You would need to do something like this to shift the fields:

Code:

awk '{for(i=1; i<=NF; i++) if($i=="") for(j=i;j<=NF;j++)$j=$(j+1)}1' FS=\| OFS=\| infile

output:

Code:

1|2|3|4|5|6||

But that still leaves two empty fields at the back..
So you would need to do something like this to remove those empty fields at the back.

Code:

awk '{for(i=1; i<=NF; i++) if($i=="") for(j=i;j<=NF;j++)$j=$(j+1);NF-=2}1' FS=\| OFS=\| infile

output:

Code:

1|2|3|4|5|6

If you don't know how many field need to be shifted, you would need to calculate the number of empty fields...

But a more straightforward approach would be to just delete field separators:

Code:

awk '{gsub(/^\||\|$/,x);gsub(/\|\|/,"|")}1' infile

output:

Code:

1|2|3|4|5|6

Or if you do not need to use awk:

Code:

sed 's/^|//;s/|$//;s/||/|/g' infile