typeset (Learning the Korn Shell, 2nd Edition)

function afunc { typeset diffvar samevar=funcvalue diffvar=funcvalue print "samevar is $samevar" print "diffvar is $diffvar" } samevar=globvalue diffvar=globvalue print "samevar is $samevar" print "diffvar is $diffvar" afunc print "samevar is $samevar" print "diffvar is $diffvar"

6.5.2. String Formatting Options

Now let's look at the various options to typeset. Table 6-6 lists the string formatting options; the first three take an optional numeric argument.

Table 6-6. Typeset string formatting options

Option	Operation
`-L``n`	Left-justify. Remove leading spaces; if n is given, fill with spaces or truncate on right to length n.
`-R``n`	Right-justify. Remove trailing spaces; if n is given, fill with spaces or truncate on left to length n.
`-Z``n`	If used with `-R`, add leading 0's instead of spaces if needed. If used with `-L`, strips leading 0's. By itself, acts the same as `-RZ`.
`-l`	Convert letters to lowercase.
`-u`	Convert letters to uppercase.

Here are a few simple examples. Assume that the variable alpha is assigned the letters of the alphabet, in alternating case, surrounded by three spaces on each side:

alpha="   aBcDeFgHiJkLmNoPqRsTuVwXyZ   "

Table 6-7 shows some typeset statements and their resulting values (assuming that each of the statements are run "independently").

Table 6-7. Examples of typeset string formatting options

Statement	Value of v
`typeset -L v=$alpha`	`"aBcDeFgHiJkLmNoPqRsTuVwXyZ "`
`typeset -L10 v=$alpha`	`"aBcDeFgHiJ"`
`typeset -R v=$alpha`	" aBcDeFgHiJkLmNoPqRsTuVwXyZ"
`typeset -R16 v=$alpha`	`"kLmNoPqRsTuVwXyZ"`
`typeset -l v=$alpha`	" abcdefghijklmnopqrstuvwxyz "
`typeset -uR5 v=$alpha`	`"VWXYZ"`
`typeset -Z8 v="123.50"`	`"00123.50"`

When you run typeset on an existing variable, its effect is cumulative with whatever typesets may have been used previously. This has the obvious exceptions:

A typeset -u undoes a typeset -l, and vice versa.
A typeset -R undoes a typeset -L, and vice versa.
You may not combine typeset -l and typeset -u with some of the numeric attributes, such as typeset -E. Note, though, that typeset -ui creates unsigned integers.
typeset -A and typeset -n (associative array and nameref, respectively) are not cumulative.

You can turn off typeset options explicitly by typing typeset +o, where o is the option you turned on before. Of course, it is hard to imagine scenarios where you would want to turn multiple typeset formatting options on and off over and over again; you usually set a typeset option on a given variable only once.

An obvious application for the -L and -R options is one in which you need fixed-width output. The most ubiquitous source of fixed-width output in the Unix system is reflected in Task 6-3.

Task 6-3

Pretend that ls doesn't do multicolumn output; write a shell script that does it.

For the sake of simplicity, we'll assume further that our version of Unix is an ancient one, in which filenames are limited to 14 characters.[87]

[87] We don't know of any modern Unix systems that still have this restriction. But applying it here considerably simplifies the programming problem.

Our solution to this task relies on many of the concepts we have seen earlier in this chapter. It also relies on the fact that set -A (for constructing arrays) can be combined with command substitution in an interesting way: each word (separated by spaces, TABs, or newlines) becomes an element of the array. For example, if the file bob contains 50 words, the array fred has 50 elements after the statement:

set -A fred $(< bob)

Our strategy is to get the names of all files in the given directory into an array variable. We use an arithmetic for loop as we saw earlier in this chapter, to get each filename into a variable whose length has been set to 14. We print that variable in five-column format, with two spaces between each column (for a total of 80 columns), using a counter to keep track of columns. Here is the code:

set -A filenames $(ls $1)
typeset -L14 fname
let numcols=5

for ((count = 0; count < ${#filenames[*]} ; count++)); do
    fname=${filenames[count]}
    print -rn "$fname  "
    if (( (count+1) % numcols == 0 )); then
        print           # newline
    fi
done

if (( count % numcols != 0 )); then
    print
fi

The first line sets up the array filenames to contain all the files in the directory given by the first argument (the current directory by default). The typeset statement sets up the variable fname to have a fixed width of 14 characters. The next line initializes numcols to the number of columns per line.

The arithmetic for loop iterates once for every element in filenames. In the body of the loop, the first line assigns the next array element to the fixed-width variable. The print statement prints the latter followed by two spaces; the -n option suppresses print's final newline.

Then there is the if statement, which determines when to start the next line. It checks the remainder of count + 1 divided by $numcols -- remember that dollar signs aren't necessary within a $((...)) construct -- and if the result is 0, it's time to output a newline via a print statement without arguments. Notice that even though $count increases by 1 with every iteration of the loop, the remainder goes through a cycle of 1, 2, 3, 4, 0, 1, 2, 3, 4, 0, ...

