Date: Tue, 12 Mar 2013 17:52:06 GMT From: Ilya Bakulin <ilya@bakulin.de> To: freebsd-gnats-submit@FreeBSD.org Subject: misc/176886: [PATCH] tail -F file1 file2 > file3 places filenames in file3 incorrectly Message-ID: <201303121752.r2CHq6l9016813@red.freebsd.org> Resent-Message-ID: <201303121800.r2CI01OX045024@freefall.freebsd.org>
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>Number: 176886
>Category: misc
>Synopsis: [PATCH] tail -F file1 file2 > file3 places filenames in file3 incorrectly
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Mar 12 18:00:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator: Ilya Bakulin
>Release: FreeBSD 9.0-RELEASE-p3 amd64
>Organization:
Deglitch Networks
>Environment:
uname -a
FreeBSD olymp.kibab.com 9.0-RELEASE-p3 FreeBSD 9.0-RELEASE-p3 #0: Tue Jun 12 02:52:29 UTC 2012 root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC amd64
>Description:
When using tail -F to watch several files and redirecting the output to file, the file name markers come _after_ the contents of the respective file, while when output is going directly to terminal everything is fine.
>How-To-Repeat:
[kibab@olymp ~/tmp]$ echo "File1_Content" > file1.txt
[kibab@olymp ~/tmp]$ echo "File2_Content" > file2.txt
[kibab@olymp ~/tmp]$ tail -F file1.txt file2.txt
==> file1.txt <==
File1_Content
==> file2.txt <==
File2_Content
^C
^^^ This is correct output. First we see filename marker for file1, then follows its content, then the same for file2.
[kibab@olymp ~/tmp]$ tail -F file1.txt file2.txt > file3.txt
^C
[kibab@olymp ~/tmp]$ cat file3.txt
File1_Content
==> file1.txt <==
File2_Content
==> file2.txt <==
^^^ This is wrong!
>Fix:
Attached patch solves the problem for me. It adds an explicit flush for stdout right after printing file name marker. What I don't understand is why it is not flushed by stdio automatically -- there is an '\n' at the end of the string being printf'ed...
After applying the patch the output looks correct:
[kibab@olymp ~/tmp]$ ~/repos/tail/tail -F file1.txt file2.txt > file3.txt
^C
[kibab@olymp ~/tmp]$ cat file3.txt
==> file1.txt <==
File1_Content
==> file2.txt <==
File2_Content
Patch attached with submission follows:
diff -ru /usr/src/usr.bin/tail/forward.c ./forward.c
--- /usr/src/usr.bin/tail/forward.c 2012-01-03 04:23:53.000000000 +0100
+++ ./forward.c 2013-03-12 18:18:22.000000000 +0100
@@ -319,8 +319,10 @@
if (file->fp) {
active = 1;
n++;
- if (no_files > 1 && !qflag)
+ if (no_files > 1 && !qflag) {
(void)printf("\n==> %s <==\n", file->file_name);
+ (void)fflush(stdout);
+ }
forward(file->fp, file->file_name, style, off, &file->st);
if (Fflag && fileno(file->fp) != STDIN_FILENO)
n++;
Only in .: forward.o
Only in .: misc.o
Only in .: read.o
Only in .: reverse.o
Only in .: tail
Only in .: tail.1.gz
Only in .: tail.o
>Release-Note:
>Audit-Trail:
>Unformatted:
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