Blinking output

Gins · 07-22-2006, 01:57 PM

The following program doesn't work. I just get a blinking window. What is the problem? Your help is appreciated.
----------------------------------------------------------------

#!/bin/bash

x=0
while [ "$x" -lt 10 ] ; # this is loop1
do
y="$x"
while [ "$y" -ge 0 ] ; # this is loop2
do
echo "$y \c"
y=´echo "$y - 1" | bc´
done
echo
x=´echo "$x + 1" | bc´
done
--------------------------------------

The expected output of the above program is as follows:

0
1 0
2 1 0
3 2 1 0
4 3 2 1 0
5 4 3 2 1 0
6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
8 7 6 5 4 3 2 1 0
9 8 7 6 5 4 3 2 1 0

---------------------------------------------------------------------------
[ I just get a blinking window and I can't copy and past here. Something with the line 15.]

paulsm4 · 07-22-2006, 02:24 PM

Code:

#!/bin/bash

x=0
while [ $x -lt 10 ]; do
  y=$x
  while [ $y -ge 0 ]; do
    echo -n "$y"
    y=`expr $y - 1`
  done
  echo
  x=`expr $x + 1`
done
echo "Done."

Quote:

0
10
210
3210
43210
543210
6543210
76543210
876543210
9876543210
Done.

'Hope that helps .. PSM

PS:
Please start using "[code]" tags!

Gins · 07-22-2006, 04:17 PM

Thanks paulsm4 for the reply. You are very clever at scripting; I am not flattering you. I wish I could write scripts like you.

I must ask some questions.
x=0 [ Here we initialize the variable x. So it is initialized to 0.]

y=$x [ Here we initialíze the the variable y to x. Obviously x too is a variable.]

echo -n "$y"
y=`expr $y - 1` [ These two lines creates the vertical line.]

echo
x=`expr $x + 1` [ This creates the horizontal lines.]

Please tell me if I understood incorrectly. I have a limited knowledge of scripting.

paulsm4 · 07-22-2006, 04:26 PM

Hi -

Quote:

I must ask some questions.

x=0 [ Here we initialize the variable x. So it is initialized to 0.]
Yes, exactly right!

y=$x [ Here we initialíze the the variable y to x. Obviously x too is a variable.]
Yes again

echo -n "$y"
y=`expr $y - 1` [ These two lines creates the vertical line.]
No. I would prefer to say:
a) the first line displays "y" (without writing a newline)
b) the second line decrements "y"
...

Thank you for the kind words, and I hope that helps .. PSM

PS:
You'll note that I *didn't* leave a space between the numbers.
This is easily accomplished. You can either put a space in "echo" (as you did above), or you can use a tool like "awk" (which permits more sophisticated, "printf-sytle" formatting).

Gins · 07-22-2006, 04:34 PM

Thanks paulsm again for taking time to reply me.

echo -n "$y" [ What is the use of ' -n ' here?]

Because echo is a command to show some texts. Please read the following. It didn't make any difference when I inserted ' -n ' .

-------------------------
[nissanka@c83-250-110-112 ~]$ echo paulsm
paulsm
[nissanka@c83-250-110-112 ~]$

[nissanka@c83-250-110-112 ~]$ echo -n paulsm
paulsm[nissanka@c83-250-110-112 ~]$

paulsm4 · 07-22-2006, 11:15 PM

Try executing the above script with - and without - "echo -n" and compare what happens ;-)

Gins · 07-23-2006, 11:46 AM

Paulsm4

It doesn't work when I altered it. Please read the following:

#!/bin/bash

x=0
while [ $x -lt 10 ]; do
y=$x
while [ $y -ge 0 ]; do
echo n "$y"
y=`expr $y - 1`
done
echo
x=`expr $x + 1`
done
echo "Done

n 0

n 1
n 0

n 2
n 1
n 0

n 3
n 2
n 1
n 0

n 4
n 3
n 2
n 1
n 0

n 5
n 4
n 3
n 2
n 1
n 0

n 6
n 5
n 4
n 3
n 2
n 1
n 0

n 7
n 6
n 5
n 4
n 3
n 2
n 1
n 0

n 8
n 7
n 6
n 5
n 4
n 3
n 2
n 1
n 0

n 9
n 8
n 7
n 6
n 5
n 4
n 3
n 2
n 1
n 0
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

#!/bin/bash

x=0
while [ $x -lt 10 ]; do
y=$x
while [ $y -ge 0 ]; do
echo "$y"
y=`expr $y - 1`
done
echo
x=`expr $x + 1`
done
echo "Done."

