ash: BASH_XTRACEFD bashism

Based on patch by Johannes Schindelin <johannes.schindelin@gmx.de>

function                                             old     new   delta
evalcommand                                         1447    1500     +53

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 2ad86c187..e80425f5e 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -188,6 +188,7 @@
 #define    BASH_PIPEFAIL        ENABLE_ASH_BASH_COMPAT
 #define    BASH_HOSTNAME_VAR    ENABLE_ASH_BASH_COMPAT
 #define    BASH_SHLVL_VAR       ENABLE_ASH_BASH_COMPAT
+#define    BASH_XTRACEFD        ENABLE_ASH_BASH_COMPAT
 
 #if defined(__ANDROID_API__) && __ANDROID_API__ <= 24
 /* Bionic at least up to version 24 has no glob() */
@@ -9792,6 +9793,15 @@ evalcommand(union node *cmd, int flags)
         expredir(cmd->ncmd.redirect);
         redir_stop = pushredir(cmd->ncmd.redirect);
         preverrout_fd = 2;
+        if (BASH_XTRACEFD && xflag) {
+                /* NB: bash closes fd == $BASH_XTRACEFD when it is changed.
+                 * we do not emulate this. We only use its value.
+                 */
+                const char *xtracefd = lookupvar("BASH_XTRACEFD");
+                if (xtracefd && is_number(xtracefd))
+                        preverrout_fd = atoi(xtracefd);
+
+        }
         status = redirectsafe(cmd->ncmd.redirect, REDIR_PUSH | REDIR_SAVEFD2);
 
         path = vpath.var_text;