In regex101: https://regex101.com/r/FM88LA/1
In my browser console:
x='"AbCd123|999"';
"\"AbCd123|999\""
x.match(/[^\""|]+/)
Array [ "AbCd123" ]
Using sed in the shell:
(base) balter@winmac:~/winhome/CancerGraph/TCGA$ echo '"AbCd123|99999"' | sed -En 's/([^\"|]+)/\1/p'
"AbCd123|99999"
(base) balter@winmac:~/winhome/CancerGraph/TCGA$ echo '"AbCd123|99999"' | sed -En 's/\"([^|]+)/\1/p'
AbCd123|99999"
That is all fine, because sed command used with -n option and p flag only prints the text that was not matched + the result of the successful replacement.
That means, you can get your "match" with
echo '"AbCd123|99999"' | sed -En 's/["|]*([^"|]+).*/\1/p'
See the online demo.
Here, the pattern gets to the first char that is not " and | with ["|]*, then the ([^"|]+) part captures one or more chars other than " and |, and then .* matches the rest of the string.
Everything that was matched but not captured is removed as you only ask to print the \1, the Group 1 value (captured with ([^"|]+)).