Ignore logfile's name that begins with the "-" symbol

This fixes 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.

Signed-off-by: Alexander Naumov <alexander_naumov@opensuse.org>

3 files changed, 6 insertions, 4 deletions

diff --git a/src/doc/screen.1 b/src/doc/screen.1
index 23b4d7b..eabd763 100644
--- a/src/doc/screen.1
+++ b/src/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/src/doc/screen.texinfo b/src/doc/screen.texinfo
index 2ff39b0..c94993e 100644
--- a/src/doc/screen.texinfo
+++ b/src/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/src/screen.c b/src/screen.c
index e7a6cd2..5cf23e1 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -670,7 +670,7 @@ int main(int ac, char** av)
             if (--ac != 0) {
               screenlogfile = SaveStr(*++av);
               if (screenlogfile[0] == '-')
-                Panic(0, "-L: logfile name can not start with \"-\" symbol");
+                screenlogfile = SaveStr("screenlog.%n");
               if (strlen(screenlogfile) > PATH_MAX)
                 Panic(0, "-L: logfile name too long. (max. %d char)", PATH_MAX);