From 287fc41c1c884edd9bceca94f73fc38ad49d253b Mon Sep 17 00:00:00 2001
From: Ole Tange <ole@tange.dk>
Date: Fri, 2 Jan 2015 11:33:40 +0100
Subject: [PATCH] sem: --shebang-wrap example in manual.

---
 src/parallel     |  2 +-
 src/parallel.pod | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/parallel b/src/parallel
index 9399337e..f818fb26 100755
--- a/src/parallel
+++ b/src/parallel
@@ -955,7 +955,7 @@ sub parse_options {
 
 sub init_globals {
     # Defaults:
-    $Global::version = 20141229;
+    $Global::version = 20150101;
     $Global::progname = 'parallel';
     $Global::infinity = 2**31;
     $Global::debug = 0;
diff --git a/src/parallel.pod b/src/parallel.pod
index b4234fed..b981dcb5 100644
--- a/src/parallel.pod
+++ b/src/parallel.pod
@@ -1534,6 +1534,9 @@ On FreeBSD B<env> is needed:
   debian.org
   freenetproject.org
 
+There are many limitations of shebang (#!) depending on your operating
+system. See details on http://www.in-ulm.de/~mascheck/various/shebang/
+
 
 =item B<--shebang-wrap>
 
@@ -3010,6 +3013,37 @@ same time:
   seq 3 | parallel sem --id mymutex sed -i -e 'i{}' myfile
 
 
+=head1 EXAMPLE: Mutex for a script
+
+Assume a script is called from cron or from a web service, but only
+one instance can be run at a time. With B<sem> and B<--shebang-wrap>
+the script can be made to wait for other instances to finish. Here in
+B<bash>:
+
+  #!/usr/bin/sem --shebang-wrap -u --id $0 --fg /bin/bash
+  
+  echo This will run
+  sleep 5
+  echo exclusively
+
+Here B<perl>:
+
+  #!/usr/bin/sem --shebang-wrap -u --id $0 --fg /usr/bin/perl
+  
+  print "This will run ";
+  sleep 5;
+  print "exclusively\n";
+
+Here B<python>:
+
+  #!/usr/local/bin/sem --shebang-wrap -u --id $0 --fg /usr/bin/python
+  
+  import time
+  print "This will run ";
+  time.sleep(5)
+  print "exclusively";
+
+
 =head1 EXAMPLE: Start editor with filenames from stdin (standard input)
 
 You can use GNU B<parallel> to start interactive programs like emacs or vi: