xe: revise logic to only read new arguments when we immediately need them

This changes behavior on pipes that are written slowly, else there is a
one-line delay between executions.

1 files changed, 7 insertions, 1 deletions

diff --git a/tests b/tests
index 2e92b79..07b68e1 100755
--- a/tests
+++ b/tests
@@ -1,5 +1,5 @@
 #!/bin/sh
-printf '1..43\n'
+printf '1..44\n'
 
 set -e
 
@@ -175,6 +175,12 @@ check_output 'with ITER' '$XE -a -s "echo \$ITER" -- a b c' <<EOF
 3
 EOF
 
+check_output 'is eager' '{ echo 1; sleep 1; echo 11 >/dev/stderr; echo 2; } | xe echo' <<EOF
+1
+11
+2
+EOF
+
 printf '# error handling\n'
 
 check_output 'exit code on success' 'true | $XE; echo $?' <<EOF