STDOUT - Overwriting previous line

[Natti]

Hello,
I am trying to update the STDOUT dynamically.
For eg. I am trying to display a counter whose value should get updated int he same place,

#!/usr/bin/perl

$val = 10;
for ($i=0;$i<=$val; $i+) {
print "$val\n";
}
would print
0
1
2
3
4
5
6
7
8
9
10

What I am looking at is a clock like feature where the earlier output is overwritten by the current value of val.

[miller]

Read this thread for discussion on flushing STDOUT
http://www.thescripts.com/forum/thread603712.html

As far as overwriting the same line, you simply need a carriage return: "\r". You can read about them in the O'Reilly Camel book under "carriage returns".

 
#!/usr/bin/perl
 
use strict;
 
local $| = 1;
 
my $val = 10;
for (my $i=0; $i<=$val; $i++) {
    print "\r$val";
}
 

[docsnyder]

Consider a user wants to write to the same line, where subsequent lines could get shorter. The example (according to youre approach):

my $val = 0;
for (my $i=10; $i>$val; $i--) {
    print "\r$i";
    sleep(1);
}

would print

10
90
80
...
 

A solution to erase everything written before would be:

my $val = 0;
my $n   = 0;
for (my $i=10; $i>$val; $i--) {
    printf("\r%s\r$i", " " x $n);
    $n = length($i."");
}

Greetz, Doc