Added silent mode and a manual page

Makefile

@@ -1,5 +1,23 @@
-subnetcalc: subnetcalc.c
+CC=gcc
-	gcc -std=c99 -Wall -pedantic subnetcalc.c -lm -o subnetcalc
+CFLAGS=-Wall -pedantic -std=c99
+LIBS=-lm
+OBJS=subnetcalc.o
+BINDIR=/usr/local/bin
+MANDIR=/usr/share/man/man1
 
-clean: subnetcalc
+subnetcalc: $(OBJS)
-	rm subnetcalc
+	$(CC) -o subnetcalc $(OBJS) $(LIBS)
+
+subnetcalc: subnetcalc.c
+
+install: subnetcalc subnetcalc.1
+	gzip -c subnetcalc.1 > subnetcalc.1.gz
+	install -g root -o root -m 0644 subnetcalc.1.gz $(MANDIR)/
+	install -g root -o root -m 0755 subnetcalc $(BINDIR)/
+
+uninstall:
+	rm $(MANDIR)/subnetcalc.1.gz
+	rm $(BINDIR)/subnetcalc
+
+clean:
+	rm subnetcalc $(OBJS) subnetcalc.1.gz

README.md

@@ -1,4 +1,4 @@
-# subnetcalc #
+# subnetcalc
 A very simple subnet calculator written in C. It's nothing fancy at all,
 just a small project of mine to get me going with C.
 
@@ -16,3 +16,19 @@ You can also give the netmask to the program as an argument. For example:
     256 total addresses
     254 usable addresses for hosts
 
+Since version 1.0 it's also possible to run the program in silent mode
+accepting input in stdin. This is excellent for batch processing. But note that
+in this mode the program only calculates the total number of addresses.
+
+## Installation
+
+    make
+    sudo make install
+
+## Uninstalling
+
+    sudo make uninstall
+
+## Getting help
+
+    man subnetcalc

subnetcalc.1

@@ -0,0 +1,22 @@
+.TH SUBNETCALC 1 "OCTOBER 2020" "Version 1.0" "User Manuals"
+.SH NAME
+subnetcalc \- calculate the number of address in a subnet
+.SH SYNOPSIS
+.B subnetcalc \fR[netmask] [-s]
+.SH DESCRIPTION
+.B subnetcalc
+is a simple subnet calculator. The user provides a subnet to the program,
+either as a argument or interactivly. The program then calculates the total
+number of addresses and usable addresses in that subnet. It is also possible to
+do batch processing with \fB\-s\fR option.
+.SH OPTIONS
+.TP
+.B \-s
+Makes the program silent and accept input on stdin. In this mode, the program
+will only calculate the total number of addresses in the given netmask.
+.SH RETURN VALUES
+Upon error, 1 is returned. Otherwise, 0 is returned.
+.SH AUTHOR
+Jack-Benny Persson <jack-benny@cyberinfo.se>
+.SH "SEE ALSO"
+.BR bc (1)

subnetcalc.c

@@ -1,6 +1,7 @@
 /* A very simple subnet calculator in C, written by
  * Jack-Benny Persson (jack-benny@cyberinfo.se).
  * Released under GNU GPLv2.
+ * Version 1.0 (2020-10-09)
 */
 #include <stdio.h>
 #include <math.h>
@@ -15,7 +16,7 @@ void printHelp(char progname[]);
 
 int main(int argc, char *argv[])
 {
-    char input[3] = { 0 };
+    char input[4] = { 0 };
     int net;
 
     if (argc == 1) /* User didn't supply an argument, go interactive */
@@ -37,7 +38,23 @@ int main(int argc, char *argv[])
     }
     else if (argc == 2) /* User supplied exactly one argument */
     {
-        if (checkInput(argv[1]))
+        if ( strcmp("-s", argv[1]) == 0) /* User wants a silent batch */
+        {
+            while(fgets(input, sizeof(input), stdin) != NULL)
+            {
+                /* Check if netmask is numeric (and do conversion) */
+                if( checkInput(input) )
+                {
+                    printf("%ld\n", calcAddr(atoi(input)));
+                }
+                else
+                {
+                    printHelp(argv[0]);
+                    return 1;
+                }
+            }
+        }
+        else if (checkInput(argv[1]))
         {
             net = atoi(argv[1]);
             printAddr(net);
@@ -105,11 +122,16 @@ void printAddr(int netmask)
 
 void printHelp(char progname[])
 {
-    printf("Usage: %s [netmask]\n", progname);
+    printf("Usage: %s [netmask] [-s]\n", progname);
     printf("If the program is started without any arguments, "
-            "it's started in interactive mode.\n");
+            "it is started in interactive mode.\n"
-    printf("Optionally, a netmask can be supplied as a "
+            "Optionally, a netmask can be supplied as a "
-            "argument.\n");
+            "argument.\n"
-    printf("Examle: %s 24\n", progname);
+            "If the program is started with the -s option, "
+            "the program will silently accept input on stdin,\n"
+            "outputting the number of total address on stdout\n");
+    printf("\nExample: %s \n"
+           "Example: %s 24\n"
+           "Example: %s -s\n", progname, progname, progname);
 }