Turns out, making strings shell-proof is harder than expected:
# machinectl set-hostname foo|poweroff . /etc/machine-info
(This could be simplified by quoting *and* escaping all characters,
which is harmless in shell but unnecessary.)
---
src/shared/fileio.c | 4 ++--
src/shared/util.h | 6 ++
2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/src/shared/fileio.c b/src/shared/fileio.c
index b0ab780..cbb40c2 100644
--- a/src/shared/fileio.c
+++ b/src/shared/fileio.c
@@ -738,11 +738,11 @@ static void write_env_var(FILE *f, const char *v) {
p++;
fwrite(v, 1, p-v, f);
-if (string_has_cc(p, NULL) || chars_intersect(p, WHITESPACE
\'\\\`$)) {
+if (string_has_cc(p, NULL) || chars_intersect(p, WHITESPACE
SHELL_NEED_QUOTES)) {
fputc('\', f);
for (; *p; p++) {
-if (strchr(\'\\\`$, *p))
+if (strchr(SHELL_NEED_ESCAPE, *p))
fputc('\\', f);
fputc(*p, f);
diff --git a/src/shared/util.h b/src/shared/util.h
index c5eadc9..b3187a9 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -93,6 +93,12 @@
#define COMMENTS #;
#define GLOB_CHARS *?[
+/* What characters are special in the shell? */
+/* must be escaped outside and inside double-quotes */
+#define SHELL_NEED_ESCAPE \\\`$
+/* can be escaped or double-quoted */
+#define SHELL_NEED_QUOTES SHELL_NEED_ESCAPE GLOB_CHARS '()|;
+
#define FORMAT_BYTES_MAX 8
#define ANSI_HIGHLIGHT_ON \x1B[1;39m
--
2.0.1
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