From: Alexander Naumov <alexander_naumov@opensuse.org>
Date: Mon, 3 Jul 2017 10:48:05 +0200
Subject: [PATCH] Ignore logfile's name that begins with the "-" symbol

 This fixes the API:
 .
 To enable logging we use -L option. But in case of
 default logfile name (screenlog.0) we will need to
 define it anyway. Because screen will try to interpret
 next option as a parameter for -L option (which is
 logfile name). It will fails ALWAYS, because next
 parameter will always start with "-" symbol...
 what is not permited for logfile name of course.
 .
 For example:
 .
 $ screen -L -D -m ./configure
 .
 In this case logfile name is screenlog.0, because "-D"
 will not be interpreted by screen as a name of logfile.
Bug-Debian: https://bugs.debian.org/863095
Bug: https://savannah.gnu.org/bugs/?50440
Reviewd-By: Axel Beckert <abe@debian.org>
---
 doc/screen.1       | 4 ++--
 doc/screen.texinfo | 4 +++-
 screen.c           | 7 +++++--
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/doc/screen.1 b/doc/screen.1
index 0fe8d0e533c2..ee210346dab8 100644
--- a/doc/screen.1
+++ b/doc/screen.1
@@ -262,8 +262,8 @@ Ask your system administrator if you are not sure. Remove sessions with the
 tells
 .I screen
 to turn on automatic output logging for the windows. By default, logfile's name
-is screenlog.1. You can sets new name: add it right after -L option e.g. "screen
--L my_logfile".
+is screenlog.0. You can set new name: add it right after -L option e.g. "screen
+-L my_logfile". Keep in mind that name can not start with "-" symbol.
 .TP 5
 .B \-m
 causes
diff --git a/doc/screen.texinfo b/doc/screen.texinfo
index 2ff39b08a79c..c94993edd2ed 100644
--- a/doc/screen.texinfo
+++ b/doc/screen.texinfo
@@ -334,7 +334,9 @@ Remove sessions with the @samp{-wipe} option.
 
 @item -L
 Tell @code{screen} to turn on automatic output logging for the
-windows.
+windows. By default, logfile's name is screenlog.0. You can set new name:
+add it right after -L option e.g. "screen -L my_logfile". Keep in mind
+that name can not start with "-" symbol.
 
 @item -m
 Tell @code{screen} to ignore the @code{$STY} environment variable.  When
diff --git a/screen.c b/screen.c
index e60d0a712fb5..07f0c1387e32 100644
--- a/screen.c
+++ b/screen.c
@@ -669,8 +669,11 @@ int main(int ac, char** av)
           case 'L':
             if (--ac != 0) {
               screenlogfile = SaveStr(*++av);
-              if (screenlogfile[0] == '-')
-                Panic(0, "-L: logfile name can not start with \"-\" symbol");
+              if (screenlogfile[0] == '-') {
+                screenlogfile = SaveStr("screenlog.%n");
+                av--;
+                ac++;
+              }
               if (strlen(screenlogfile) > PATH_MAX)
                 Panic(0, "-L: logfile name too long. (max. %d char)", PATH_MAX);
             }