After the loop, an if construct outputs a final newline if necessary, i.e., if the if within the loop didn't just do it.

We can also use typeset options to clean up the code for our dosmv script (Task 5-3), which translates filenames in a given directory from MS-DOS to Unix format. The code for the script is:

for filename in ${1:+$1/}* ; do
    newfilename=$(print $filename | tr '[A-Z]' '[a-z]')
    newfilename=${newfilename%.}
    # subtlety: quote value of $newfilename to do string comparison,
    # not regular expression match
    if [[ $filename != "$newfilename" ]]; then
        print "$filename -> $newfilename"
        mv $filename $newfilename
    fi
done

We can replace the call to tr in the for loop with one to typeset -l before the loop:

typeset -l newfilename
for filename in ${1:+$1/}* ; do
    newfilename=${filename%.}
    # subtlety: quote value of $newfilename to do string comparison,
    # not regular expression match
    if [[ $filename != "$newfilename" ]]; then
        print "$filename -> $newfilename"
        mv $filename $newfilename
    fi
done

This way, the translation to lowercase letters is done automatically each time a value is assigned to newfilename. Not only is this code cleaner, but it is also more efficient, because the extra processes created by tr and command substitution are eliminated.

Option

Operation

-A

Create an associative array.

-En

Represent the variable internally as a double-precision floating-point number; improves the efficiency of floating-point arithmetic. If n is given, it is the number of significant figures to use in output. Large numbers print in scientific notation: [-]d.ddde±dd. Smaller numbers print in regular notation: [-]ddd.ddd.

-Fn

Represent the variable internally as a double-precision floating-point number; improves the efficiency of floating-point arithmetic. If n is given, it is the number of decimal places to use in output. All values print in regular notation: [-]ddd.ddd.

-H

On non-Unix systems, Unix-style filenames are converted into the format appropriate for the local system.

-in

Represent the variable internally as an integer; improves the efficiency of integer arithmetic. If n is given, it is the base used for output. The default base is 10.

-n

Create a nameref variable (see Chapter 4).

-p

When used by itself, prints typeset statements that describe the attributes of each of the shell's variables that have attributes set. With additional options, only prints those variables that have the corresponding attribute set. Intended for dumping the shell's state into a file that can later be sourced by a different shell to recreate the original shell's state.

-r

Make the variable read-only: forbid assignment to it and disallow it from being unset. The built-in command readonly does the same thing, but readonly cannot be used for local variables.

-t

"Tags" the variable. The list of tagged variables is available from typeset +t. This option is obsolete.

-uin

Represent the variable internally as an unsigned integer. This is discussed further in Appendix B. If n is given, it is the base used for output. The default base is 10.[88]

-x

This does the same thing as the export command, but export cannot be used for local variables.

-f

Refer to function names only; see Section 6.5.4, later in this chapter.

Option

Operation

-f

With no arguments, prints all function definitions.

-f fname

Prints the definition of function fname.

+f

Prints all function names.

-ft

Turns on trace mode for named function(s). (Chapter 9)

+ft

Turns off trace mode for named function(s). (Chapter 9)

-fu

Defines given name(s) as autoloaded function(s). (Chapter 4)

export HISTFILE integer TMOUT export FCEDIT export _AST_FEATURES export TERM HISTEDIT PS2 PS3 integer PPID export MAIL export LOGNAME export EXINIT integer LINENO export PATH integer HISTCMD export _ export OLDPWD export PWD float precision 3 SECONDS export SHELL integer RANDOM export HOME export VISUAL export MANPATH export EDITOR export ENV export HISTSIZE export USER export LANG export MORE integer OPTIND integer MAILCHECK export CDPATH readonly namespace .sh

typeset -x HISTFILE typeset -i TMOUT typeset -x FCEDIT typeset -x _AST_FEATURES typeset -x TERM typeset -x ASIS_DIR typeset HISTEDIT typeset PS2 typeset PS3 typeset -i PPID typeset -x MAIL typeset -x LOGNAME typeset -x EXINIT typeset -i LINENO typeset -x PATH typeset -i HISTCMD typeset -x _ typeset -x OLDPWD typeset -x PWD typeset -F 3 SECONDS typeset -x SHELL typeset -i RANDOM typeset -x HOME typeset -x VISUAL typeset -x MANPATH typeset -x EDITOR typeset -x ENV typeset -x HISTSIZE typeset -x USER typeset -x LANG typeset -x MORE typeset -i OPTIND typeset -i MAILCHECK typeset -x CDPATH typeset -r .sh

6.5. typeset

6.5.1. Local Variables in Functions

Figure 6-1. Local variables in functions

6.5.2. String Formatting Options

Table 6-6. Typeset string formatting options

Table 6-7. Examples of typeset string formatting options

Task 6-3

6.5.3. Type and Attribute Options

Table 6-8. Typeset type and attribute options

6.5.4. Function Options

Table 6-9. Typeset function options