column: support negative numbers in range

Fixes: https://github.com/util-linux/util-linux/issues/1700
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/text-utils/column.c b/text-utils/column.c
index 0a891117cc6f60b910e45639156b009e17b72393..a443ab8b1d46f31ad9ef02cf435586d4e2837bd9 100644 (file)
--- a/text-utils/column.c
+++ b/text-utils/column.c
@@ -251,23 +251,27 @@ static void init_table(struct column_control *ctl)
 
 }
 
-static struct libscols_column *get_last_visible_column(struct column_control *ctl)
+static struct libscols_column *get_last_visible_column(struct column_control *ctl, int n)
 {
        struct libscols_iter *itr;
-       struct libscols_column *cl, *last = NULL;
+       struct libscols_column *cl, *res = NULL;
 
-       itr = scols_new_iter(SCOLS_ITER_FORWARD);
+       itr = scols_new_iter(SCOLS_ITER_BACKWARD);
        if (!itr)
                err_oom();
 
        while (scols_table_next_column(ctl->tab, itr, &cl) == 0) {
                if (scols_column_get_flags(cl) & SCOLS_FL_HIDDEN)
                        continue;
-               last = cl;
+               if (n == 0) {
+                       res = cl;
+                       break;
+               }
+               n--;
        }
 
        scols_free_iter(itr);
-       return last;
+       return res;
 }
 
 static struct libscols_column *string_to_column(struct column_control *ctl, const char *str)
@@ -279,7 +283,7 @@ static struct libscols_column *string_to_column(struct column_control *ctl, cons
 
                cl = scols_table_get_column(ctl->tab, n);
        } else if (strcmp(str, "-1") == 0)
-               cl = get_last_visible_column(ctl);
+               cl = get_last_visible_column(ctl, 0);
        else
                cl = scols_table_get_column_by_name(ctl->tab, str);
 
@@ -358,7 +362,10 @@ static void apply_columnflag_from_list(struct column_control *ctl, const char *l
                /* parse range (N-M) */
                if (strchr(*one, '-') && parse_range(*one, &low, &up, 0) == 0) {
                        for (; low <= up; low++) {
-                               cl = scols_table_get_column(ctl->tab, low-1);
+                               if (low < 0)
+                                       cl = get_last_visible_column(ctl, (low * -1) -1);
+                               else
+                                       cl = scols_table_get_column(ctl->tab, low-1);
                                if (cl)
                                        column_set_flag(cl, flag);
                        }
@@ -490,7 +497,7 @@ static void modify_table(struct column_control *ctl)
                                SCOLS_FL_WRAP , _("failed to parse --table-wrap list"));
 
        if (!ctl->tab_colnoextrem) {
-               struct libscols_column *cl = get_last_visible_column(ctl);
+               struct libscols_column *cl = get_last_visible_column(ctl, 0);
                if (cl)
                        column_set_flag(cl, SCOLS_FL_NOEXTREMES);
        }