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/*
Homework n.5
Estendere l'esempio 'nanoshell.c' ad una shell piu' realistica in cui
si possono:
- passare argomenti al comando invocato (per semplicita', assumiamo
che questi non contengano spazi);
- usare la redirezione dei canali di input/output/error;
- mandare un comando in esecuzione in background (con la '&' finale).
Esempi di invocazione che la shell dovrebbe supportare sono:
$ cal 3 2015
$ cp /etc/passwd /etc/hosts /tmp
$ cat /tmp/passwd
$ cat filechenonesiste 2>/dev/null
$ ls -R /etc/ &
*/
#include
#include
#include
#include
#include
#include
#include
#define LEN_BUFFER 2048
#define DELIM " "
#define MAX_ARGS 30
#define STDIN 0
#define STDOUT 1
#define STDERR 2
int main(int argc, char *argv[]) {
char commandline[LEN_BUFFER];
int pid, len, i, fd;
char *token;
char *args[MAX_ARGS];
char bckg_exec;
char *path_stdout, *path_stdin, *path_stderr;
while (1) {
printf("> ");
fgets(commandline, LEN_BUFFER, stdin);
len = strlen(commandline);
if ( commandline[len-1] == '\n')
commandline[len-1] = '\0';
if ((strcmp(commandline, "exit") == 0) || (strcmp(commandline, "quit") == 0))
break;
if ((token = strtok(commandline, DELIM)) == NULL) {
fprintf(stderr, "la riga di comando sembra malformata!\n");
continue;
}
i = 0;
bckg_exec = 0;
path_stdout = path_stdin = path_stderr = NULL;
do {
/* controlla se si tratta del simbolo '&' che indica una esecuzione
in background del comando */
if ((strlen(token) == 1) && token[0] == '&') {
bckg_exec = 1;
continue;
}
/* controlla se si tratta di una redirezione dei canali */
if (token[0] == '<') {
if (path_stdin == NULL) {
path_stdin = strdup(token+1);
if (!access(path_stdin, R_OK)) {
fprintf(stderr, "impossibile accedere in lettura al file specificato come standard input!\n");
free(path_stdin);
continue;
}
} else {
fprintf(stderr, "doppia redirezione dello standard input!\n");
continue;
}
continue;
/* TO FIX: sintassi inesatta, qui implementa '>2' piuttosto che '2>' */
} else if (token[0] == '>') {
if (token[1] == '2') {
if (path_stderr == NULL) {
path_stderr = strdup(token+2);
} else {
fprintf(stderr, "doppia redirezione dello standard error!\n");
continue;
}
} else {
if (path_stdout == NULL) {
path_stdout = strdup(token+1);
} else {
fprintf(stderr, "doppia redirezione dello standard output!\n");
continue;
}
}
continue;
}
args[i++] = strdup(token);
} while ((token = strtok(NULL, DELIM)) != NULL);
args[i] = NULL;
pid = fork();
if ( pid == -1 ) {
perror("fork");
exit(1);
}
if ( pid == 0 ) {
/* applica l'eventuale redirezione dei canali nel figlio */
if (path_stdin != NULL) {
fd = open(path_stdin, O_RDONLY);
close(STDIN);
dup(fd);
}
if (path_stderr != NULL) {
fd = open(path_stderr, O_WRONLY|O_CREAT|O_TRUNC, 0666);
close(STDERR);
dup(fd);
}
if (path_stdout != NULL) {
fd = open(path_stdout, O_WRONLY|O_CREAT|O_TRUNC, 0666);
close(STDOUT);
dup(fd);
}
execvp(args[0], args);
fprintf(stderr, "Errore nell'esecuzione di '%s'\n", args[0]);
exit (2);
} else if (!bckg_exec)
wait(NULL);
/* libero la memoria allocata dinamicamente nel padre */
if (path_stdin != NULL) free(path_stdin);
if (path_stderr != NULL) free(path_stderr);
if (path_stdout != NULL) free(path_stdout);
i = 0;
while (args[i] != NULL)
free(args[i++]);
}
exit(0);
}