reading back characters from terminal

reading back characters from terminal

[Fekete Gabor]

hi,

is there a way to read back characters from the terminal (e.g. xterm).
i mean for example running xterm with bash and writing a program that
when run from the bash prompt could read an arbitrary text back from
the xterm window.
e.g.:

$ ls -al
total 16
drwxr-xr-x    4 x        users        4096 Jun 20 00:39 ./
drwxr-xr-x   21 x        users        4096 Aug 13 21:33 ../
drwxr-xr-x    2 x        users        4096 Jun 22 20:45 colors/
drwxr-xr-x    2 x        users        4096 Jun 14 20:06 plugin/
$ program
and then the "program" would read back the contents of the terminal, like
ten characters starting from the position row 5, line 7.

WITHOUT NCURSES!

anyone?

Re: reading back characters from terminal

[Glynn Clements]

Fekete Gabor wrote:

> is there a way to read back characters from the terminal (e.g. xterm).

No. There isn't even any guarantee that the characters are actually
stored anywhere. Certainly, hardcopy terminals don't store the text,
nor do graphics terminals (Tek4014 etc).

Even when the terminal (or emulator) does store the text, there isn't
any portable mechanim for reading it. For specific terminals, there
may be specific mechanims to obtain the data; e.g. for the Linux
console, you could read it from video memory, provided you had the
appropriate privileges.

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: reading back characters from terminal

[Fekete Gabor]

On Thu, 14 Aug 2003, Glynn Clements wrote:

> 
> Fekete Gabor wrote:
> 
> > is there a way to read back characters from the terminal (e.g. xterm).
> 
> No. There isn't even any guarantee that the characters are actually
> stored anywhere. Certainly, hardcopy terminals don't store the text,

sad.
anyway, thanks for the info!

Re: program killed

[Tony Clarke]

Sounds like your system was tight on memory and the Memory Manager 
thought your
program was a good one to kill to recoup some scarce memory.

Have a look in /mm/oom_kill.c to see how it figures out who to kill.

>Hi there,
>
>Can anyone give me some hints about why my program is killed by system? I am 
>now debugging a program but after it runs for a while, I got a message saying 
>"Program terminated with signal SIGKILL, Killed". What's the causes? 
>Memory? I am the only user since I disconnected the computer (64 MB RAM) to 
>the network.  Last night I also run my program on my laptop (256 MB RAM), it 
>worked well when I used a part of data set (image). With the whole data the 
>program also got killed. I checked the syslog and found "VM: kill the program 
>XXX". I used MALLOC_CHECK_ but there is no memory abuse. Any suggestion?
>
>Many thanks in advance.
>
>QingHua
>-
>To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
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>
>  
>



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program killed

[QingHua Wang]

Hi there,

Can anyone give me some hints about why my program is killed by system? I am 
now debugging a program but after it runs for a while, I got a message saying 
"Program terminated with signal SIGKILL, Killed". What's the causes? 
Memory? I am the only user since I disconnected the computer (64 MB RAM) to 
the network.  Last night I also run my program on my laptop (256 MB RAM), it 
worked well when I used a part of data set (image). With the whole data the 
program also got killed. I checked the syslog and found "VM: kill the program 
XXX". I used MALLOC_CHECK_ but there is no memory abuse. Any suggestion?

Many thanks in advance.

QingHua

Re: program killed

[Tony Clarke]

QingHua Wang wrote:

>Many thanks for your response. I searched the web and found some information.
>I gonna figue this out later as you suggested. Where can I find this file 
>/mm/oom_kill.c? I can not find it after searching the two computers. One is 
>installed with Mandrake 8.0 and another 9.1. Thanks.
>  
>

Have a look here.
http://linuxcompressed.sourceforge.net/vm24/oom_kill.html
http://www.kernel.org/pub/linux/kernel/people/marcelo/linux-2.4/mm/oom_kill.c

You'll need to have the kernel source code installed on the machine to 
view it. Usually
thats in /usr/src/linux/




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Re: program killed

[QingHua Wang]

Many thanks for your response. I searched the web and found some information.
I gonna figue this out later as you suggested. Where can I find this file 
/mm/oom_kill.c? I can not find it after searching the two computers. One is 
installed with Mandrake 8.0 and another 9.1. Thanks.

Re: reading back characters from terminal

[Fekete Gabor]

> 
> 
> On Thu, 14 Aug 2003, Glynn Clements wrote:
> 
> > 
> > Fekete Gabor wrote:
> > 
> > > is there a way to read back characters from the terminal (e.g. xterm).
> > 
> > No. There isn't even any guarantee that the characters are actually
> > stored anywhere. Certainly, hardcopy terminals don't store the text,
> 
one more question.

then why can I select text with the mouse both in xterm and on a text
console and then paste it somewhere?

Re: reading back characters from terminal

[Glynn Clements]

Fekete Gabor wrote:

> > > > is there a way to read back characters from the terminal (e.g. xterm).
> > > 
> > > No. There isn't even any guarantee that the characters are actually
> > > stored anywhere. Certainly, hardcopy terminals don't store the text,
> > 
> one more question.
> 
> then why can I select text with the mouse both in xterm and on a text
> console and then paste it somewhere?

Because both of those terminals *do* store the text somewhere. 
Unfortunately, exactly where they store it, and in what format, is
specific to the particular terminal.

[Actually, that's only half true for xterm. xterm emulates both a DEC
VT-220 and a Tektronix 4104; you can only paste the text from the
VT-220, not the 4104.]

Theoretically, you could go digging around in the xterm process'
memory, via /proc/<pid>/mem (although, if xterm is running as root,
you'll need root privilege). Or in the framebuffer memory for the
Linux console (again, probably needs root privilege). But that won't
work for a remote login (telnet, ssh, minicom etc).

Similarly, you might be able to get the text from an xterm by OCR'ing
a screen dump, provided that your program can access the X display,
that it can figure out which xterm it is talking to, and that the
xterm itself isn't obscured. But that would be a lot of work, and
wouldn't be particularly reliable.

-- 
Glynn Clements <glynn.clements@virgin.net>