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Quoting
Now that we've seen how many ways the shell can perform expansions, it's time to learn how we can control it. Take for example:
[me@linuxbox ~]$ echo this is a
this is a test
test
[me@linuxbox ~]$ echo this is a
this is a test
or:
[me@linuxbox ~]$ echo The total is $100.00
The total is 00.00
[me@linuxbox ~]$ echo The total is $100.00
The total is 00.00
In the first example, word-splitting by the shell removed extra whitespace from the echo command's list of arguments. In the second example, parameter expansion substituted an empty string for the value of “$1” because it was an undefined variable. The shell pro- vides a mechanism called quoting to selectively suppress unwanted expansions.