89 lines
1.5 KiB
C
89 lines
1.5 KiB
C
/* head - print the first few lines of a file Author: Andy Tanenbaum */
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#include <errno.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#define DEFAULT 10
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_PROTOTYPE(int main, (int argc, char **argv));
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_PROTOTYPE(void do_file, (int n, FILE *f));
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_PROTOTYPE(void usage, (void));
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int main(argc, argv)
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int argc;
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char *argv[];
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{
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FILE *f;
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int legacy, n, k, nfiles;
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char *ptr;
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/* Check for flags. One can only specify how many lines to print. */
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k = 1;
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n = DEFAULT;
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legacy = 0;
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for (k = 1; k < argc && argv[k][0] == '-'; k++) {
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ptr = &argv[k][1];
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if (ptr[0] == 'n' && ptr[1] == 0) {
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k++;
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if (k >= argc) usage();
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ptr = argv[k];
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}
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else if (ptr[0] == '-' && ptr[1] == 0) {
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k++;
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break;
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}
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else if (++legacy > 1) usage();
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n = atoi(ptr);
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if (n <= 0) usage();
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}
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nfiles = argc - k;
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if (nfiles == 0) {
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/* Print standard input only. */
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do_file(n, stdin);
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exit(0);
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}
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/* One or more files have been listed explicitly. */
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while (k < argc) {
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if (nfiles > 1) printf("==> %s <==\n", argv[k]);
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if ((f = fopen(argv[k], "r")) == NULL)
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fprintf(stderr, "%s: cannot open %s: %s\n",
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argv[0], argv[k], strerror(errno));
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else {
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do_file(n, f);
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fclose(f);
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}
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k++;
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if (k < argc) printf("\n");
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}
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return(0);
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}
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void do_file(n, f)
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int n;
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FILE *f;
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{
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int c;
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/* Print the first 'n' lines of a file. */
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while (n) switch (c = getc(f)) {
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case EOF:
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return;
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case '\n':
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--n;
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default: putc((char) c, stdout);
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}
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}
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void usage()
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{
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fprintf(stderr, "Usage: head [-lines | -n lines] [file ...]\n");
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exit(1);
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}
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