Applied patch from Dave Beckett to support "@filename" as a "--size" argument.

doc/ACKNOWLEDGEMENTS.md

@@ -74,6 +74,7 @@ is acknowledged and greatly appreciated:
  * Jakub Wilk <jwilk@jwilk.net> - corrected README encoding
  * [ikasty](https://github.com/ikasty) - added relative filename display to "`--watchfd`"
  * [Michael Weiß](https://github.com/quitschbo) - corrected behaviour when not attached to a terminal
- * [christoph-zededa](https://github.com/christoph-zededa) - provided OS X suppot for "`--watchfd`"
+ * [christoph-zededa](https://github.com/christoph-zededa) - provided OS X support for "`--watchfd`"
+ * [Dave Beckett](https://github.com/dajobe)) - added "`@filename`" syntax to "`--size`"
 
 ---

doc/NEWS.md

@@ -1,8 +1,9 @@
 UNRELEASED
  * dropped: support for Red Hat Enterprise Linux and its derivatives has been dropped; removed the RPM spec file, and will no longer build binaries
  * fix: correction to `pv_in_foreground()` to behave as its comment block says it should, when not on a terminal - corrects [GH#19 "No output in Arch Linux initcpio after 1.6.6"](https://github.com/a-j-wood/pv/issues/19), [GH#55 "pv Stopped Working in the Background"](https://github.com/a-j-wood/pv/issues/55) (pull request [#64](https://github.com/a-j-wood/pv/pull/64) supplied by [Michael Weiß](https://github.com/quitschbo))
- * feature: the "`--watchfd`" option will now show relative filenames, if they are under the current directory (pull request [#66](https://github.com/a-j-wood/pv/pull/66) supplied by [ikasty](https://github.com/ikasty))
+ * feature: the "`--size`" option now accepts "`@filename`" to use the size of another file (pull request [#57](https://github.com/a-j-wood/pv/pull/57) supplied by [Dave Beckett](https://github.com/dajobe))
  * feature: the "`--watchfd`" option is now available on OS X (pull request [#60](https://github.com/a-j-wood/pv/pull/60) supplied by [christoph-zededa](https://github.com/christoph-zededa))
+ * feature: the "`--watchfd`" option will now show relative filenames, if they are under the current directory (pull request [#66](https://github.com/a-j-wood/pv/pull/66) supplied by [ikasty](https://github.com/ikasty))
  * docs: moved all open issues into GitHub and updated the TODO list
  * docs: renamed README to README.md and altered it to Markdown format
  * docs: moved contributors from the README to docs/ACKNOWLEDGEMENTS.md

doc/quickref.1.in

@@ -243,7 +243,18 @@ etc can be used as with
 .BR -L .
 .TP
 .B ""
-Has no effect if used with
+If
+.B SIZE
+starts with
+.BR "@" ,
+the size of file whose name follows the
+.B @
+will be used.
+.TP
+.B ""
+Note that
+.B \-\-size
+has no effect if used with
 .B -d PID
 to watch all file descriptors of a process, but will work with
 .BR "-d PID:FD" .

src/main/options.c

@@ -8,11 +8,13 @@
 #include "options.h"
 #include "library/getopt.h"
 #include "pv.h"
+#include "pv-internal.h"
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
+#include <sys/stat.h>
 #include <unistd.h>
 
 
@@ -138,6 +140,9 @@ opts_t opts_parse(int argc, char **argv)
 		 */
 		switch (c) {
 		case 's':
+			/* "-s @" is valid, so allow it. */
+			if ('@' == *optarg)
+				break;
 		case 'A':
 		case 'w':
 		case 'H':
@@ -257,7 +262,28 @@ opts_t opts_parse(int argc, char **argv)
 			opts->delay_start = pv_getnum_d(optarg);
 			break;
 		case 's':
-			opts->size = pv_getnum_ull(optarg);
+			/* Permit "@<filename>" as well as just a number. */
+			if ('@' == *optarg) {
+				const char *size_file = 1 + optarg;
+				struct stat64 sb;
+				int rc;
+
+				rc = 0;
+				memset(&sb, 0, sizeof(sb));
+				rc = stat64(size_file, &sb);
+				if (0 == rc) {
+					opts->size = sb.st_size;
+				} else {
+					fprintf(stderr, "%s: %s %s: %s\n",
+						opts->program_name,
+						_("failed to stat file"),
+						size_file, strerror(errno));
+					opts_free(opts);
+					return NULL;
+				}
+			} else {
+				opts->size = pv_getnum_ull(optarg);
+			}
 			break;
 		case 'l':
 			opts->linemode = true;