From 011a56846f5b66db667e7fbec06ffcc11cd96eed Mon Sep 17 00:00:00 2001
From: Alexandre Duret-Lutz <adl@lrde.epita.fr>
Date: Mon, 11 May 2015 19:53:41 +0200
Subject: [PATCH] org: document -0

* doc/org/ioltl.org: Add an example with xargs -0.
* src/bin/common_aoutput.hh (statistics): Do not print nullptr if %F is
empty.
---
 doc/org/ioltl.org         | 34 ++++++++++++++++++++++++++++++----
 src/bin/common_aoutput.hh |  2 +-
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/doc/org/ioltl.org b/doc/org/ioltl.org
index 78cd19b45..da0f3471f 100644
--- a/doc/org/ioltl.org
+++ b/doc/org/ioltl.org
@@ -146,13 +146,12 @@ used by [[http://www.ltl2dstar.de][ltl2dstar]].
 All tools that output LTL/PSL formulas implement the following options:
 
 #+BEGIN_SRC sh :results verbatim :exports results
-ltlfilt --help | sed -n '/Output options:/,/^$/p' | sed '1d;$d'
+genltl --help | sed -n '/Output options:/,/^$/p' | sed '1d;$d'
 #+END_SRC
 #+RESULTS:
 #+begin_example
-  -c, --count                print only a count of matched formulas
-  -n, --max-count=NUM        output at most NUM formulas
-  -q, --quiet                suppress all normal output
+  -0, --zero-terminated-output   separate output formulas with \0 instead of \n
+                             (for use with xargs -0)
   -8, --utf8                 output using UTF-8 characters
       --csv-escape           quote the formula for use in a CSV file
       --format=FORMAT        specify how each line should be output (default:
@@ -231,6 +230,33 @@ rm -f example-*.ltl
 #+END_SRC
 #+RESULTS:
 
+Option =-0= is useful if the list of formulas is passed to =xargs=.
+=xargs= normally splits its input on white space (which are frequent
+in LTL formulas), but you can use =xargs -0= to split the input on
+null characters.   So for instance the following two invocations have
+nearly the same output:
+
+#+BEGIN_SRC sh :results verbatim :exports both
+genltl -0 --gh-q=1..4 | xargs -0 ltl2tgba --stats='%F,%f,%s'
+genltl --gh-q=1..4 | ltl2tgba -F- --stats='%F,%f,%s'
+#+END_SRC
+
+#+RESULTS:
+: ,Fp1 | Gp2,3
+: ,(Fp1 | Gp2) & (Fp2 | Gp3),8
+: ,(Fp1 | Gp2) & (Fp2 | Gp3) & (Fp3 | Gp4),18
+: ,(Fp1 | Gp2) & (Fp2 | Gp3) & (Fp3 | Gp4) & (Fp4 | Gp5),42
+: -,Fp1 | Gp2,3
+: -,(Fp1 | Gp2) & (Fp2 | Gp3),8
+: -,(Fp1 | Gp2) & (Fp2 | Gp3) & (Fp3 | Gp4),18
+: -,(Fp1 | Gp2) & (Fp2 | Gp3) & (Fp3 | Gp4) & (Fp4 | Gp5),42
+
+The only difference is that for the first command, =ltl2tgba= received
+its formulas from the command-line arguments supplied by =xargs= (so
+=%F= is empty as there is no input file), while in the second case the
+formula where read from standard input (denoted by =-=).
+
+
 
 #  LocalWords:  lbt LBT's filename UTF gfa GFa ltlfilt LBTT scheck
 #  LocalWords:  utf associativity
diff --git a/src/bin/common_aoutput.hh b/src/bin/common_aoutput.hh
index 4f94bc320..a43f609e8 100644
--- a/src/bin/common_aoutput.hh
+++ b/src/bin/common_aoutput.hh
@@ -111,7 +111,7 @@ public:
 	const spot::ltl::formula* f,
 	const char* filename, int loc, double run_time)
   {
-    filename_ = filename;
+    filename_ = filename ? filename : "";
     if (loc >= 0 && has('L'))
       {
 	std::ostringstream os;