First commit of that cat(1) clone I'm making

6 files changed, 161 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..5831686
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,9 @@
+CC = gcc
+CFLAGS = -ansi -pedantic-errors
+
+cat : main.o cfn.o cfd.o 
+	gcc -o cat main.o cfn.o cfd.o
+
+clean :
+	rm -f -- cat *.o
+
diff --git a/README.markdown b/README.markdown
new file mode 100644
index 0000000..b97f4a4
--- /dev/null
+++ b/README.markdown
@@ -0,0 +1,18 @@
+cat(1)
+======
+
+Very naive implementation of `cat(1)` with no options, for me to learn a bit
+more C and the toolchain around it. Supports reading from stdin if there are no
+arguments, but that's as clever as it gets.
+
+To build, just do:
+
+    $ make
+
+Author
+:   Tom Ryder <tom@sanctum.geek.nz>
+Copyright
+:   2016
+License
+:   Public domain
+
diff --git a/cat.h b/cat.h
new file mode 100644
index 0000000..c8db240
--- /dev/null
+++ b/cat.h
@@ -0,0 +1,24 @@
+#ifndef CAT_H
+#define CAT_H
+
+/* Whole bunch of headers I only sort-of understand that are used for the
+ * various system functions in the source files */
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+/* How big the buffer is to hold the bytes for the read-write cycle from each
+ * file descriptor */
+#define BUFLEN (2 << 12)
+
+/* Function prototypes so that I can refer to these functions in main() before
+ * I actually define them */
+int cfn(const char *fn, void *buf);
+int cfd(int fd, void *buf);
+
+#endif
+
diff --git a/cfd.c b/cfd.c
new file mode 100644
index 0000000..9e8baa6
--- /dev/null
+++ b/cfd.c
@@ -0,0 +1,30 @@
+#include "cat.h"
+
+/* Function writes the contents of an opened file descriptor to stdout */
+int cfd(int fd, void *buf) {
+    int br;
+
+    /* Use the buffer to read the file in blocks, writing each block to stdout
+     * as we go */
+    while ((br = read(fd, buf, BUFLEN)) > 0) {
+        fwrite(buf, 1, br, stdout);
+    }
+
+    /* If the last return value for br() was -1, there was an error; 0 is what
+     * we expect */
+    if (br == -1) {
+        perror(__FUNCTION__);
+        return -1;
+    }
+
+    /* Force a write of any still-buffered data to stdout */
+    if (fflush(stdout) != 0) {
+        perror(__FUNCTION__);
+        return -1;
+    }
+
+    /* Return success, since apparently nothing went wrong before we got here
+     * */
+    return 0;
+}
+
diff --git a/cfn.c b/cfn.c
new file mode 100644
index 0000000..ad6776e
--- /dev/null
+++ b/cfn.c
@@ -0,0 +1,25 @@
+#include "cat.h"
+
+/* Function opens and writes the contents of a named file to stdout;
+ * effectively a wrapper around cfd() */
+int cfn(const char *fn, void *buf) {
+    int fd;
+
+    /* Open the file to get a read-only file descriptor */
+    if ((fd = open(fn, O_RDONLY)) == -1) {
+        perror(__FUNCTION__);
+        return -1;
+    }
+
+    /* Pass the opened descriptor to cfd() to read it; we keep going even if
+     * there are problems, because we need the descriptor closed even if we
+     * couldn't read it */
+    cfd(fd, buf);
+
+    /* Close the descriptor, since we should now be done with it */
+    if (close(fd) == -1) {
+        perror(__FUNCTION__);
+        return -1;
+    }
+}
+
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..620cc41
--- /dev/null
+++ b/main.c
@@ -0,0 +1,55 @@
+#include "cat.h"
+
+/* Main function */
+int main(int argc, const char *argv[]) {
+    int exv, i;
+    void *buf;
+
+    /* Exit value begins by assuming success */
+    exv = EXIT_SUCCESS;
+
+    /* Allocate a buffer with the prescribed size, or bail out */
+    if ((buf = malloc(BUFLEN)) == NULL) {
+        perror(__FUNCTION__);
+        exit(EXIT_FAILURE);
+    }
+
+    /* If there's at least one argument, we'll attempt to read from all the
+     * files named; if one of them doesn't work, we'll flag an error but will
+     * proceed */
+    if (argc > 1) {
+
+        /* Note we start at i = 1, not i = 0; the first element of argv is the
+         * command itself, not like in Perl */
+        for (i = 1 ; i < argc ; i++) {
+
+            /* If the filename is the special case of -, we emit stdin */
+            if (strncmp(argv[i], "-", 1) == 0) {
+                if (cfd(0, buf) == -1) {
+                    exv = EXIT_FAILURE;
+                }
+
+            /* Otherwise, we emit the file by name */
+            } else {
+                if (cfn(argv[i], buf) == -1) {
+                    exv = EXIT_FAILURE;
+                }
+            }
+        }
+
+    /* If there were no arguments, we assume the user wants us to read from
+     * stdin, which should already be opened */
+    } else {
+        if (cfd(0, buf) == -1) {
+            exv = EXIT_FAILURE;
+        }
+    }
+
+    /* Free the allocated buffer */
+    free(buf);
+    buf = NULL;
+
+    /* Done, exit appropriately */
+    exit(exv);
+}
+