The change in behavior can be seen with the invocations below:
$ time ./src/groups-prev $(yes collin | head -n 10000 | tr '\n' ' ') >&-
groups-prev: write error: Bad file descriptor
real 0m35.295s
user 0m9.271s
sys 0m17.325s
$ time ./src/groups $(yes collin | head -n 10000 | tr '\n' ' ') >&-
groups: write error: Bad file descriptor
real 0m0.021s
user 0m0.006s
sys 0m0.018s
-- 8< --
* NEWS: Mention the improvement.
* src/groups.c (main): Call fflush for each listed user to check for
write errors.
---
NEWS | 3 +++
src/groups.c | 3 +++
2 files changed, 6 insertions(+)
diff --git a/NEWS b/NEWS
index cf1b1414e..13bb6031a 100644
--- a/NEWS
+++ b/NEWS
@@ -18,6 +18,9 @@ GNU coreutils NEWS -*-
outline -*-
** Improvements
+ 'group' will now exit immediately upon receiving a write error, which is
+ significant when listing information for many users.
+
'nl' now supports multi-byte --section-delimiter characters.
'shuf -i' now operates up to two times faster on systems with unlocked stdio
diff --git a/src/groups.c b/src/groups.c
index faed5c810..3daf410d9 100644
--- a/src/groups.c
+++ b/src/groups.c
@@ -134,6 +134,9 @@ main (int argc, char **argv)
if (!print_group_list (argv[optind], ruid, rgid, egid, true, ' '))
ok = false;
putchar ('\n');
+
+ if (fflush (stdout) < 0)
+ write_error ();
}
}
--
2.53.0
