lslogins: add -H and --list-columns option; declutter --help output

This moves the list of available columns from the --help output
to the '--list-columns' option and makes the usage information
more readable.

Signed-off-by: Christian Goeschel Ndjomouo <cgoesc2@wgu.edu>

diff --git a/login-utils/lslogins.c b/login-utils/lslogins.c
index 8c732d600d43a47b215fbd202ee5d4ed917212b3..90db60cbc890dd001a5df6534bb4d0a85b78f8cd 100644 (file)
--- a/login-utils/lslogins.c
+++ b/login-utils/lslogins.c
@@ -63,6 +63,7 @@
 #include "logindefs.h"
 #include "procfs.h"
 #include "timeutils.h"
+#include "column-list-table.h"
 
 /* Types used for JSON and --list-columns */
 enum {
@@ -1549,7 +1550,6 @@ static int parse_time_mode(const char *s)
 static void __attribute__((__noreturn__)) usage(void)
 {
        FILE *out = stdout;
-       size_t i;
 
        fputs(USAGE_HEADER, out);
        fprintf(out, _(" %s [options] [<username>]\n"), program_invocation_short_name);
@@ -1587,20 +1587,39 @@ static void __attribute__((__noreturn__)) usage(void)
        fputs(_("     --lastlog2 <path>    set an alternate path for lastlog2\n"), out);
 #endif
        fputs(USAGE_SEPARATOR, out);
+       /* FIXME: Replace with USAGE_LIST_COLUMNS_OPTION() macro from include/c.h */
+       fputs(_(" -H, --list-columns       list the available columns\n"), out);
        fprintf(out, USAGE_HELP_OPTIONS(26));
 
-       fputs(USAGE_COLUMNS, out);
-       for (i = 0; i < ARRAY_SIZE(coldescs); i++)
-               fprintf(out, " %14s  %s\n", coldescs[i].name, _(coldescs[i].help));
-
        fprintf(out, USAGE_MAN_TAIL("lslogins(1)"));
 
        exit(EXIT_SUCCESS);
 }
 
+static void __attribute__((__noreturn__)) list_columns(void)
+{
+       size_t i;
+       struct libscols_table *tbl = xcolumn_list_table_new("lslogins-columns", stdout,
+                                               outmode == OUT_RAW ? 1 : 0,
+                                               outmode == OUT_JSON ? 1 : 0);
+
+       for (i = 0; i < ARRAY_SIZE(coldescs); i++) {
+               const struct lslogins_coldesc *ci = &coldescs[i];
+
+               xcolumn_list_table_append_line(tbl, ci->name,
+                       ci->type == COLTYPE_NUM  ? SCOLS_JSON_NUMBER : SCOLS_JSON_STRING,
+                       NULL, _(ci->help));
+       }
+
+       scols_print_table(tbl);
+       scols_unref_table(tbl);
+
+       exit(EXIT_SUCCESS);
+}
+
 int main(int argc, char *argv[])
 {
-       int c;
+       int c, collist = 0;
        char *logins = NULL, *groups = NULL, *outarg = NULL;
        char *path_lastlog = _PATH_LASTLOG, *path_wtmp = _PATH_WTMP, *path_btmp = _PATH_BTMP;
        struct lslogins_control *ctl = xcalloc(1, sizeof(struct lslogins_control));
@@ -1644,6 +1663,7 @@ int main(int argc, char *argv[])
                { "version",        no_argument,        0, 'V' },
                { "pwd",            no_argument,        0, 'p' },
                { "print0",         no_argument,        0, 'z' },
+               { "list-columns",   no_argument,        0, 'H' },
                { "wtmp-file",      required_argument,  0, OPT_WTMP },
                { "btmp-file",      required_argument,  0, OPT_BTMP },
                { "lastlog-file",   required_argument,  0, OPT_LASTLOG },
@@ -1678,7 +1698,7 @@ int main(int argc, char *argv[])
        add_column(columns, ncolumns++, COL_UID);
        add_column(columns, ncolumns++, COL_USER);
 
-       while ((c = getopt_long(argc, argv, "acefGg:hJLl:no:prsuVyzZ",
+       while ((c = getopt_long(argc, argv, "acefGg:HhJLl:no:prsuVyzZ",
                                longopts, NULL)) != -1) {
 
                err_exclusive_options(c, longopts, excl, excl_st);
@@ -1763,6 +1783,9 @@ int main(int argc, char *argv[])
                case 'z':
                        outmode = OUT_NUL;
                        break;
+               case 'H':
+                       collist = 1;
+                       break;
                case OPT_LASTLOG:
                        path_lastlog = optarg;
                        break;
@@ -1813,6 +1836,9 @@ int main(int argc, char *argv[])
                }
        }
 
+       if (collist)
+               list_columns();
+
        if (argc - optind == 1) {
                if (strchr(argv[optind], ','))
                        errx(EXIT_FAILURE, _("Only one user may be specified. Use -l for multiple users."));