COMP421
Unix Environment for Programmers
Lecture 06: Shell scripts continues_______________________________

Jeff Wiegley, Ph.D.
Computer Science
jeffw@csun.edu

09/12/2005

1

Shell substitution:____________________________________

• Before executing any command the shell first performs “substitution”.
• Substitution can be very confusing.

2

Variables are substituted____________________________

The presence of an string that begins with $ is considered a variable and the contents of the variable are substituted for the name.

This is confusing because somethings won’t work as expected.

actual yields... grep hello there targetfile which will search for “hello” in the two files there and targetfile.

grep "$myphrase" targetfile would fix this problem

3