Add double-pipe syntax in LESSOPEN to use exit status.

ch.c

@@ -582,6 +582,8 @@ ch_length()
  return (NULL_POSITION);
  if (ch_flags & CH_HELPFILE)
  return (size_helpdata);
+ if (ch_flags & CH_NODATA)
+ return (0);
  return (ch_fsize);
 }
 

edit.c

@@ -310,6 +310,10 @@ edit_ifile(ifile)
  */
  __djgpp_set_ctrl_c(1);
 #endif
+ } else if (strcmp(open_filename, FAKE_EMPTYFILE) == 0)
+ {
+ f = -1;
+ chflags |= CH_NODATA;
  } else if (strcmp(open_filename, FAKE_HELPFILE) == 0)
  {
  f = -1;

filename.c

@@ -832,7 +832,7 @@ open_altfile(filename, pf, pfd)
  ch_ungetchar(-1);
  if ((lessopen = lgetenv("LESSOPEN")) == NULL)
  return (NULL);
- if (*lessopen == '|')
+ while (*lessopen == '|')
  {
  /*
  * If LESSOPEN starts with a |, it indicates 
@@ -843,7 +843,7 @@ open_altfile(filename, pf, pfd)
  return (NULL);
 #else
  lessopen++;
- returnfd = 1;
+ returnfd++;
 #endif
  }
  if (*lessopen == '-') {
@@ -883,9 +883,18 @@ open_altfile(filename, pf, pfd)
  if (read(f, &c, 1) != 1)
  {
  /*
- * Pipe is empty. This means there is no alt file.
+ * Pipe is empty.
+ * If more than 1 pipe char was specified,
+ * the exit status tells whether the file itself 
+ * is empty, or if there is no alt file.
+ * If only one pipe char, just assume no alt file.
  */
- pclose(fd);
+ int status = pclose(fd);
+ if (returnfd > 1 && status == 0) {
+ *pfd = NULL;
+ *pf = -1;
+ return (save(FAKE_EMPTYFILE));
+ }
  return (NULL);
  }
  ch_ungetchar(c);

less.h

@@ -485,10 +485,13 @@ struct textlist
 #define CH_KEEPOPEN 002
 #define CH_POPENED 004
 #define CH_HELPFILE 010
+#define CH_NODATA 020 /* Special case for zero length files */
+
 
 #define ch_zero() ((POSITION)0)
 
 #define FAKE_HELPFILE "@/\\less/\\help/\\file/\\@"
+#define FAKE_EMPTYFILE "@/\\less/\\empty/\\file/\\@"
 
 /* Flags for cvt_text */
 #define CVT_TO_LC 01 /* Convert upper-case to lower-case */

less.nro.VER

@@ -1161,14 +1161,33 @@ lesspipe.sh:
  case "$1" in
 .br
  *.Z) uncompress \-c $1 2>/dev/null
+.br
+ *) exit 1
 .br
  ;;
 .br
  esac
+.br
+ exit $?
 .br
 .PP
 To use this script, put it where it can be executed and set
 LESSOPEN="|lesspipe.sh %s".
+.PP
+Note that a preprocessor cannot output an empty file, since that
+is interpreted as meaning there is no replacement, and 
+the original file is used.
+To avoid this, if LESSOPEN starts with two vertical bars,
+the exit status of the script becomes meaningful.
+If the exit status is zero, the output is considered to be 
+replacement text, even if it empty.
+If the exit status is nonzero, any output is ignored and the
+original file is used.
+For compatibility with previous versions of
+.I less,
+if LESSOPEN starts with only one vertical bar, the exit status
+of the preprocessor is ignored.
+.PP
 When an input pipe is used, a LESSCLOSE postprocessor can be used,
 but it is usually not necessary since there is no replacement file
 to clean up.
@@ -1187,7 +1206,8 @@ the preprocessor command.
 If standard input is being viewed, the input preprocessor is passed
 a file name consisting of a single dash.
 Similarly, if the first two characters of LESSOPEN are vertical bar and dash
-(|\-), the input pipe is used on standard input as well as other files.
+(|\-) or two vertical bars and a dash (||\-), 
+the input pipe is used on standard input as well as other files.
 Again, in this case the dash is not considered to be part of 
 the input pipe command.