bash - Substitute all characters between two strings by char 'X' using sed

Question

In a Bash script, I am trying to in-file replace the characters between two given strings by 'X'. I have bunch of string pair, between which I want the replacement of characters by 'X' should happen.
In the below code, the first string in the pair is declared in cpi_list array. The second string in the pair is always either %26 or & or ENDOFLINE

This is what I am doing.

# list of "first" or "start" string
declare -a cpi_list=('%26Name%3d' '%26Pwd%3d')  

# This is the "end" string
myAnd=\%26
newfile="inputlog.txt"

for item in "${cpi_list[@]}";
do
    sed -i -e :a -e "s/($item[X]*)[^X](.*"$myAnd")/1X2/;ta" $newfile;
done

The input

CPI.%26Name%3dJASON%26Pwd%3dBOTTLE%26Name%3dCOTT
CPI.%26Name%3dVoorhees&machete

I want to make it

CPI.%26Name%3dXXXXX%26Pwd%3dXXXXXX%26Name%3dXXXX
CPI.%26Name%3dXXXXXXXX&machete

PS: The last item need also change %26Name%3dCOTT to %26Name%3dXXXX even though there is no end %26 because I am looking for either %26 as the end point or the END OF THE LINE

But somehow it is not working.

Answer 1

This will work in any awk called from any shell in any UNIX installation:

$ cat tst.awk
BEGIN {
    begs = "%26Name%3d|%26Pwd%3d"
    ends = "%26|&"
}
{
    head = ""
    tail = $0
    while( match(tail, begs) ) {
        tgtStart = RSTART + RLENGTH
        tgt = substr(tail,tgtStart)
        if ( match(tgt, ends) ) {
            tgt = substr(tgt,1,RSTART-1)
        }

        gsub(/./,"X",tgt)
        head = head substr(tail,1,tgtStart-1) tgt
        tail = substr(tail,tgtStart+length(tgt))
    }
    $0 = head tail

    print
}

$ cat file
CPI.%26Name%3dJASON%26Pwd%3dBOTTLE%26Name%3dCOTT
CPI.%26Name%3dVoorhees&machete

$ awk -f tst.awk file
CPI.%26Name%3dXXXXX%26Pwd%3dXXXXXX%26Name%3dXXXX
CPI.%26Name%3dXXXXXXXX&machete

Just like with a sed subsitution, any regexp metacharacter in the beg and end strings would need to be escaped or we'd have to use a loop with index()s instead of match() so we'd do string matching instead of regexp matching.