jp27+@andrew.cmu.edu (Jacques Parker) (12/13/89)
I made the following program. When compiled & run, it will accept
input, but not act on it. It should accept commands, and the child
process should receive and execute them. This
does not happen until the program is terminated (Enter ^D). Any ideas?
How do I insure that the child receives the parents output immediately?
Thank you for any help.
Jacques Parker
#include <stdio.h>
#define MAXLEN 100
#define ST_INP 0
#define ST_OUT 1
extern char **environ;
char **arg = { "/bin/csh","-x"};
main(argc,argv,envp)
int argc;
char **argv, **envp;
{
int pd[2];
int pid;
int bak_inp = dup (ST_INP);/* Backup the input FD */
int bak_out = dup (ST_OUT);/* Backup the output FD */
if (pipe(pd) < 0)
printf("%s: Can't create pipe", cmd);
dup2(pd[1], ST_OUT); /* ST_OUT --> pipe WRITE */
dup2(pd[0], ST_INP); /* ST_INP --> pipe READ */
if ((pid = fork()) < 0)
printf("%s: Can't spawn a process.", cmd);
if (pid == 0) {
dup2(bak_out, ST_OUT); /* child out --> ST_OUT */
/* child in --> Pipe READ */
execvp(arg[0],arg,environ);
printf("Shell not started. '%s' failed.",cmd);
}
dup2(bak_inp,ST_INP); /* parent out --> Pipe WRITE */
/* parent in --> ST_INP */
while (gets(cmd) != NULL) { /* Enter ^D to end. */
printf("%s\n,cmd);
fflush(NULL);
}
}
Address: internet jp27+@andrew.cmu.edu,
uucp ...!{harvard,uunet}!andrew.cmu.edu!jp27,
bitnet jp27%andrew@cmccvb.bitnet.caag@inf.rl.ac.uk (Crispin Goswell) (12/14/89)
In article <21729@adm.BRL.MIL> jp27+@andrew.cmu.edu (Jacques Parker) writes: > >I made the following program. When compiled & run, it will accept >input, but not act on it. As listed here it did not compile at all on the systems that I have to hand. >It should accept commands, and the child >process should receive and execute them. This >does not happen until the program is terminated (Enter ^D). Any ideas? >How do I insure that the child receives the parents output immediately? > >Thank you for any help. > > Jacques Parker > > >#include <stdio.h> > >#define MAXLEN 100 >#define ST_INP 0 >#define ST_OUT 1 > >extern char **environ; > >char **arg = { "/bin/csh","-x"}; I had to replace this with: char *arg[] = { "/bin/csh","-x",NULL }; the [] to get it to compile, and NULL to get execvp to work when it ran. > >main(argc,argv,envp) >int argc; >char **argv, **envp; >{ > > int pd[2]; > int pid; > int bak_inp = dup (ST_INP);/* Backup the input FD */ > int bak_out = dup (ST_OUT);/* Backup the output FD */ I added: char cmd[BUFSIZ]; here to get it to compile. This is optimistic: the gets() does not check for buffer overflow. > if (pipe(pd) < 0) > printf("%s: Can't create pipe", cmd); > > dup2(pd[1], ST_OUT); /* ST_OUT --> pipe WRITE */ > dup2(pd[0], ST_INP); /* ST_INP --> pipe READ */ > > if ((pid = fork()) < 0) > printf("%s: Can't spawn a process.", cmd); > if (pid == 0) { > dup2(bak_out, ST_OUT); /* child out --> ST_OUT */ > /* child in --> Pipe READ */ > execvp(arg[0],arg,environ); > printf("Shell not started. '%s' failed.",cmd); > } > > dup2(bak_inp,ST_INP); /* parent out --> Pipe WRITE */ > /* parent in --> ST_INP */ > > while (gets(cmd) != NULL) { /* Enter ^D to end. */ > printf("%s\n,cmd); I had to add the " here: printf("%s\n",cmd); > fflush(NULL); I had to replace this with: fflush (stdout); to get the program to work. > } This article probably belongs in comp.lang.c. Name: Crispin Goswell |-------|__ Informatics Department UUCP: {... | mcvax}!ukc!rlinf!caag | Tea | | Rutherford Appleton Lab JANET: caag@uk.ac.rl.inf \ Mug /_/ Chilton, Didcot ARPA: caag%inf.rl.ac.uk@nsfnet-relay.ac.uk \_____/ Oxon OX11 0QX, UK "Where are you when the Sun goes down? You're so far away from me." - Dire Straits