Update \sys_shell_get:nnN return value (see #538)

latex3 · Feb 16, 2019 · 01e5777 · 01e5777
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diff --git a/l3kernel/CHANGELOG.md b/l3kernel/CHANGELOG.md
@@ -11,6 +11,10 @@ this project uses date-based 'snapshot' version identifiers.
 
 - `\str_log:n`, `\str_log:N`
 
+### Changed
+
+- Return values from `\sys_shell_get:nnN`
+
 ## [2019-02-15]
 
 ### Changed

diff --git a/l3kernel/l3candidates.dtx b/l3kernel/l3candidates.dtx
@@ -873,7 +873,7 @@
 %
 % \section{Additions to \pkg{l3sys}}
 %
-% \begin{function}[added = 2019-01-16]{\sys_shell_get:nnN}
+% \begin{function}[added = 2019-01-16, updated = 2019-02-16]{\sys_shell_get:nnN}
 % \begin{function}[TF,added = 2019-01-16]{\sys_shell_get:nnN}
 %   \begin{syntax}
 %     \cs{sys_shell_get:nnN} \Arg{shell~command} \Arg{setup} \meta{tl~var}
@@ -884,7 +884,8 @@
 %   \cs{tl_to_str:n}.  Category codes may need to be set appropriately
 %   via the \meta{setup} argument, which is run just before running the
 %   \meta{shell command} (in a group).
-%   If shell escape is disabled, the \meta{tl~var} will be empty.
+%   If shell escape is disabled, the \meta{tl~var} will be set to
+%   |\q_no_value| in the non-branching version.
 %   Note that quote characters (|"|) \emph{cannot} be used inside the
 %   \meta{shell command}.  The \cs{sys_shell_get:nnNTF} conditional
 %   returns \texttt{true} if the shell is available and no quote is
@@ -3045,7 +3046,7 @@
 \cs_new_protected:Npn \sys_shell_get:nnN #1#2#3
   {
     \sys_shell_get:nnNF {#1} {#2} #3
-      { \tl_clear:N #3 }
+      { \tl_set:Nn #3 { \q_no_value } }
   }
 \prg_new_protected_conditional:Npnn \sys_shell_get:nnN #1#2#3 { T , F , TF }
   {