Merge pull request #40 from fischerling/add-pager

add simple `more(1)` implementation and use it for man pages

files/usr/share/man/more.man

@@ -0,0 +1,13 @@
+SYNOPSIS
+    more [FILE]
+
+DESCRIPTION
+    more is a filter for paging through text one screenful at a time.
+
+OPTIONS
+    -h, --help: shows command help.
+
+KEY BINDINGS
+    q       Exit from more
+    space   Display next screen size
+    return  Display next line

programs/CMakeLists.txt

@@ -1,5 +1,6 @@
 # List of programs.
 set(PROGRAM_LIST
+    more.c
     chmod.c
     chown.c
     id.c

programs/man.c

@@ -40,7 +40,7 @@ int main(int argc, char *argv[])
     }
     else if (argc == 2)
     {
-        char *pager = "cat";
+        char *pager = "more";
         char filepath[PATH_MAX];
         strcpy(filepath, "/usr/share/man/");
         strcat(filepath, argv[1]);

programs/more.c

@@ -0,0 +1,97 @@
+/// @file more.c
+/// @brief `more` program.
+/// @copyright (c) 2014-2024 This file is distributed under the MIT License.
+/// See LICENSE.md for details.
+
+#include "stdbool.h"
+#include "stddef.h"
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/unistd.h>
+#include <strerror.h>
+#include <sys/stat.h>
+#include <termios.h>
+
+// Video dimensions defined in mentos/src/io/video.c
+#define HEIGHT       25
+#define WIDTH        80
+#define LAST_LINE    (HEIGHT - 1)
+
+static void erase_backwards(int n)
+{
+    for (int i = 0; i < n; i++) {
+        putchar('\b');
+    }
+}
+
+static void page_content(int fd)
+{
+    int lines = 0;
+    char line[WIDTH + 2];
+    char *lineend;
+    while((lineend = fgets(line, WIDTH, fd))) {
+        if (lineend - line == WIDTH && line[WIDTH-1] != '\n') {
+            line[WIDTH - 1] = '+';
+            line[WIDTH] = '\n';
+            line[WIDTH + 1] = 0;
+        }
+
+        printf("%s", line);
+
+        lines++;
+        if (lines == LAST_LINE) {
+            int prompt = printf("--more--");
+            int c;
+            bool_t quit = false;
+            do {
+                c = getchar();
+                if (c == 'q') {
+                    quit = true;
+                } else if (c == '\n') {
+                    lines = LAST_LINE - 1;
+                } else if (c == ' ') {
+                    lines = 0;
+                } else {
+                    continue;
+                }
+
+                break;
+            } while(1);
+            erase_backwards(prompt);
+            if (quit)
+                exit(EXIT_SUCCESS);
+        }
+    }
+}
+
+int main(int argc, char **argv)
+{
+    // Check if `--help` is provided.
+    for (int i = 1; i < argc; ++i) {
+        if ((strcmp(argv[i], "--help") == 0) || (strcmp(argv[i], "-h") == 0)) {
+            printf("Display the content of a file.\n");
+            printf("Usage:\n");
+            printf("    more [FILE]\n");
+            return 0;
+        }
+    }
+
+    struct termios _termios;
+    tcgetattr(STDIN_FILENO, &_termios);
+    _termios.c_lflag &= ~(ICANON | ECHO);
+    tcsetattr(STDIN_FILENO, 0, &_termios);
+
+    int fd = STDOUT_FILENO;
+    if (argc > 1) {
+        fd = open(argv[1], O_RDONLY, 0);
+        if (fd < 0) {
+            printf("more: %s: %s\n", argv[1], strerror(errno));
+            exit(EXIT_FAILURE);
+        }
+    }
+
+    page_content(fd);
+    return 0;
+}