# Screen input/output

It is possible to solicit input and display output in a
paragraph. To do simple output, use the display statement with a string
argument. To do simple input, embed the desired prompt within `>` (double angle brackets).
For example, the line `display >` prompts `Enter name>` and then prints the name.

The paragraph input function has many forms. All of them
get input from one of several sources, and substitute that input in
place of the original function on the paragraph line.

The syntax
for screen input and output:

```
<<cnumber>>
<<inumber, prompt.text>>
<<f(file.name,item.name{,attribute{,value}}),prompt.text>>
<<{options}{,@([x,y|bell|clr])},prompt.text{,mask}>>
```
To get input from the keyboard, use the last form. The
parameters include:

| cnumber | c, followed by a number option, indicates that the input function should be replaced by the nth parameter on the original TCL line executing the paragraph. The first parameter returns the paragraph name. | |
| --- | --- | --- |
| inumber | i, followed by a number, is identical to the c form, except that if the parameter is null, then the user is prompted for the desired input. | |
| f(file.name, item.name) | Gets input from a file. If the item or file is not found, then the user is prompted with the specified prompt. | |
| [] | Separates elements. | |
| \| | Specifies either/or. | |
| options | a | Prompts the user even if the data is already present. If a duplicate prompt displays twice in a paragraph, the user is not prompted more than once for the input. Instead, all further uses of the same prompt remembers the original input and returns the result without user intervention. |
| r | Causes the input statement to repeat (r) until the input is null. The final result contains every previous input separated by spaces. This is useful for creating item lists. | |
After the options, the user may specify a direct cursor
address or several predefined constants.

Finally, the input statement requires a prompt string followed by an
optional mask. The mask has the same syntax as that used by the BASIC matches function.

Typing quit at
any paragraph input prompt terminates the paragraph and returns to
TCL.

## Parameter Manipulation

Unlike standard macros,
the parameters to the original TCL command line executing a paragraph
are not directly passed to the first command. Instead, they are placed
in a buffer for the paragraph programmer to access individually. The `>`. To access the second parameter, use `>`.

The syntax for parameter manipulation:

```
<<cnumber>>
<<Inumber,prompt.text>>
```
The parameters include:

| cnumber | c, followed by a number, indicates that the input function should be replaced by the nth parameter on the original TCL line executing the paragraph. The first parameter returns the paragraph name. |
| --- | --- |
| inumber | i, followed by a number, is identical to the c form, except that if the parameter is null, then the user is prompted for the desired input. |
| prompt.text | Displays text that requires user input. |

---
Source: https://d3codex.com/tcl/screen-input-output/ - part of the D3Codex reference.