Add += syntax to variable section in lesskey files.

NEWS

@@ -24,6 +24,8 @@
 
 * Add #version conditional to lesskey.
 
+* Add += syntax to variable section in lesskey files.
+
 * Allow option name in -- command to end with '=' in addition to '\n'.
 
 * Don't read or write history file in secure mode.

lesskey.nro.VER

@@ -337,23 +337,15 @@ Variables assigned in this way are visible only to
 .IR less .
 If a variable is specified in the system environment and also in a
 lesskey file, the value in the lesskey file takes precedence.
-Although the lesskey file can be used to override variables set in the
-environment, the main purpose of assigning variables in the lesskey file
-is simply to have all
-.I less
-configuration information stored in one file.
 .
-.SH EXAMPLE
-The following input file sets the \-i option whenever
-.I less
-is run, and specifies the character set to be "latin1":
-.sp
-.nf
- #env
- LESS = \-i
- LESSCHARSET = latin1
-.fi
 .sp
+If the variable name is followed by += rather than =,
+the string is appended to the variable's existing value.
+This currently works only if any += lines immediately follow
+the same variable's original definition (with an = line),
+without any intervening definitions of other variables.
+It can append only to a variable defined earlier in the file;
+it cannot append to a variable in the system environment.
 .
 .SH CONDITIONAL CONFIGURATION
 If a line begins with #version followed by a relational operator and a version number,
@@ -393,9 +385,20 @@ The #version feature is not supported in
 .I less
 and
 .I lesskey
-version 594 and earlier.
+before version 594.
 In those older versions, all #version lines are ignored.
 .
+.SH EXAMPLE
+The following input file sets the \-i and \-S options when
+.less
+is run and, on version 595 and higher, adds a \-\-color option.
+.sp
+.nf
+ #env
+ LESS = \-i\ \-S
+ #version\ >=\ 595\ \ LESS\ +=\ \-\-color=Hkc
+.fi
+.
 .SH "SEE ALSO"
 .BR less (1)
 .

lesskey_parse.c

@@ -355,6 +355,13 @@ add_cmd_char(c, tables)
  xbuf_add(&tables->currtable->buf, c);
 }
 
+ static void
+erase_cmd_char(tables)
+ struct lesskey_tables *tables;
+{
+ xbuf_pop(&tables->currtable->buf);
+}
+
 /*
  * Add a string to the output command table.
  */
@@ -567,26 +574,37 @@ parse_varline(line, tables)
 {
  char *s;
  char *p = line;
+ char *eq;
 
- do
+ eq = strchr(line, '=');
+ if (eq != NULL && eq > line && eq[-1] == '+')
  {
- s = tstr(&p, 0);
- add_cmd_str(s, tables);
- } while (*p != '\0' && !issp(*p) && *p != '=');
- /*
- * Terminate the variable name with a null byte.
- */
- add_cmd_char('\0', tables);
-
- p = skipsp(p);
- if (*p++ != '=')
+ /*
+ * Rather ugly way of handling a += line.
+ * {{ Note that we ignore the variable name and 
+ * just append to the previously defined variable. }}
+ */
+ erase_cmd_char(tables); /* backspace over the final null */
+ p = eq+1;
+ } else
  {
- parse_error("missing = in variable definition", "");
- return;
+ do
+ {
+ s = tstr(&p, 0);
+ add_cmd_str(s, tables);
+ } while (*p != '\0' && !issp(*p) && *p != '=');
+ /*
+ * Terminate the variable name with a null byte.
+ */
+ add_cmd_char('\0', tables);
+ p = skipsp(p);
+ if (*p++ != '=')
+ {
+ parse_error("missing = in variable definition", "");
+ return;
+ }
+ add_cmd_char(EV_OK|A_EXTRA, tables);
  }
-
- add_cmd_char(EV_OK|A_EXTRA, tables);
-
  p = skipsp(p);
  while (*p != '\0')
  {

version.c

@@ -937,7 +937,7 @@ v592 8/24/21 Add --status-line option; limit use of /proc kludge; add --heade
 v593 8/30/21 Add header columns, --no-number-headers.
 v594 Let regex library handle caseless; add --redraw-on-quit option;
  add #version to lesskey.
-v595
+v595 Add H color type; add += to lesskey var section.
 */
 
 char version[] = "595x";

xbuf.c

@@ -50,3 +50,12 @@ xbuf_add(xbuf, ch)
  }
  xbuf->data[xbuf->end++] = ch;
 }
+
+ public int
+xbuf_pop(buf)
+ struct xbuffer *buf;
+{
+ if (buf->end == 0)
+ return -1;
+ return buf->data[--(buf->end)];
+}

xbuf.h

@@ -11,5 +11,6 @@ struct xbuffer
 void xbuf_init(struct xbuffer *xbuf);
 void xbuf_reset(struct xbuffer *xbuf);
 void xbuf_add(struct xbuffer *xbuf, int ch);
+int xbuf_pop(struct xbuffer *xbuf);
 
 #endif