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Managing Variable Attributes with typeset - Part I

As your shell scripts become more diverse and complex, there will be times when you will want or need to manipulate the attributes of a script's variables.  The typeset command allows you to set, unset, and display these attributes.  The syntax for typeset is:

typeset -option(s) [variable_name[=value]]...

A minus sign before the option list sets the attributes for the variable list.  Variable attributes can be unset by replacing the minus sign with a plus sign:

typeset +option(s) [variable_name[=value]]...

Notice that the variable name and value are optional arguments.  If these are not included after specifying one or more attributes, the variables having the specified attribute(s) and their values will be displayed when the minus sign is used:

$ typeset -l
animal1=dog
animal2=cat
animal3=duck
$

When a plus sign is used, only the variable names are displayed:

$ typeset +l
animal1
animal2
animal3
$

The option "l" is used to set, unset, and display (as seen above) the lowercase attribute:

$ typeset -l answer
$ answer=Y
$ print $answer
y
$

In this example, the lowercase attribute is first set for the variable answer.  No initial value is assigned to answer.  The second statement assigns the uppercase letter "Y" to answer, and as you can see, the value is automatically converted to lowercase.  To set the uppercase attribute for a variable, the -u option is used:

$ print $answer
y
$ typeset -u answer
$ print $answer
Y
$  

Read the NEXT article in this series - Managing Variable Attributes with typeset - Part II