[a-z] Specifies all characters a through z[a,z] or
[az]Specifies characters a or zSpace Acts as a delimiter between two wordsSpecial characters are very useful when you’re creating shell scripts, but if
you inadvertently use a special character as part of a variable name or string,
your program behaves incorrectly. As you learn in later parts of this chapter,
you can use one of the special characters in a string if you precede it with an
escape character (\, or backslash) to indicate that it isn’t being used as a
special character and shouldn’t be treated as such by the program.
A few special characters deserve special note: double quotes (”),single quotes
(’), backslash (), and backtick (`), all of which are discussed in the
following sections.
Using Double Quotes to Resolve Variables in Strings with
Embedded Spaces
If a string contains embedded spaces, you can enclose the string in double
quotes (”) so that the shell interprets the whole string as one entity instead of
as more than one.
For example, if you assigned the value abc def (abc followed by one
space, followed by def) to a variable called x in a shell program as follows,
you would get an error because the shell would try to execute def as a
separate command:
Command Environmentx=abc def pdksh and bashset x = adb deftcshThe shell executes the string as a single command if you surround the string
in double quotes, as follows:
Command Environmentx=“abc def” pdksh and bash