Userland: Improve head program

* allow specifying files as arguments, e.g. `head a b c`
* support multiple files
* print a filename header when multiple files are being printed
* allow suppression or forcing of filename header via flags

This change drops support for the legacy `-123` syntax in favour of the
more widely-supported `-n 123` form.

fixes #105

Userland/head.cpp

@@ -1,25 +1,97 @@
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <LibCore/CArgsParser.h>
+
+int head(const String& filename, bool print_filename, int line_count);
 
 int main(int argc, char** argv)
 {
- // FIXME: Allow setting via command-line argument.
+ CArgsParser args_parser("head");
+
+ args_parser.add_arg("n", "lines", "Number of lines to print (default 10)");
+ args_parser.add_arg("q", "Never print filenames");
+ args_parser.add_arg("v", "Always print filenames");
+
+ CArgsParserResult args = args_parser.parse(argc, (const char**)argv);
+
  int line_count = 10;
+ if (args.is_present("n")) {
+ line_count = strtol(args.get("n").characters(), NULL, 10);
+ if (errno) {
+ args_parser.print_usage();
+ return -1;
+ }
+ }
+
+ Vector<String> files = args.get_single_values();
+
+ bool print_filenames = files.size() > 1;
+
+ if (args.is_present("v")) {
+ print_filenames = true;
+ } else if (args.is_present("q")) {
+ print_filenames = false;
+ }
+
+ if (files.is_empty()) {
+ return head("", print_filenames, line_count);
+ }
+
+ int rc = 0;
+
+ for (auto &file : files) {
+ if (head(file, print_filenames, line_count) != 0) {
+ rc = 1;
+ }
+ }
+
+ return rc;
+}
+
+int head(const String& filename, bool print_filename, int line_count)
+{
+ bool is_stdin = false;
+ FILE* fp = nullptr;
+
+ if (filename == "" || filename == "-") {
+ fp = stdin;
+ is_stdin = true;
+ } else {
+ fp = fopen(filename.characters(), "r");
+ if (!fp) {
+ fprintf(stderr, "can't open %s for reading: %s\n", filename.characters(), strerror(errno));
+ return 1;
+ }
+ }
 
- if (argc > 1) {
- for (int i = 1; i < argc; ++i) {
- if (argv[i][0] == '-') {
-  line_count = atoi(&argv[i][1]);
- }
+ if (print_filename) {
+ if (is_stdin) {
+ puts("==> standard input <==");
+ } else {
+ printf("==> %s <==\n", filename.characters());
  }
  }
 
  for (int line = 0; line < line_count; ++line) {
  char buffer[BUFSIZ];
- auto* str = fgets(buffer, sizeof(buffer), stdin);
+ auto* str = fgets(buffer, sizeof(buffer), fp);
  if (!str)
  break;
- fputs(str, stdout);
+
+ // trim trailing newline character from string, since puts() will add
+ // its own newline anyway.
+ char *pos;
+ if ((pos = strchr(str, '\n')) != nullptr)
+ *pos = '\0';
+
+ puts(str);
+ }
+
+ fclose(fp);
+
+ if (print_filename) {
+ puts("");
  }
 
  return 0;