reverse number by twos

TimothyBrian · 10-25-2011, 12:39 AM

how to reverse the numbers sir and mam, see below.. thanks guys!

input file:
8360319029018040012
85951209030597537

output:
3806130992100804102
58592190305079357

hen770 · 10-25-2011, 01:06 AM

Explain yourself more.
Do you want the output to be as your post, or you want it to be reveresed?

TimothyBrian · 10-25-2011, 01:23 AM

lik in the output.. thanks hen770

Tinkster · 10-25-2011, 01:31 AM

Hi, welcome to LQ!

What's the practial application of this, what languages are you
contemplating to use?

Cheers,
Tink

TimothyBrian · 10-25-2011, 01:53 AM

UNIX scripting.. thanks..

grail · 10-25-2011, 02:15 AM

So a posix shell script (assuming full Unix environment)? What have you tried? Where are you stuck?

David the H. · 10-25-2011, 10:29 AM

It usually helps to explain the context of your problem in detail. Otherwise you force people to waste time asking about why you need it and the environment you're working in, and so on. What exactly are you doing, and why?

I have a possible bash solution ready to go, but I'd like to get some clarification before posting it.

Juako · 10-25-2011, 11:07 AM

The following sed oneliner might help:

Code:

sed 's/\([0-9]\)\([0-9]\)/\2\1/g'

David the H. · 10-27-2011, 01:13 PM

Well, the OP never returned to provide the requested details. Why does that seem to happen so often?

I like Juako's sed command. I should've thought of it. It could be simplified a bit though:

Code:

sed -r 's/(.)(.)/\2\1/g'

This will handle strings of any character (except the delimiter you use), not just numbers.

Anyway, here are the shell versions I came up with. First in bash:

Code:

#!/bin/bash

while read -n 2 line ; do

     printf "%s%s" "${line:1:1}" "${line:0:1}"

done <<<"$1"

echo

exit 0

Now for a posix-compliant shell. It requires a little more work, and an external tool like cut or expr.

Code:

#!/bin/sh

line="$1"

n1=1 n2=2
while [ "$n1" -le "${#line}" ]; do

	printf '%s%s' "$( expr substr "$line" $n2 1 )" "$( expr substr "$line" $n1 1 )"
	n1=$(( n1 + 2 )) n2=$(( n2 + 2 ))

done

echo

exit 0

grail · 10-27-2011, 07:59 PM

Only cause David started it

Code:

#!/bin/bash

line=$1

for (( i = 0; i <= ${#line}; i += 2 ))
do
    ret+=${line:i+1:1}${line:i:1}
done

echo $ret

chrism01 · 10-28-2011, 12:26 AM

@David the H.: sounds like a very arbitrary requirement (ie homework ..) and it's new Academic year time in Northern Hemisphere...
I could be wrong of course

David the H. · 10-28-2011, 01:49 AM

Yeah, that's one reason I held off. But after a couple of days of no-show, and someone else posting a (better) solution first, I figured the damage was done and it wouldn't hurt to go ahead and put it up.

Tinkster · 10-28-2011, 02:01 AM

Quote:

Originally Posted by Juako

The following sed oneliner might help:

Code:

sed 's/\([0-9]\)\([0-9]\)/\2\1/g'

Indeed ... as others pointed out: this smacks of homework, and
handing a solution on a silver platter isn't really what LQ is
about. We're trying to encourage pupils/students to find their
own solution; guidance is OK.

Cheers,
Tink

Juako · 10-28-2011, 08:00 AM

Sorry, I know what Tinkster says is true, and that the OP disappeared but anyway bash is very fun and Grail/David posts have been inspiring

So here is "Bash, functional style"

Code:

#!/bin/bash
(( ${#1} < 3 )) && echo ${1:1:1}${1:0:1} && exit
echo ${1:1:1}${1:0:1}$($0 ${1:2})

Somehow i feel it can be optimized to one line only though ...

grail · 10-28-2011, 11:50 AM

@Juako - good thinking and you were almost there:

Code:

#!/bin/bash

(( ${#1} < 1 )) && exit || echo ${1:1:1}${1:0:1}$($0 ${1:2})