Re: Sed error

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Tue, Aug 2, 2022 at 5:12 PM Aki Hoji <akhst7@xxxxxxxxx> wrote:
>
> I get the error message (sed: -e expression #1, char 2: invalid usage of line address 0) when I run a following;
>
> parallel -a temp3.fq  -k --block 50M --pipe-part 'sed -e  "$!N;/\nXQ@A00165/!P;D"' > temp4.fq

$! is the PID of the last background job.  That's being expanded to 0
because the argument to -e is in double quotes, resulting in an
expression starting with "0N;"

In bash, $! expands to the empty string when there are no background
jobs, rather than to zero.  In that case the expression starts with
"N;" which is also probably not what you meant, but isn't a sed error.

You need to quote the expression so that the $! is not expanded.  This
might work:

EXPR='$!N;/\nXQ@A00165/!P;D' parallel -a temp3.fq  -k --block 50M
--pipe-part 'sed -e  "$EXPR"'