printout sending control codes to the console?

[Konstantin Svist]

I have a script which prints out some data to the terminal, which I keep
in a screen session.
Often times I see indecipherable characters printed out and the output
freezes - I'm guessing some control code is being triggered from the
printout.
Is there a way to prevent this?

[Jerry Feldman]

On 02/24/2009 07:53 PM, Konstantin Svist wrote:
> I have a script which prints out some data to the terminal, which I keep
> in a screen session.
> Often times I see indecipherable characters printed out and the output
> freezes - I'm guessing some control code is being triggered from the
> printout.
> Is there a way to prevent this?

ASCII contains a number of control codes. One of these is XOFF (stop 
output or control-S) and another is XON (resume output or control Q). 
Basically the C function isprint(3) tests if a character is printable 
(in C). I'm sure there are similar functions available to Perl and other 
scripting languages. Or you can simply test the value of a character. If 
it is < 0x20 it is a control character.

[Mikkel]

Jerry Feldman wrote:
> On 02/24/2009 07:53 PM, Konstantin Svist wrote:
> > I have a script which prints out some data to the terminal, which I keep
> > in a screen session.
> > Often times I see indecipherable characters printed out and the output
> > freezes - I'm guessing some control code is being triggered from the
> > printout.
> > Is there a way to prevent this?
>
> ASCII contains a number of control codes. One of these is XOFF (stop
> output or control-S) and another is XON (resume output or control Q).
> Basically the C function isprint(3) tests if a character is printable
> (in C). I'm sure there are similar functions available to Perl and other
> scripting languages. Or you can simply test the value of a character. If
> it is < 0x20 it is a control character.

You do not want to stop all control characters - you will need 0x0A
and 0x0D. You also need to watch out for are characters above 0x7F
as they will be special characters (font dependent).

Dependent on the terminal emulation, you may also have an alternate
font command. (0x0B?) This can produce interesting results.

Mikkel

[James Wilkinson]

Konstantin Svist wrote:
> I have a script which prints out some data to the terminal, which I keep
> in a screen session.
> Often times I see indecipherable characters printed out and the output
> freezes - I'm guessing some control code is being triggered from the
> printout.
> Is there a way to prevent this?

Pipe it through cat -vet?

(Strictly, only cat -v is needed. -e adds a $ at the end of each line
and -t prints tabs as ^I. And if you have -e, you don’t need -v for Gnu
cat. This isn’t true with other cats, and “cat -vet” is easy to
remember!)

James