1) In file ex1.txt, replace all occurrences
of character x with character z on 
lines 2, 3, and 4.

2) In file ex1.txt, replace all occurrences
of character x with character z on all lines 
except 2, 3, and 4.

3) In file ex1.txt, replace all occurrences
of character x with character z on all
lines that contain a character a

4) In file ex1.txt, replace all occurrences
of character x with character z on all
lines that do NOT contain a character a

5) In file ex1.txt, replace all occurrences
of character x with character z on 
lines 2, 3, and 4, BUT output only the affected
lines.

6) File ex4.txt contains the man page for wc.
From that file, extract only the sections with
the name, synopsis, and description.
Hint: you may need to use two commands.

7) In the file ex2.txt, on all lines that contain
the keyword Linux, replace (a) everything from the beginning
of the line to after the keyword Linux with the empty string
and (b) the keyword command and everything that follows with
a colon.

8) In the file ex2.txt, replace the ls that occurs
at the end of a line with the string "the ls command"

9) Can you do the same as in the question above
but for all commands and without specifying each
one explicitly?

10) In the file brackets.txt, replace all curly brackets '(' and ')'
with square brackets '[' and ']'