hush: Add default value substitution support

Use standard sh syntax:
${VAR:-default}
	Use default value: if VAR is set and non-null, expands to $VAR.
	Otherwise, expands to default.
${VAR:=default}
	Set default value: if VAR is set and non-null, expands to $VAR.
	Otherwise, sets hush VAR to default and expands to default.
${VAR:+default}
	If VAR is set and non-null, expands to the empty string.
	Otherwise, expands to default.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>

diff --git a/common/hush.c b/common/hush.c
index 1eff182efaf23599af42d0ddd3fb06af16ba1a2d..39cf203a9fc7849ad5ace771b17006e40a2d9c5c 100644 (file)
--- a/common/hush.c
+++ b/common/hush.c
@@ -2743,13 +2743,50 @@ static int parse_group(o_string *dest, struct p_context *ctx,
 static char *lookup_param(char *src)
 {
        char *p;
+       char *sep;
+       char *default_val = NULL;
+       int assign = 0;
+       int expand_empty = 0;
 
        if (!src)
                return NULL;
 
-               p = getenv(src);
-               if (!p)
-                       p = get_local_var(src);
+       sep = strchr(src, ':');
+
+       if (sep) {
+               *sep = '\0';
+               if (*(sep + 1) == '-')
+                       default_val = sep+2;
+               if (*(sep + 1) == '=') {
+                       default_val = sep+2;
+                       assign = 1;
+               }
+               if (*(sep + 1) == '+') {
+                       default_val = sep+2;
+                       expand_empty = 1;
+               }
+       }
+
+       p = getenv(src);
+       if (!p)
+               p = get_local_var(src);
+
+       if (!p || strlen(p) == 0) {
+               p = default_val;
+               if (assign) {
+                       char *var = malloc(strlen(src)+strlen(default_val)+2);
+                       if (var) {
+                               sprintf(var, "%s=%s", src, default_val);
+                               set_local_var(var, 0);
+                       }
+                       free(var);
+               }
+       } else if (expand_empty) {
+               p += strlen(p);
+       }
+
+       if (sep)
+               *sep = ':';
 
        return p;
 }