Why does this sed command do nothing inside a bash script but work outside?

Question

 # join pairs of lines side-by-side (like "paste")
 sed '$!N;s/\n/ /'

The above script comes from the great list of sed one-liners found on sourceforge.

I wish to use it in an a bash script but it has no effect if used inside the script. If I pipe the output of the script through it, it joins join pairs of lines side-by-side as described.

Some character must need escaping but I just can't "see" which character needs to be escaped to make it work inside a bash script.

Yoroshiku Onegaishimasu!

Later..

#!/bin/bash
# numbers.sh

for X in 1 2 3 4 5 6 7 8 9 0
do
        echo $X
done

When used this script:

#!/bin/bash

./numbers.sh | sed '$!N;s/\n/ /'

works fine..

1 2
3 4
5 6
7 8
9 0

Please let me regroup my thoughts on this..

Later...

I found the logical error in the script which broke it.

Answer 1

It's not obvious to me what the problem is without seeing your script. A quick test here and it worked just fine inside of a simple script:

#!/bin/bash
cat /etc/crontab | sed '$!N;s/\n/ /'

If you're trying to embed the command inside a string or variable, the \n will be an escape candidate.

For what it's worth, there's rarely a 'strong' case for making bash-specific scripts over straight up /bin/sh posix-compliant shell scripts unless you really need the advanced containers (which is rare). You'll end up with a script that is considerably more portable to dozens of other posix/korn/bourne-compatible shells (including bash).

Cheers! Sean

Answer 2

Are you missing the "$@" to indicate the file name arguments - so it was only reading from standard input?

What was the misbehaviour? Was the file simply copied to standard output?

Works for me - under Cygwin. 'al' is a program that lists its arguments one per line.

$ al a b c d e f  | sed '$!N;s/\n/ /'
a b
c d
e f
$ cat xxx
sed '$!N;s/\n/ /'
$ al a b c d e f g | bash xxx
a b
c d
e f
g
$