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POHow can I design a signal-safe shell interpreter
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copied!<p>The code I have right now sends a prompt out to stdout, then reads a line from stdin. Receiving <code>SIGINT</code> at any point interrupts execution and exits the program. I am unsure where I should trap <code>SIGINT</code>, and I know that I cannot start a new prompt when the signal is received with my current code. Is there a proper way to accomplish that (ultimate goal would be for it to act like most shells (SIGINT cancels the current prompt and starts a new one))?</p> <p>This code will run on Linux, but the less platform independent, the better.</p> <p><code>get_line</code> reads a line from stdin into a buffer and generates a char[], which is assigned to line.<br> <code>split_args</code> takes a line and transforms it into an array of char[], splitting on whitespace.<br> <code>is_command_valid</code> determines if the user typed a known internal command. External programs cannot be executed.</p> <pre><code>static int run_interactive(char *user) { int done = 0; do { char *line, **args; int (*fn)(char *, char **); fprintf(stderr, "gitorium (%s)> ", user); get_line(&line); if (line[0] == '\0') { free(line); break; } split_args(&args, line); if (!strcmp(args[0], "quit") || !strcmp(args[0], "exit") || !strcmp(args[0], "logout") || !strcmp(args[0], "bye")) done = 1; else if (NULL == args[0] || (!strcmp("help", args[0]) && NULL == args[1])) interactive_help(); else if ((fn = is_command_valid(args)) != NULL) (*fn)(user, args); else error("The command does not exist."); free(line); free(args); } while (!done); return 0; } </code></pre> <p>Here are the two most important helper functions</p> <pre><code>static int split_args(char ***args, char *str) { char **res = NULL, *p = strtok(str, " "); int n_spaces = 0, i = 0; while (p) { res = realloc(res, sizeof (char*) * ++n_spaces); if (res == NULL) return GITORIUM_MEM_ALLOC; res[n_spaces-1] = p; i++; p = strtok(NULL, " "); } res = realloc(res, sizeof(char*) * (n_spaces+1)); if (res == NULL) return GITORIUM_MEM_ALLOC; res[n_spaces] = 0; *args = res; return i; } static int get_line(char **linep) { char *line = malloc(LINE_BUFFER_SIZE); int len = LINE_BUFFER_SIZE, c; *linep = line; if(line == NULL) return GITORIUM_MEM_ALLOC; for(;;) { c = fgetc(stdin); if(c == EOF || c == '\n') break; if(--len == 0) { char *linen = realloc(*linep, sizeof *linep + LINE_BUFFER_SIZE); if(linen == NULL) return GITORIUM_MEM_ALLOC; len = LINE_BUFFER_SIZE; line = linen + (line - *linep); *linep = linen; } *line++ = c; } *line = 0; return 0; } </code></pre>

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