add tail

7 files changed, 115 insertions, 4 deletions

diff --git a/readme.md b/readme.md
index 3dfe6e5..3440299 100644
--- a/readme.md
+++ b/readme.md
@@ -4,7 +4,7 @@
 A terrible busybox/gnu coreutils clone.
 
 Currently the only supported commands are: 
-`dd`, `cat`, `yes`, `echo`, `printf`, `id`, `groups`, `ls`
+`dd`, `cat`, `yes`, `echo`, `printf`, `id`, `groups`, `ls`, `tail`
  
 ## How to
 
diff --git a/src/command.h b/src/command.h
index 4a2c50b..939886d 100644
--- a/src/command.h
+++ b/src/command.h
@@ -17,3 +17,4 @@ COMMAND(print);
 COMMAND_EMPTY(groups);
 COMMAND_EMPTY(user_id);
 COMMAND(ls);
+COMMAND(tail);
diff --git a/src/commands/cat.c b/src/commands/cat.c
index f5622e8..8e22706 100644
--- a/src/commands/cat.c
+++ b/src/commands/cat.c
@@ -1,7 +1,9 @@
 #include "../command.h"
 
 #include <ctype.h>
+#include <errno.h>
 #include <string.h>
+#include <sys/stat.h>
 
 struct Flags {
     bool number_lines;
@@ -138,6 +140,15 @@ COMMAND(cat) {
             continue;
         } else {
             files = true;
+            struct stat s;
+            if (stat(argv[i], &s) < 0) {
+                printf("error: failed to read %s: %s\n", argv[i], strerror(errno));
+                continue;
+            }
+            if (!S_ISREG(s.st_mode)) {
+                printf("error: %s is not a file\n", argv[i]);
+                continue;
+            }
             FILE* in = get_file(argv[i], "r");
             cat_file(in, flags);
             fclose(in);
diff --git a/src/commands/tail.c b/src/commands/tail.c
new file mode 100644
index 0000000..04f7f42
--- /dev/null
+++ b/src/commands/tail.c
@@ -0,0 +1,80 @@
+#include "../command.h"
+
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+
+static void tail_file(FILE* file) {
+    char* ring[10];
+    memset(ring, 0, sizeof(char*) * 10);
+
+    int ring_len[10];
+    
+    int index = 0;
+    int size = 0;
+
+    int read;
+    size_t len = 0;
+    char* line = NULL;
+    while ((read = getline(&line, &len, file)) != -1) {
+
+        if (ring[index] != NULL) free(ring[index]);
+        ring[index] = line;
+        ring_len[index] = read;
+
+        index++;
+        index %= 10;
+        if (size < 10) size++;
+
+        line = NULL;
+    }
+
+    index += 10 - size;
+    index %= 10;
+    
+    for (int i = 0; i < size; i++) {
+        fwrite(ring[index], ring_len[index], 1, stdout);
+        free(ring[index]);
+        index += 1;
+        index %= 10;
+    }
+
+    free(line);
+    fclose(file);
+}
+
+static void help() {
+    printf("Usage: tail [FILE]...\n\n");
+    printf("Print last 10 lines of FILEs (or stdin) to.\n");
+    printf("With more than one FILE, precede each with a filename header.\n");
+    exit(EXIT_SUCCESS);
+}
+
+COMMAND(tail) {
+    if (argc < 1) {
+        tail_file(stdin);
+        return EXIT_SUCCESS;
+    }
+
+    if (streql(argv[0], "--help")) help();
+
+    if (argc == 1) {
+        FILE* file = get_file(argv[0], "r");
+        tail_file(file);
+        return EXIT_SUCCESS;
+    }
+
+    for (int i = 0; i < argc; i++) {
+        FILE* file;
+        if (streql("-", argv[i])) {
+            file = stdin;
+        } else {
+            file = get_file_s(argv[i], "r");
+            if (file == NULL) continue;
+        }
+        printf("\n==> %s <==\n", argv[i]);
+        tail_file(file);
+    }
+
+    return EXIT_SUCCESS;
+}
diff --git a/src/main.c b/src/main.c
index 63aa775..ce89210 100644
--- a/src/main.c
+++ b/src/main.c
@@ -20,7 +20,7 @@ int main (ARGUMENTS) {
         if (argc < 2) {
             printf("usage: lazysphere [function [arguments]...]\n\n");
             printf("currently defined functions:\n");
-            printf("\tdd, cat, yes, echo, printf, id, groups, ls\n");
+            printf("\tdd, cat, yes, echo, printf, id, groups, ls, tail\n");
             return EXIT_SUCCESS;
         }
         argc--;
@@ -50,6 +50,8 @@ int main (ARGUMENTS) {
         return user_id();
     } else if (streql(cmd, "ls")) {
         return ls(NEXT_ARGS);
+    } else if (streql(cmd, "tail")) {
+        return tail(NEXT_ARGS);
     } else {
         error("error: invalid command %s", cmd);
     }
diff --git a/src/shared.c b/src/shared.c
index b167e6f..8d0dcca 100644
--- a/src/shared.c
+++ b/src/shared.c
@@ -5,6 +5,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+#include <sys/stat.h>
 
 void error(const char* format, ...) {
     va_list list;
@@ -15,14 +16,29 @@ void error(const char* format, ...) {
     exit(EXIT_FAILURE);
 }
 
-FILE* get_file(const char* path, const char* type) {
+FILE* get_file_s(const char* path, const char* type) {
+    struct stat s;
+    if (stat(path, &s) < 0) {
+        fprintf(stderr, "error: failed to read %s: %s\n", path, strerror(errno));
+        return NULL;
+    }
+    if (!S_ISREG(s.st_mode)) {
+        fprintf(stderr, "error: %s is not a file\n", path);
+        return NULL;
+    }
     FILE* file = fopen(path, type);
     if (file == NULL) {
-        error("error: failed to open file %s: %s", path, strerror(errno));
+        fprintf(stderr, "error: failed to open file %s: %s\n", path, strerror(errno));
     }
     return file;
 }
 
+FILE* get_file(const char* path, const char* type) {
+    FILE* file = get_file_s(path, type);
+    if (file == NULL) exit(EXIT_FAILURE);
+    return file;
+}
+
 long int get_number(const char* text) {
     char* end;
     long int n = strtol(text, &end, 10);
diff --git a/src/shared.h b/src/shared.h
index 4556d5d..251a993 100644
--- a/src/shared.h
+++ b/src/shared.h
@@ -7,6 +7,7 @@
 __attribute__ ((__format__(printf, 1, 2)))
 void error(const char* format, ...);
 
+FILE* get_file_s(const char* path, const char* type);
 FILE* get_file(const char* path, const char* type);
 long int get_number(const char* text);