less/less-436-empty-lessopen-pipe.patch

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diff -rup less-436-orig/filename.c less-436/filename.c
--- less-436-orig/filename.c 2009-07-06 22:52:23.000000000 +0200
+++ less-436/filename.c 2011-02-09 16:36:59.508940154 +0100
@@ -843,6 +843,16 @@ open_altfile(filename, pf, pfd)
#else
lessopen++;
returnfd = 1;
+
+ if (*lessopen == '|') {
+ /*
+ * If there is another vertical bar |, after
+ * the first one, it indicates a "pipe preprocessor"
+ * with correct exit status.
+ */
+ lessopen++;
+ returnfd = 2;
+ }
#endif
}
if (*lessopen == '-') {
@@ -879,17 +888,32 @@ open_altfile(filename, pf, pfd)
*/
f = fileno(fd);
SET_BINARY(f);
+ *pfd = (void *) fd;
+ *pf = f;
if (read(f, &c, 1) != 1)
{
/*
- * Pipe is empty. This means there is no alt file.
+ * Error or pipe is empty. Close it and eventually
+ * check exit status of the pipe process.
*/
- pclose(fd);
+ if (pclose(fd) == 0 && returnfd == 2) {
+ /*
+ * Exit status was zero, so the EOF was correct
+ * empty output. Let the program open /dev/null
+ * instead, as the pipe is already closed.
+ * Set force_open to omit bad_file() check
+ * failure, as it is special 'c' pseudo-device.
+ */
+ *pf = 0;
+ *pfd = NULL;
+ force_open = 1;
+ return (save("/dev/null"));
+ }
+ *pf = 0;
+ *pfd = NULL;
return (NULL);
}
ch_ungetchar(c);
- *pfd = (void *) fd;
- *pf = f;
return (save("-"));
}
#endif
diff -rup less-436-orig/less.nro less-436/less.nro
--- less-436-orig/less.nro 2011-02-09 16:00:12.520936431 +0100
+++ less-436/less.nro 2011-02-09 16:30:33.161235986 +0100
@@ -1147,11 +1147,26 @@ lesspipe.sh:
.br
;;
.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
+The script should return zero if the output was valid and non-zero
+otherwise, so less could detect even a valid empty output
+(for example while uncompressing gzipped empty file).
+For backward-compatibility, this is not required by default. To turn
+this functionality there should be another vertical bar (|) straight
+after the first one in the LESSOPEN environment variable, eg.
+LESSOPEN="||lesspipe.sh %s".
+.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.