How to use dynamic field value for gsub? - shell

Question

I have a use case where I need to replace the values of certain fields with some string. The field value has to be picked up from config file at runtime and should replace each character in that field with 'X'.
Input:
Hello~|*World Good~|*Bye
Output:
Hello~|*XXXXX Good~|*XXX
To do this I am using below command
awk -F "~\|\*" -v OFS="~|*" '{gsub(/[a-zA-Z0-9]/,"X",$ordinal_position)}1' $temp_directory/$file_basename
Here I would like to use ordinal_position variable where I will pass the field number.
I have already tried below command but it is not working.
awk -F '~\|\*' -v var="$"25 -v OFS='~|*' '{gsub(/[a-zA-Z0-9]/,"X",var)}1' $temp_directory/$file_basename

Answer 1

Pass the field number as an integer and precede the variable name with a $ (or enclose in $() for better readability) in the awk program for referencing that field. Like:
awk -v var=25 '{ gsub(/regex/, "replacement", $var) } 1' file

Answer 2

Could you please try following, here in awk variable named fields you can mention all the fields which you want to change and rest will be taken care in the solution(like OP has shown 2nd and 3rd fields in samples so putting 2,3 in here OP could change values as per need). Written and tested with shown samples in GNU awk.
awk -v fields="2,3" '
BEGIN{
FS=OFS="|"
num=split(fields,fieldIn,",")
for(i=1;i<=num;i++){
arrayfieldsIn[fieldIn[i]]
}
}
function fieldChange(field_number){
delete array
num=split($field_number,array," ")
gsub(/[a-zA-Z0-9]/,"X",array[1])
for(i=2;i<=num;i++){
val=val array[i]
}
$field_number=array[1] " " val
val=""
}
{
for(j=1;j<=NF;j++){
if(j in arrayfieldsIn){
fieldChange(j)
}
}
}
1
' Input_file
Explanation: Adding detailed explanation for above.
awk -v fields="2,3" ' ##Starting awk program from here and setting value of variable fields with value of 2,3.
BEGIN{ ##Starting BEGIN section of this program here.
FS=OFS="|" ##Setting FS and OFS values as | here.
num=split(fields,fieldIn,",") ##Splitting fields variable into array fieldIn and delimited with comma here.
for(i=1;i<=num;i++){ ##Starting for loop from 1 to till value of num here.
arrayfieldsIn[fieldIn[i]] ##Creating array arrayfieldsIn with index fieldIn here.
}
}
function fieldChange(field_number){ ##Creating function here for changing field values.
delete array ##Deleting array here.
num=split($field_number,array," ") ##Splitting field_number into array with delimiter as space here.
gsub(/[a-zA-Z0-9]/,"X",array[1]) ##Globally substituting alphabets and digits with X in array[1] here.
for(i=2;i<=num;i++){ ##Running for loop from 2 to till num here.
val=val array[i] ##Creating variable val which has array value here.
}
$field_number=array[1] " " val ##Setting field_number to array value and val here.
val="" ##Nullify val here.
}
{
for(j=1;j<=NF;j++){ ##Running loop till value of NF here.
if(j in arrayfieldsIn){ ##Checking if j is present in array then do following.
fieldChange(j) ##Calling fieldChange with variable j here.
}
}
}
1 ##1 will print line here.
' Input_file ##Mentioning Input_file name here.