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authorDenys Vlasenko <vda.linux@googlemail.com>2010-05-20 19:46:45 (GMT)
committer Denys Vlasenko <vda.linux@googlemail.com>2010-05-20 19:46:45 (GMT)
commit53b513331add89e83c1327579f3da91ebbe97570 (patch)
tree766859b51744af5b705bf785c95ff597feb9cd1c
parentee0775dd13a84316f6fd49c930237e6dec241dba (diff)
downloadbusybox-53b513331add89e83c1327579f3da91ebbe97570.tar.gz
busybox-53b513331add89e83c1327579f3da91ebbe97570.tar.bz2
hush: explain various parameter expansion ops in comments
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--shell/hush.c44
1 files changed, 36 insertions, 8 deletions
diff --git a/shell/hush.c b/shell/hush.c
index d5cea07..06e9af2 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -2614,8 +2614,16 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
debug_printf_expand("%s\n", val);
} else if (exp_op) {
if (exp_op == '%' || exp_op == '#') {
+ /* Standard-mandated substring removal ops:
+ * ${parameter%word} - remove smallest suffix pattern
+ * ${parameter%%word} - remove largest suffix pattern
+ * ${parameter#word} - remove smallest prefix pattern
+ * ${parameter##word} - remove largest prefix pattern
+ *
+ * Word is expanded to produce a glob pattern.
+ * Then var's value is matched to it and matching part removed.
+ */
if (val) {
- /* we need to do a pattern match */
bool match_at_left;
char *loc;
scan_t scan = pick_scan(exp_op, *exp_word, &match_at_left);
@@ -2629,18 +2637,38 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
*loc = '\0';
}
} else { /* one of :-=+? */
+//TODO: check validity of exp_op. Currently it can be anything.
//TODO: handle ${VAR:N[:M]} here. N, M can be expressions similar to $((EXPR)): 2+2, 2+var etc
- /* we need to do an expansion */
- int exp_test = (!val || ((exp_save == ':') && !val[0]));
+ /* Standard-mandated substitution ops:
+ * ${var?word} - indicate error if unset
+ * If var is unset, word (or a message indicating it is unset
+ * if word is null) is written to standard error
+ * and the shell exits with a non-zero exit status.
+ * Otherwise, the value of var is substituted.
+ * ${var-word} - use default value
+ * If var is unset, word is substituted.
+ * ${var=word} - assign and use default value
+ * If var is unset, word is assigned to var.
+ * In all cases, final value of var is substituted.
+ * ${var+word} - use alternative value
+ * If var is unset, null is substituted.
+ * Otherwise, word is substituted.
+ *
+ * Word is subjected to tilde expansion, parameter expansion,
+ * command substitution, and arithmetic expansion.
+ * If word is not needed, it is not expanded.
+ *
+ * Colon forms (${var:-word}, ${var:=word} etc) do the same,
+ * but also treat null var as if it is unset.
+ */
+ int use_word = (!val || ((exp_save == ':') && !val[0]));
if (exp_op == '+')
- exp_test = !exp_test;
+ use_word = !use_word;
debug_printf_expand("expand: op:%c (null:%s) test:%i\n", exp_op,
- (exp_save == ':') ? "true" : "false", exp_test);
- if (exp_test) {
+ (exp_save == ':') ? "true" : "false", use_word);
+ if (use_word) {
if (exp_op == '?') {
//TODO: how interactive bash aborts expansion mid-command?
- /* ${var?[error_msg_if_unset]} */
- /* ${var:?[error_msg_if_unset_or_null]} */
/* mimic bash message */
die_if_script("%s: %s",
var,