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Serenity Operating System
1/*
2 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 *
8 * 1. Redistributions of source code must retain the above copyright notice, this
9 * list of conditions and the following disclaimer.
10 *
11 * 2. Redistributions in binary form must reproduce the above copyright notice,
12 * this list of conditions and the following disclaimer in the documentation
13 * and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
16 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
21 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
22 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
23 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
24 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include <AK/StdLibExtras.h>
28#include <LibCore/ArgsParser.h>
29
30#include <errno.h>
31#include <stdio.h>
32#include <stdlib.h>
33
34int head(const String& filename, bool print_filename, int line_count, int char_count);
35
36int main(int argc, char** argv)
37{
38 if (pledge("stdio rpath", nullptr) < 0) {
39 perror("pledge");
40 return 1;
41 }
42
43 int line_count = 0;
44 int char_count = 0;
45 bool never_print_filenames = false;
46 bool always_print_filenames = false;
47 Vector<const char*> files;
48
49 Core::ArgsParser args_parser;
50 args_parser.add_option(line_count, "Number of lines to print (default 10)", "lines", 'n', "number");
51 args_parser.add_option(char_count, "Number of characters to print", "characters", 'c', "number");
52 args_parser.add_option(never_print_filenames, "Never print file names", "quiet", 'q');
53 args_parser.add_option(always_print_filenames, "Always print file names", "verbose", 'v');
54 args_parser.add_positional_argument(files, "File to process", "file", Core::ArgsParser::Required::No);
55 args_parser.parse(argc, argv);
56
57 if (line_count == 0 && char_count == 0) {
58 line_count = 10;
59 }
60
61 bool print_filenames = files.size() > 1;
62 if (always_print_filenames)
63 print_filenames = true;
64 else if (never_print_filenames)
65 print_filenames = false;
66
67 if (files.is_empty()) {
68 return head("", print_filenames, line_count, char_count);
69 }
70
71 int rc = 0;
72
73 for (auto& file : files) {
74 if (head(file, print_filenames, line_count, char_count) != 0) {
75 rc = 1;
76 }
77 }
78
79 return rc;
80}
81
82int head(const String& filename, bool print_filename, int line_count, int char_count)
83{
84 bool is_stdin = false;
85 FILE* fp = nullptr;
86
87 if (filename == "" || filename == "-") {
88 fp = stdin;
89 is_stdin = true;
90 } else {
91 fp = fopen(filename.characters(), "r");
92 if (!fp) {
93 fprintf(stderr, "can't open %s for reading: %s\n", filename.characters(), strerror(errno));
94 return 1;
95 }
96 }
97
98 if (print_filename) {
99 if (is_stdin) {
100 puts("==> standard input <==");
101 } else {
102 printf("==> %s <==\n", filename.characters());
103 }
104 }
105
106 if (line_count) {
107 for (int line = 0; line < line_count; ++line) {
108 char buffer[BUFSIZ];
109 auto* str = fgets(buffer, sizeof(buffer), fp);
110 if (!str)
111 break;
112
113 // specifically use fputs rather than puts, because fputs doesn't add
114 // its own newline.
115 fputs(str, stdout);
116 }
117 } else if (char_count) {
118 char buffer[BUFSIZ];
119
120 while (char_count) {
121 int nread = fread(buffer, 1, min(BUFSIZ, char_count), fp);
122 if (nread > 0) {
123 int ncomplete = 0;
124
125 while (ncomplete < nread) {
126 int nwrote = fwrite(&buffer[ncomplete], 1, nread - ncomplete, stdout);
127 if (nwrote > 0)
128 ncomplete += nwrote;
129
130 if (feof(stdout)) {
131 fprintf(stderr, "unexpected eof writing to stdout\n");
132 return 1;
133 }
134
135 if (ferror(stdout)) {
136 fprintf(stderr, "error writing to stdout\n");
137 return 1;
138 }
139 }
140 }
141
142 char_count -= nread;
143
144 if (feof(fp))
145 break;
146
147 if (ferror(fp)) {
148 fprintf(stderr, "error reading input\n");
149 break;
150 }
151 }
152 }
153
154 fclose(fp);
155
156 if (print_filename) {
157 puts("");
158 }
159
160 return 0;
161}