-bash-4.3$ ls -l *.txt
-rw-r--r-- 1 mikec faculty 5 Feb  6 17:18 abcd.txt
-rw-r--r-- 1 mikec faculty 5 Feb  6 17:23 cdef.txt
-r--r--r-- 1 mikec faculty 0 Feb  6 17:08 nowrite.txt   [notice: no write permission]
-bash-4.3$ cat abcd.txt 
abcd
-bash-4.3$ cat cdef.txt 
cdef
-bash-4.3$ ./counts abcd.txt 
Code	Char	Count
----	----	-----
 10	LF	    1
 97	a	    1
 98	b	    1
 99	c	    1
100	d	    1
		-----
Total		    5
-bash-4.3$ ./counts abcd.txt cdef.txt 
Code	Char	Count
----	----	-----
 10	LF	    2
 97	a	    1
 98	b	    1
 99	c	    2
100	d	    2
101	e	    1
102	f	    1
		-----
Total		   10
-bash-4.3$ ./counts abcd.txt cdef.txt -o results.txt
-bash-4.3$ cat results.txt 
Code	Char	Count
----	----	-----
 10	LF	    2
 97	a	    1
 98	b	    1
 99	c	    2
100	d	    2
101	e	    1
102	f	    1
		-----
Total		   10
-bash-4.3$ ./counts -o interactive.txt
Typing now ...
^d next line
-bash-4.3$ cat interactive.txt 
Code	Char	Count
----	----	-----
 10	LF	    2
 32	SPC	    4
 46	.	    3
 84	T	    1
 94	^	    1
100	d	    1
101	e	    2
103	g	    1
105	i	    2
108	l	    1
110	n	    4
111	o	    1
112	p	    1
116	t	    1
119	w	    1
120	x	    1
121	y	    1
		-----
Total		   28
-bash-4.3$ ./counts MSG1.txt
bad file: MSG1.txt
-bash-4.3$ ./counts msg1.txt MSG2.txt
bad file: msg1.txt
-bash-4.3$ ./counts -o nowrite.txt 
bad file: nowrite.txt
-bash-4.3$ ./counts -x results.txt
bad option: -x
-bash-4.3$ ./counts -o
missing output file
-bash-4.3$ ./counts -ofilename
missing output file