feat(cli): add grep command

Implements grep <text> <file> for searching text inside files.

Supported options:
  -n    Show line numbers
  -i    Case-insensitive search
  -c    Print match count only
  -h    Show help

Closes part of #22

src/userland/cli/grep.c

@@ -0,0 +1,148 @@
+// Copyright (c) 2023-2026 Chris (boreddevnl)
+// This software is released under the GNU General Public License v3.0. See LICENSE file for details.
+// This header needs to maintain in any file it is present in, as per the GPL license terms.
+// BOREDOS_APP_DESC: Search for text inside a file.
+
+#include "../libc/syscall.h"
+#include "../libc/stdlib.h"
+#include "../libc/string.h"
+#include "../libc/stdio.h"
+
+#define READ_BUF_SIZE 4096
+#define LINE_BUF_SIZE 1024
+
+static int sc_strcmp(const char *a, const char *b) {
+    while (*a && *a == *b) { a++; b++; }
+    return (unsigned char)*a - (unsigned char)*b;
+}
+
+static void print_usage(void) {
+    printf("Usage: grep [options] <text> <file>\n");
+    printf("\n");
+    printf("Search for text inside a file.\n");
+    printf("\n");
+    printf("Options:\n");
+    printf("  -n    Show line numbers\n");
+    printf("  -i    Case-insensitive search\n");
+    printf("  -c    Print match count only\n");
+    printf("  -h    Show this help\n");
+}
+
+static char to_lower(char c) {
+    if (c >= 'A' && c <= 'Z') return c + 32;
+    return c;
+}
+
+static int str_contains(const char *haystack, const char *needle, int ignore_case) {
+    int h_len = (int)strlen(haystack);
+    int n_len = (int)strlen(needle);
+
+    if (n_len == 0) return 1;
+    if (n_len > h_len) return 0;
+
+    for (int i = 0; i <= h_len - n_len; i++) {
+        int match = 1;
+        for (int j = 0; j < n_len; j++) {
+            char h = ignore_case ? to_lower(haystack[i + j]) : haystack[i + j];
+            char n = ignore_case ? to_lower(needle[j]) : needle[j];
+            if (h != n) { match = 0; break; }
+        }
+        if (match) return 1;
+    }
+    return 0;
+}
+
+int main(int argc, char **argv) {
+    int show_numbers = 0;
+    int ignore_case  = 0;
+    int count_only   = 0;
+    int arg_offset   = 1;
+
+    for (int i = 1; i < argc; i++) {
+        if (argv[i][0] != '-') break;
+        if (sc_strcmp(argv[i], "-n") == 0) {
+            show_numbers = 1; arg_offset++;
+        } else if (sc_strcmp(argv[i], "-i") == 0) {
+            ignore_case = 1; arg_offset++;
+        } else if (sc_strcmp(argv[i], "-c") == 0) {
+            count_only = 1; arg_offset++;
+        } else if (sc_strcmp(argv[i], "-h") == 0 ||
+                   sc_strcmp(argv[i], "--help") == 0) {
+            print_usage();
+            return 0;
+        } else {
+            printf("grep: unknown option '%s'\n", argv[i]);
+            return 1;
+        }
+    }
+
+    if (argc - arg_offset < 2) {
+        print_usage();
+        return 1;
+    }
+
+    const char *pattern = argv[arg_offset];
+    const char *path    = argv[arg_offset + 1];
+
+    int fd = sys_open(path, "r");
+    if (fd < 0) {
+        printf("grep: cannot open '%s'\n", path);
+        return 1;
+    }
+
+    static char read_buf[READ_BUF_SIZE];
+    static char line[LINE_BUF_SIZE];
+    int line_pos  = 0;
+    int line_num  = 0;
+    int match_cnt = 0;
+
+    while (1) {
+        int bytes = sys_read(fd, read_buf, READ_BUF_SIZE);
+        if (bytes <= 0) break;
+
+        for (int i = 0; i < bytes; i++) {
+            char c = read_buf[i];
+
+            if (c == '\n' || line_pos >= LINE_BUF_SIZE - 1) {
+                line[line_pos] = '\0';
+                line_num++;
+
+                if (str_contains(line, pattern, ignore_case)) {
+                    match_cnt++;
+                    if (!count_only) {
+                        if (show_numbers)
+                            printf("%d: %s\n", line_num, line);
+                        else
+                            printf("%s\n", line);
+                    }
+                }
+
+                line_pos = 0;
+            } else if (c != '\r') {
+                line[line_pos++] = c;
+            }
+        }
+    }
+
+    // Handle last line if file doesn't end with newline
+    if (line_pos > 0) {
+        line[line_pos] = '\0';
+        line_num++;
+        if (str_contains(line, pattern, ignore_case)) {
+            match_cnt++;
+            if (!count_only) {
+                if (show_numbers)
+                    printf("%d: %s\n", line_num, line);
+                else
+                    printf("%s\n", line);
+            }
+        }
+    }
+
+    sys_close(fd);
+
+    if (count_only)
+        printf("%d\n", match_cnt);
+
+    return match_cnt > 0 ? 0 : 1;
+}