From 8c343e89c792d0e55f1137d44a5ac08eab6b1084 Mon Sep 17 00:00:00 2001
From: Consolatis <35009135+Consolatis@users.noreply.github.com>
Date: Wed, 13 Sep 2023 15:25:05 +0200
Subject: [PATCH] actions: Prevent env var expansion for subshells like `$()`

We currently expand Execute action commands like
`sh -c 'echo $(date) >> /tmp/foo'` to
`sh -c 'echo (date) >> /tmp/foo'`

This obviously breaks the subshell. This patch fixes it
by preventing single `$` being replaced with nothing.
---
 src/common/buf.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/common/buf.c b/src/common/buf.c
index 740489dd..45adf72e 100644
--- a/src/common/buf.c
+++ b/src/common/buf.c
@@ -33,6 +33,13 @@ buf_expand_shell_variables(struct buf *s)
 				++p;
 			}
 			*p = '\0';
+
+			/* Don't expand single $ (as used by subshells) */
+			if (!strlen(environment_variable.buf)) {
+				buf_add(&new, "$");
+				continue;
+			}
+
 			i += strlen(environment_variable.buf);
 			strip_curly_braces(environment_variable.buf);
 			p = getenv(environment_variable.buf);