Awk adding a pipe at the end of the first line - awk

Question

I have a little problem with my awk command.
The objective is to add a new column to my CSV :
The header must be "customer_id"
The next rows must be a customer_id from an array
Here is my csv :
email|event_date|id|type|cha|external_id|name|date
abcd#google.fr|2020-11-13 08:04:44|12|Invalid|Mail|disable|One|2020-11-13
dcab#google.fr|2020-11-13 08:04:44|13|Invalid|Mail|disable|Two|2020-11-13
I would like to have this output :
email|event_date|id|type|cha|external_id|name|date|customer_id
abcd#google.fr|2020-11-13 08:04:44|12|Invalid|Mail|disable|One|2020-11-13|20200
dcab#google.fr|2020-11-13 08:04:44|13|Invalid|Mail|disable|Two|2020-11-13|20201
But when I'm doing the awk I have this result :
awk -v a="$(echo "${customerIdList[#]}")" 'BEGIN{FS=OFS="|"} FNR==1{$(NF+1)="customer_id"} FNR>1{split(a,b," ")} {print $0,b[NR-1]}' test.csv
email|event_date|id|type|cha|external_id|name|date|customer_id|
abcd#google.fr|2020-11-13 08:04:44|12|Invalid|Mail|disable|One|2020-11-13|20200
dcab#google.fr|2020-11-13 08:04:44|13|Invalid|Mail|disable|Two|2020-11-13|20201
Where customerIdList = (20200 20201)
There is a pipe just after the "customer_id" header and I don't know why :(
Can someone help me ?

Answer 1

Could you please try following, written and tested with shown samples.
awk -v var="${customerIdList[*]}" '
BEGIN{
num=split(var,arr," ")
}
FNR==1{
print $0"|customer_id"
next
}
{
$0=$0 (arr[FNR-1]?"|" arr[FNR-1]:"")
}
1
' Input_file
Explanation: Adding detailed explanation for above.
awk -v var="${customerIdList[*]}" ' ##Starting awk program from here, creating var variable and passing array values to it.
BEGIN{ ##Starting BEGIN section of this program from here.
num=split(var,arr," ") ##Splitting var into arr with space delimiter.
}
FNR==1{ ##Checking condition if this is first line.
print $0"|customer_id" ##Then printing current line with string here.
next ##next will skip all further statements from here.
}
{
$0=$0 (arr[FNR-1]?"|" arr[FNR-1]:"") ##Checking condition if value of arr with current line number -1 is NOT NULL then add its value to current line with pipe else do nothing.
}
1 ##1 will print current line.
' Input_file ##Mentioning Input_file name here.

Answer 2

awk -v IdList="${customerIdList[*]}" 'BEGIN { split(IdList,ListId," ") } NR > 1 { $0=$0"|"ListId[NR-1]}1' file
An array will need to be created within awk and so pass the array as a space separated string and then use awk's split function to create the array IdList. The ignoring the headers (NR>1), set the line equal to the line plus the index of ListId array NR-1.