how to move the process in foreground [duplicate] - c

Question

This question already has answers here:
How to bring a child process running in the background to the foreground
(3 answers)
Closed 9 years ago.
I write similarity of the command bash interpreter.
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <fcntl.h>
#include <wait.h>
#include "shell.h"
#include <string.h>
char *infile;
char *outfile;
char *appfile;
struct command cmds[MAXCMDS];
char bkgrnd;
int k = 0;
static void my_wait(pid_t pid, pid_t bkgrnds[]);
int main(int argc,char *argv[])
{
int i;
char line[1024]; /* allow large command lines */
int ncmds;
char prompt[50]; /* shell prompt */
pid_t bkgrnds[1024]; /* for fg */
/* PLACE SIGNAL CODE HERE */
signal(SIGINT, SIG_IGN);
signal(SIGTSTP, SIG_IGN);
sprintf(prompt,"[%s] ",argv[0]);
while (promptline(prompt, line, sizeof(line)) > 0)
{ /* l eof */
if (0 >= (ncmds = parseline(line)))
{
continue; /* read next line */
}
#ifdef DEBUG
{
int i, j;
for (i = 0; i < ncmds; i++)
{
for (j = 0; NULL != cmds[i].cmdargs[j]; j++)
{
fprintf(stderr, "cmd[%d].cmdargs[%d] = %s\n", i, j, cmds[i].cmdargs[j]);
}
fprintf(stderr, "cmds[%d].cmdflag = %o\n", i, [i].cmdflag);
}
}
#endif
{
int previous_pipe_output = -1;
int pipeline_start = 0;
pid_t pids[MAXCMDS];
fprintf(stderr, "%d %s\n", ncmds, cmds[0].cmdargs[0]);
if (1 == ncmds && 0 == strcmp(cmds[0].cmdargs[0], "fg"))
{
if (0 == k)
{
fprintf(stderr, "k == 0\n");
continue;
}
int num = -1;
signal(SIGTTOU, SIG_IGN);
if (0 == cmds[0].cmdargs[1])
{
num = k - 1;
}
else
{
num = atoi(cmds[0].cmdargs[1]);
}
fprintf(stderr, "%d\n", bkgrnds[num]);
if(-1 == tcsetpgrp(STDIN_FILENO, bkgrnds[num]))
{
perror("Couldn't set terminal foreground process group");
return EXIT_FAILURE;
}
signal(SIGTTOU, SIG_DFL);
my_wait(bkgrnds[num], bkgrnds);
signal(SIGTTOU, SIG_IGN);
if (-1 == tcsetpgrp(STDIN_FILENO, getpgrp()))
{
perror("Couldn't set terminal foreground process group");
return EXIT_FAILURE;
}
signal(SIGTTOU, SIG_DFL);
continue;
}
for (i = 0; i < ncmds; i++)
{
int pipefd[2] = {-1, -1};
if(cmds[i].cmdflag & OUTPIP)
{
if(-1 == pipe(pipefd))
{
perror("Couldn't create pipe");
return EXIT_FAILURE;
}
}
{
/* FORK AND EXECUTE */
pids[i] = fork();
if (0 == pids[i])
{
signal(SIGINT, SIG_DFL);
signal(SIGTSTP, SIG_DFL);
if(-1 == setpgid(0, (cmds[i].cmdflag & INPIP)? pids[pipeline_start]:0))
{
perror("Couldn't set process group ID");
return EXIT_FAILURE;
}
if (!bkgrnd && !(cmds[i].cmdflag & INPIP))
{
signal(SIGTTOU, SIG_IGN);
if(-1 == tcsetpgrp(STDIN_FILENO, getpgrp()))
{
perror("Couldn't set terminal foreground process group");
return EXIT_FAILURE;
}
signal(SIGTTOU, SIG_DFL);
}
//....
execvp(cmds[i].cmdargs[0], cmds[i].cmdargs);
perror("Couldn't execute command");
return EXIT_FAILURE;
}
else if (-1 != pids[i])
{
if (!bkgrnd)
{
if (!(cmds[i].cmdflag & OUTPIP))
{
{
int j = 0;
for (j = pipeline_start; j <= i; j++)
{
my_wait(pids[j], bkgrnds);
}
}
signal(SIGTTOU, SIG_IGN);
if (-1 == tcsetpgrp(STDIN_FILENO, getpgrp()))
{
perror("Couldn't set terminal foreground process group");
return EXIT_FAILURE;
}
signal(SIGTTOU, SIG_DFL);
}
}
else
{
printf("Background process ID: %ld\n", (long)pids[i]);
}
}
else
{
perror("Couldn't create process");
}
}
}
}
} /* close while */
return EXIT_SUCCESS;
}
static void my_wait(pid_t pid, pid_t bkgrnds[])
{
int status = 0;
if (-1 != waitpid(pid, &status, WUNTRACED))
{
if (WIFSTOPPED(status) && (SIGTSTP == WSTOPSIG(status)))
{
bkgrnds[k++] = pid;
//printf("%d %d\n", pid, k);
kill(pid, SIGCONT);
bkgrnd = 1;
printf("Background process ID: %ld\n", (long)pid);
}
}
else
{
perror("Couldn't wait for child process termination");
}
}
Now I want to implement a command fg.
if (1 == ncmds && 0 == strcmp(cmds[0].cmdargs[0], "fg"))
{
if (0 == k)
{
fprintf(stderr, "k == 0\n");
continue;
}
int num = -1;
signal(SIGTTOU, SIG_IGN);
if (0 == cmds[0].cmdargs[1])
{
num = k - 1;
}
else
{
num = atoi(cmds[0].cmdargs[1]);
}
fprintf(stderr, "%d\n", bkgrnds[num]);
if(-1 == tcsetpgrp(STDIN_FILENO, bkgrnds[num]))
{
perror("Couldn't set terminal foreground process group");
return EXIT_FAILURE;
}
signal(SIGTTOU, SIG_DFL);
my_wait(bkgrnds[num], bkgrnds);
signal(SIGTTOU, SIG_IGN);
if (-1 == tcsetpgrp(STDIN_FILENO, getpgrp()))
{
perror("Couldn't set terminal foreground process group");
return EXIT_FAILURE;
}
signal(SIGTTOU, SIG_DFL);
continue;
}
Question : PID I know how do I bring to the foreground?
That is if I import
cat
CTRL + Z
fg
<- here shall continue cat
Thanks in advance.

Answer 1

Sorry. I just forgot to send SIGCONT process and everything. Added and working. kill(bkgrnds[num], SIGCONT);