from the command line'"$var_defs"'
 }
 
 # First line is special, we always ignore it
@@ -1005,6 +1044,21 @@ BEGIN {
     case "ifnottex":       start_conditional(command[1], 1); line = ""; next;
     case "ifnotxml":       start_conditional(command[1], 1); line = ""; next;
 
+    case "ifclear": start_conditional(command[1], (variable[line] == "")); next;
+    case "ifset":   start_conditional(command[1], (variable[line] != "")); next;
+
+    case "clear":
+      if (cond_state) {
+        variable[ execute_commands(line) ] = "";
+      }
+      next;
+
+    case "set":
+      if (cond_state) {
+        set_variable(execute_commands(line));
+      }
+      next;
+
     # Miscelleanous commands ###################################################
     case "bye":
       # Mark the end of file, we are supposed to ignore everything after