105 lines
2.2 KiB
C
105 lines
2.2 KiB
C
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#include <stdbool.h>
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#include <stdio.h>
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#include <string.h>
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#include <syscall.h>
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static void read_line (char line[], size_t);
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static bool backspace (char **pos, char line[]);
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int
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main (void)
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{
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printf ("Shell starting...\n");
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for (;;)
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{
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char command[80];
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/* Read command. */
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printf ("--");
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read_line (command, sizeof command);
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/* Execute command. */
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if (!strcmp (command, "exit"))
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break;
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else if (!memcmp (command, "cd ", 3))
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{
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if (!chdir (command + 3))
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printf ("\"%s\": chdir failed\n", command + 3);
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}
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else if (command[0] == '\0')
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{
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/* Empty command. */
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}
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else
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{
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pid_t pid = exec (command);
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if (pid != PID_ERROR)
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printf ("\"%s\": exit code %d\n", command, wait (pid));
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else
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printf ("exec failed\n");
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}
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}
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printf ("Shell exiting.");
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return EXIT_SUCCESS;
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}
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/* Reads a line of input from the user into LINE, which has room
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for SIZE bytes. Handles backspace and Ctrl+U in the ways
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expected by Unix users. On return, LINE will always be
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null-terminated and will not end in a new-line character. */
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static void
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read_line (char line[], size_t size)
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{
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char *pos = line;
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for (;;)
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{
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char c;
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read (STDIN_FILENO, &c, 1);
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switch (c)
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{
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case '\r':
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*pos = '\0';
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putchar ('\n');
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return;
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case '\b':
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backspace (&pos, line);
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break;
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case ('U' - 'A') + 1: /* Ctrl+U. */
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while (backspace (&pos, line))
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continue;
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break;
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default:
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/* Add character to line. */
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if (pos < line + size - 1)
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{
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putchar (c);
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*pos++ = c;
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}
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break;
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}
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}
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}
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/* If *POS is past the beginning of LINE, backs up one character
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position. Returns true if successful, false if nothing was
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done. */
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static bool
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backspace (char **pos, char line[])
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{
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if (*pos > line)
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{
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/* Back up cursor, overwrite character, back up
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again. */
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printf ("\b \b");
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(*pos)--;
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return true;
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}
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else
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return false;
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}
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