Add argument handling and a README for mygrep

.gitignore

@@ -1 +1,2 @@
 .vscode/
+*.out

mygrep/README.md

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+# mygrep
+
+A reduced variation of the Unix-command `grep`.
+It reads in several files and prints all lines containing a keyword.
+
+`   SYNOPSIS
+    mygrep [-i] [-o outfile] keyword [file...] `
+
+The program `mygrep` reads files line by line and for each line checks whether it contains the search
+term keyword. The line is printed if it contains the keyword, otherwise it is not printed.
+The program accepts lines of any length.
+
+If one or multiple input files are specified (given as positional arguments after keyword), then mygrep 
+reads each of them in the order they are given. If no input file is specified, the program reads from
+`stdin`.
+
+If the option `-o` is given, the output is written to the specified file (outfile). Otherwise, the output is
+written to `stdout`.
+
+If the option `-i` is given, the program does not differentiate between lower and upper case letters, i.e.
+the search for the keyword in a line is case insensitive.
+
+**Note: The description is from the task I got from TU.**

mygrep/mygrep.c

@@ -1,5 +1,68 @@
 #include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include "mygrep.h"
 
-void main() {
+void main(int argc, char *argv[]) {
-    printf("Hello, World!");
+    check_opts_number(argc, argv);
+
+    int iflag = 0;
+    char *ofile = NULL;
+    char *keyword = NULL;
+    char *filename = NULL;
+    int c;
+
+    while((c = getopt(argc, argv, "io:h")) != -1) {
+        switch(c) {
+            case 'i':
+                iflag = 1;
+                break;
+            case 'o':
+                ofile = optarg;
+                break;
+            case 'h':
+                print_usage();
+                break;
+            case '?':
+                print_usage();
+                exit(EXIT_FAILURE);
+            default:
+                abort();
+        }
+    }
+
+    if(argv[optind] == NULL) {
+        printf("Mandatory argument 'keyword' missing.\n");
+        print_usage();
+        exit(EXIT_FAILURE);
+    } else {
+        keyword = argv[optind];
+        filename = argv[optind + 1];
+    }
+
+    if(filename == NULL) {
+        check_for_string("test", keyword);
+    }
+
+    exit(EXIT_SUCCESS);
+}
+
+void print_usage() {
+    printf("mygrep [-i] [-o outfile] keyword [file...]\n");
+}
+
+void check_opts_number(int argc, char *argv[]) {
+    if(argc <= 1) {
+        fprintf(stderr, "At least one argument expected.\n");
+        print_usage();
+        exit(EXIT_FAILURE);
+    } else if(argc > 6) {
+        fprintf(stderr, "Too many arguments supplied.\n");
+        print_usage();
+        exit(EXIT_FAILURE);
+    }
+}
+
+void check_for_string(char *to_check, char *to_find) {
+    printf("Not implemented. This function will search for the substring %s in the string %s.\n", to_find, to_check);
 }

mygrep/mygrep.h

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+#ifndef MYGREP_HEADER
+#define MYGREP_HEADER
+
+void print_usage();
+void check_opts_number(int argc, char *argv[]);
+void check_for_string(char *to_check, char *to_find);
+
+#endif