Save $PIPESTATUS for precmd and preexec functions to use. (#85)

Unfortunately, I couldn't figure out how to restore it for each
function, so I just made a copy in $BP_PIPESTATUS for those functions to
use.

For documentation of PIPESTATUS, see
https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html#index-PIPESTATUS

Closes #81.

Author: dseomn

bash-preexec.sh

@@ -39,8 +39,12 @@ fi
 __bp_imported="defined"
 
 # Should be available to each precmd and preexec
-# functions, should they want it.
+# functions, should they want it. $? and $_ are available as $? and $_, but
+# $PIPESTATUS is available only in a copy, $BP_PIPESTATUS.
+# TODO: Figure out how to restore PIPESTATUS before each precmd or preexec
+# function.
 __bp_last_ret_value="$?"
+BP_PIPESTATUS=("${PIPESTATUS[@]}")
 __bp_last_argument_prev_command="$_"
 
 __bp_inside_precmd=0
@@ -95,9 +99,9 @@ __bp_interactive_mode() {
 # This function is installed as part of the PROMPT_COMMAND.
 # It will invoke any functions defined in the precmd_functions array.
 __bp_precmd_invoke_cmd() {
-    # Save the returned value from our last command. Note: this MUST be the
-    # first thing done in this function.
-    __bp_last_ret_value="$?"
+    # Save the returned value from our last command, and from each process in
+    # its pipeline. Note: this MUST be the first thing done in this function.
+    __bp_last_ret_value="$?" BP_PIPESTATUS=("${PIPESTATUS[@]}")
 
     # Don't invoke precmds if we are inside an execution of an "original
     # prompt command" by another precmd execution loop. This avoids infinite

test/bash-preexec.bats

@@ -109,6 +109,22 @@ test_preexec_echo() {
     [[ "$output" == "251" ]]
 }
 
+@test "precmd should set \$BP_PIPESTATUS to the previous \$PIPESTATUS" {
+  echo_pipestatus() {
+    echo "${BP_PIPESTATUS[*]}"
+  }
+  # Helper function is necessary because Bats' run doesn't preserve $PIPESTATUS
+  set_pipestatus_and_run_precmd() {
+    false | true
+    __bp_precmd_invoke_cmd
+  }
+
+  precmd_functions+=(echo_pipestatus)
+  run 'set_pipestatus_and_run_precmd'
+  [[ $status == 0 ]]
+  [[ "$output" == "1 0" ]]
+}
+
 @test "precmd should set \$_ to be the previous last arg" {
     echo_last_arg() {
       echo "$_"