[nissanka@c83-250-110-112 ~]$ ./unwanted20
0

1
0

2
1
0

3
2
1
0

4
3
2
1
0

5
4
3
2
1
0

6
5
4
3
2
1
0

7
6
5
4
3
2
1
0

8
7
6
5
4
3
2
1
0

9
8
7
6
5
4
3
2
1
0

[Simply speaking -n stops creating new lines.]

Gins · 07-23-2006, 03:58 PM

I still can't fathom out how this right-angled triangle forms.I understand all the codes and what they are doing.

Are you able to shed some light on this? I know it is a tall order to explain these things in an on line forum.

paulsm4 · 07-23-2006, 04:04 PM

Please cut/paste this script:

Code:

#!/bin/bash
x=0
while [ $x -lt 10 ]; do
  y=$x
  while [ $y -ge 0 ]; do
    echo -n "$y"
    y=`expr $y - 1`
  done
  echo
  x=`expr $x + 1`
done

QUESTION: Now execute it.
Does it produce this output?

Quote:

0
10
210
3210
43210
543210
6543210
76543210
876543210
9876543210
<= I HOPE THE ANSWER IS "YES"

Now remove the "-n" and re-run the script:

Code:

#!/bin/bash
x=0
while [ $x -lt 10 ]; do
  y=$x
  while [ $y -ge 0 ]; do
    echo "$y"
    y=`expr $y - 1`
  done
  echo
  x=`expr $x + 1`
done

The output from this version looks a lot like your output above, doesn't it?

Try this:

Quote:

man echo
<= WHAT DOES THE "MAN" PAGE SAY ABOUT "-n"

Finally, let's consider an approach that doesn't involve "echo -n" at all:

Code:

#!/bin/bash
X=0
while [ $X -lt 10 ]; do
  Y=$X
  S=""
  while [ $Y -ge 0 ]; do
    S="$S $Y"
    Y=`expr $Y - 1`
  done
  echo $S
  X=`expr $X + 1`
done

Quote:

0
1 0
2 1 0
3 2 1 0
4 3 2 1 0
5 4 3 2 1 0
6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
8 7 6 5 4 3 2 1 0
9 8 7 6 5 4 3 2 1 0

Does that help?

PS:
Code blocks are Good. Please start using code blocks.

PPS:
Please cut/paste this one final example and try it out:

Code:

#!/bin/bash
X=0
while [ $X -lt 10 ]; do
  Y=$X
  S=""
  while [ $Y -ge 0 ]; do
    S="$S -- $Y"
    Y=`expr $Y - 1`
  done
  echo $S
  X=`expr $X + 1`
done

Does this help explain "the right angled triangle" question?????

Gins · 07-23-2006, 04:42 PM

Paulsm4
Thanks for taking time to give me a excellent lengthy reply. Now it is too late here. I am a bit tired because I trained today. As a matter of fact I am training 3 times a week at a gym. I must sleep now.

I will attend this tomorrow. So please keep a good watch on this thread.
Are you based in the USA? If you are in the USA, it is not too late for you.

konsolebox · 07-23-2006, 06:49 PM

Quote:

Originally Posted by Gins

The expected output of the above program is as follows:

0
1 0
2 1 0
3 2 1 0
4 3 2 1 0
5 4 3 2 1 0
6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
8 7 6 5 4 3 2 1 0
9 8 7 6 5 4 3 2 1 0

here's a simpler approach. please try it.

Code:

#!/bin/bash

for ((a = 0; a <= 9; a++)); do
	echo "$a $b"
	b="$a $b"
done

OR

Code:

#!/bin/bash

MAXNUMBER=9

for ((a = 0; a <= MAXNUMBER; a++)); do
	b=$a
	until [[ $b < 0 ]]; do
		echo -n "$b "
		(( b-- ))
	done
	echo
done

Gins · 07-24-2006, 02:47 PM

I thank both paulsm4 and konsolebox for the help. I am very proud of your knowledge of programming.

Our friend konsolebox has done the same programme in two different ways. Oh! What a talent!
The way konsolebox has made programmes reminds me of the codes use in C++ programming. I worked with C++ programming some years ago. One of his programmes has only 4 lines; it works fine.

The following programme from paulsm4 works fine too.
#!/bin/bash
x=0
while [ $x -lt 10 ]; do
y=$x
while [ $y -ge 0 ]; do
echo "$y"
y=`expr $y - 1`
done
echo
x=`expr $x + 1`
done

So if you know all the pros and cons of programming, you could write a same programme in many different ways. I wish I could write programmes like paulsm4 and konsolebox.