lib/strutils: add ul_strchr_escaped()

Like strchr(), but ignores escaped chars.

Signed-off-by: Karel Zak <kzak@redhat.com>

include/strutils.h

@@ -389,6 +389,8 @@ extern int strappend(char **a, const char *b);
 
 extern const char *split(const char **state, size_t *l, const char *separator, int quoted);
 
+extern char *ul_strchr_escaped(const char *s, int c);
+
 extern int skip_fline(FILE *fp);
 extern int ul_stralnumcmp(const char *p1, const char *p2);
 

lib/strutils.c

@@ -998,6 +998,37 @@ static size_t strcspn_escaped(const char *s, const char *reject)
         return n - escaped;
 }
 
+/*
+ * Like strchr() but ignores @c if escaped by '\', '\\' is interpreted like '\'.
+ *
+ * For example for @c='X':
+ *
+ *      "abcdXefgXh"    --> "XefgXh"
+ *	"abcd\XefgXh"   --> "Xh"
+ *	"abcd\\XefgXh"  --> "XefgXh"
+ *	"abcd\\\XefgXh" --> "Xh"
+ *	"abcd\Xefg\Xh"  --> (null)
+ *
+ *	"abcd\\XefgXh"  --> "\XefgXh"   for @c='\\'
+ */
+char *ul_strchr_escaped(const char *s, int c)
+{
+	char *p;
+	int esc = 0;
+
+	for (p = (char *) s; p && *p; p++) {
+		if (!esc && *p == '\\') {
+			esc = 1;
+			continue;
+		}
+		if (*p == c && (!esc || c == '\\'))
+			return p;
+		esc = 0;
+	}
+
+	return NULL;
+}
+
 /* Split a string into words. */
 const char *split(const char **state, size_t *l, const char *separator, int quoted)
 {
@@ -1295,6 +1326,10 @@ int main(int argc, char *argv[])
 		printf("'%s'-->%hu\n", argv[2], strtou16_or_err(argv[2], "strtou16 failed"));
 		return EXIT_SUCCESS;
 
+	} else if (argc == 4 && strcmp(argv[1], "--strchr-escaped") == 0) {
+		printf("\"%s\" --> \"%s\"\n", argv[2], ul_strchr_escaped(argv[2], *argv[3]));
+		return EXIT_SUCCESS;
+
 	} else {
 		fprintf(stderr, "usage: %1$s --size <number>[suffix]\n"
 				"       %1$s --cmp-paths <path> <path>\n"