BASH - echo issues, wont print anything but while read argument - bash

Question

We are having a wierd issue.
We have this lines :
while read line2; do
echo $line2
done < $1 | `echo grep '.*|.*|.*|.*|.*|.*|.*|.*'` | sort -nbsk1 | cut -d "|" -f1 | uniq -d
Which prints what they should print. but, when changing the echo to ->
while read line2; do
echo "Hello World"
done < $1 | `echo grep '.*|.*|.*|.*|.*|.*|.*|.*'` | sort -nbsk1 | cut -d "|" -f1 | uniq -d
It wont print anything, same result for anything different then $line2.
Whats even more wierd is :
echo " $line2 Hello"
Will print the line2 variable
echo "Hello $line2"
Print nothing
I have tried the same with printf, same results.
Any suggestions ?

Answer 1

What you've written is equivalent to the following shell code:
cat $1 |
while read line2; do
echo $line2
done |
`echo grep '.*|.*|.*|.*|.*|.*|.*|.*'` |
sort -nbsk1 |
cut -d "|" -f1 |
uniq -d
The while read loop takes the contents of file $1 and echoes them, which does nothing other than remove leading and trailing spaces and replace internal spaces with a single space. If you replace the echo $line2 line with echo "Hello World", that string is clearly not going to match the grep command that the output of the loop is being passed through, so producing no output is unsurprising.
When you change the echo line to echo " $line2 Hello", you tack "Hello" onto the end of the input line, which then matches the grep command and gets sliced off the end of the string with the cut command, so it makes sense that it would have essentially no ultimate effect.
If you change the echo line to echo "Hello $line2", any number at the beginning of the line becomes invisible to the sort -ns, which makes your sort call essentially a no-op. This is probably why you're not seeing anything in this situation, although you probably would see something if two identical lines appeared in the input one after the other. (In my testing on my machine, I see one such line because I happen to have two identical lines in succession in my test case.)
It's not exactly clear what you're trying to do since the while loop is almost a no-op. It's possible what you want to do is something more like this:
grep '.*|.*|.*|.*|.*|.*|.*|.*' < $1 |
sort -nbsk1 |
cut -d "|" -f1 |
uniq -d |
while read line2; do
echo $line2
done
... but I'm only speculating at this point.