On Sun, 27 Apr 2003, Anders Johansson wrote:

On Sunday 27 April 2003 18:33, Raúl Gutiérrez Segalés wrote:

...

Hi,

I am wondering how do I state in a C program that my input is comming from a pipe ?

For example:

ls | ./myprog

You get that on standard input, file descriptor 0

so read(stdin, buf, 100) shall do it ?

On Sunday 27 April 2003 20:10, Anders Johansson wrote:

#include #include

int main(int argc, char argv[]){ char buf[100]; ssize_t size;

size=read(0, buf, 100); if(size > 0){ buf[size]='\0';

printf("Received string: %s\n", buf); } exit(0); } <snip> #include

int main(int argc, char argv[]){ char buf[100]; size_t size;

size=fread(buf, 1, 100, stdin); if(size > 0){ buf[size]='\0';

printf("Received string: %s\n", buf); } exit(0); }

and yes, I'm aware of the bug in those programs :)

On Monday 28 April 2003 03:48, Raúl Gutiérrez Segalés wrote: <snip>

...

...

char buf[100];

<snip>

...

buf[size]='\0';

Enlight me, I only see one, no protection against buffer overflows..

That would be the one. There is a protection against buffer overflows, in that both read and fread state how many bytes they want. Sadly, I wrote it a bit too quickly, and potentially 101 bytes could be put in a 100 byte buffer. Oh well, whaddyawant for a nickel, a rubber biscuit?

While checking the mailq on the BLU server yesterday I noticed over 300 messages queued up for a single user (from a listserv). postfix has a program, postsuper that can be used to delete email from the queue, but first the mail queue needs to be parsed. Simple solution in C: Use the popen(3) function: Here is a short code fragment: #include #include #include int main() { FILE *ipipe; char buf[256]; if ((ipipe = popen("mailq", "r")) == NULL) { fprintf(stderr, "Popen error:%s\n", strerror(errno)); exit(-1); while (fgets(buf, sizeof(buf), ipipe)) { /**** process the buffer **** The first line contains the queue id, subsequent **** lines contain email addresses and error messages **** each queue id is terminated by an empty line. ****/ } pclose(ipipe); return 0; } In my case, I put all the queue entries into a linked list and matched them to some keywords entered by the user then built another command for postsuper. You can do a similar thing with postsuper by calling it once with input from standard input: /* Code frag */ FILE *opipe; if ((opipe = popen("postsuper -d -", "w")) == NULL) { fprintf(stderr, "Popen error:%s\n", strerror(errno)); exit(-1); /* foreach queue id to be deleted */ printf("%s", ll->qid); /* End foreach */ pclose(opipe); -- Jerry Feldman Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9

On Mon, 28 Apr 2003 17:17:55 +0200 Anders Johansson wrote:

On Monday 28 April 2003 16:51, Jerry Feldman wrote:

...

In my case, I put all the queue entries into a linked list and matched them to some keywords entered by the user then built another command for postsuper. You can do a similar thing with postsuper by calling it once with input from standard input: /* Code frag */ FILE *opipe; if ((opipe = popen("postsuper -d -", "w")) == NULL) { fprintf(stderr, "Popen error:%s\n", strerror(errno)); exit(-1); /* foreach queue id to be deleted */ printf("%s", ll->qid);

typo?

fprintf(opipe, "%s", ll-qid); Yes, I stand corrected. In any case it works fine. IMHO, I think that the most useful thing that Ken Thompson put into Unix was pipes.

-- Jerry Feldman Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9