From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <73b6c42894bc770bc171ccc36e6bfe6a@vitanuova.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] 'find'
From: rog@vitanuova.com
In-Reply-To: <b774604a20f5f3d816d09e96585a901a@plan9.bell-labs.com>
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Date: Mon, 30 Jun 2003 15:07:59 +0100
Topicbox-Message-UUID: e179d988-eacb-11e9-9e20-41e7f4b1d025

> > 	grep pattern `{du -a /}
> >
> > leads to something like "grep: virtual memory allocation failure."
>
> Because the argument list to grep gets impossibly long.

there's a little version of xargs that i tend to use in these cases,
that i've attached, despite having posted it before as it hadn't been
updated for 4e and changes to the libraries mean that it can be
smaller than before.

e.g.
	du -a / | sed 's/^[^ 	]*[ 	]//' | xargs grep pattern

(note that awk '{print $1}' won't necessarily work instead of
the above sed since filenames can contain spaces).

#include <u.h>
#include <libc.h>
#include <bio.h>

#define NUMARGS 470
#define MAXSIZE 20000

void
run(char **cmd)
{
	char buf[256];
	int npid, pid;

	pid = fork();
	if (pid == -1) {
		perror("couldn't fork");
		exits("no forkage");
	}
	if (pid == 0) {
		if (cmd[0][0] != '/' && strncmp(cmd[0], "./", 2)) {
			snprint(buf, sizeof(buf), "/bin/%s", cmd[0]);
			exec(buf, cmd);
		} else {
			exec(cmd[0], cmd);
		}
		perror(cmd[0]);
		exits("no exec");
	}
	while ((npid = waitpid()) != pid && npid != -1)
		;
}

void
main(int argc, char **argv)
{
	char **cmd;
	int i, n, m, size, eof;
	Biobuf stdin;

	if (argc < 2) {
		fprint(2, "Usage: xargs cmd [args...]\n");
		exits("usage");
	}
	if (Binit(&stdin, 0, OREAD) == -1) {
		fprint(2, "couldn't init stdin\n");
		exits("error");
	}
	cmd = malloc((argc - 1 + NUMARGS + 1) * sizeof(char *));
	n = 0;
	for (i = 1; i < argc; i++)
		cmd[n++] = argv[i];

	for (;;) {
		eof = 0;
		size = 0;
		for (m = 0; m < NUMARGS && size < MAXSIZE; m++) {
			if ((cmd[n + m] = Brdstr(&stdin, '\n', 1)) == 0) {
				eof = 1;
				break;
			}
			size += Blinelen(&stdin);
		}
		cmd[n + m] = 0;
		if (m > 0)
			run(cmd);
		for (i = 0; i < m; i++)
			free(cmd[n+i]);
		if (eof)
			break;
	}
}