Check for SRANDOM support in a safer manner

Given that the SRANDOM variable loses its special properties if unset,
to compare two expansions of it to one another ought to be more robust.
Do so up to three times, so as not to be foiled by the unlikely event of
the RNG repeating the same number.

Further, the prior check was defective because it incorrectly presumed
the minimum required version of bash to be 5.0 rather than 5.1.

Fixes: 5ee035a364bea8d12bc8abfe769014e230a212a6
Signed-off-by: Kerin Millar <kfm@plushkava.net>

1 files changed, 15 insertions, 1 deletions

diff --git a/functions.sh b/functions.sh
index 37ac8c2..a47bb2b 100644
--- a/functions.sh
+++ b/functions.sh
@@ -575,7 +575,20 @@ quote_args()
 srandom()
 {
 	# shellcheck disable=3028
-	if [ "${BASH_VERSINFO:-0}" -ge 5 ]; then
+	_has_srandom()
+	{
+		# The SRANDOM variable was introduced by bash 5.1. Check for at
+		# least 5.0, letting the alternate branch confirm its efficacy.
+		if [ "${BASH_VERSINFO-0}" -lt 5 ]; then
+			false
+		else
+			for _ in 1 2 3; do
+				test "${SRANDOM}" != "${SRANDOM}" && break
+			done
+		fi
+	}
+
+	if _has_srandom; then
 		srandom()
 		{
 			printf '%d\n' "$(( SRANDOM >> 1 ))"
@@ -625,6 +638,7 @@ srandom()
 		return 1
 	fi
 
+	unset -f _has_srandom
 	srandom
 }