+ for (; *argv != NULL; argv++)
is argv[1] guaranteed? I have never seen this before.
On Wed, Jan 26, 2022 at 9:52 PM Scott Cheloha <scottchel...@gmail.com>
wrote:
> The main loop in head(1) is obfuscated. In particular, the path
> through the loop to exit(3) is extremely clever. Clever in a bad way.
>
> This patch moves the open/read/write/close portions of the loop out
> into a separate function, head_file(). I think the result is easier
> to understand. We only loop in main() if we have file arguments, the
> argv[] loop is idiomatic and simple, we actually reach the end of
> main(), etc.
>
> In a subsequent patch I intend to switch to getline(3) and add more
> error checking to head_file(). For now I have just moved the
> getc/putchar loop into head_file() as-is.
>
> ok?
>
> Index: head.c
> ===================================================================
> RCS file: /cvs/src/usr.bin/head/head.c,v
> retrieving revision 1.22
> diff -u -p -r1.22 head.c
> --- head.c 10 Oct 2021 15:57:25 -0000 1.22
> +++ head.c 27 Jan 2022 04:41:09 -0000
> @@ -37,6 +37,7 @@
> #include <errno.h>
> #include <unistd.h>
>
> +int head_file(const char *, long, int);
> static void usage(void);
>
> /*
> @@ -49,9 +50,7 @@ int
> main(int argc, char *argv[])
> {
> const char *errstr;
> - FILE *fp;
> - long cnt;
> - int ch, firsttime;
> + int ch;
> long linecnt = 10;
> int status = 0;
>
> @@ -81,33 +80,46 @@ main(int argc, char *argv[])
> }
> argc -= optind, argv += optind;
>
> - for (firsttime = 1; ; firsttime = 0) {
> - if (!*argv) {
> - if (!firsttime)
> - exit(status);
> - fp = stdin;
> - if (pledge("stdio", NULL) == -1)
> - err(1, "pledge");
> - } else {
> - if ((fp = fopen(*argv, "r")) == NULL) {
> - warn("%s", *argv++);
> - status = 1;
> - continue;
> - }
> - if (argc > 1) {
> - if (!firsttime)
> - putchar('\n');
> - printf("==> %s <==\n", *argv);
> - }
> - ++argv;
> - }
> - for (cnt = linecnt; cnt && !feof(fp); --cnt)
> - while ((ch = getc(fp)) != EOF)
> - if (putchar(ch) == '\n')
> - break;
> - fclose(fp);
> + if (argc == 0) {
> + if (pledge("stdio", NULL) == -1)
> + err(1, "pledge");
> +
> + status = head_file(NULL, linecnt, 0);
> + } else {
> + for (; *argv != NULL; argv++)
> + status |= head_file(*argv, linecnt, argc > 1);
> }
> - /*NOTREACHED*/
> +
> + return status;
> +}
> +
> +int
> +head_file(const char *path, long count, int need_header)
> +{
> + FILE *fp;
> + int ch;
> + static int first = 1;
> +
> + if (path != NULL) {
> + fp = fopen(path, "r");
> + if (fp == NULL) {
> + warn("%s", path);
> + return 1;
> + }
> + if (need_header) {
> + printf("%s==> %s <==\n", first ? "" : "\n", path);
> + first = 0;
> + }
> + } else
> + fp = stdin;
> +
> + for (; count > 0 && !feof(fp); --count)
> + while ((ch = getc(fp)) != EOF)
> + if (putchar(ch) == '\n')
> + break;
> + fclose(fp);
> +
> + return 0;
> }
>
>
>
>
