Modifying Script Bash Variable From Outside For Searching Patterns

I just want to know if it is possible to read a variable for searching patterns in a existing running bash script which accepts parameters from outside, for example in command-line. Here the example,

# /home/testexp.sh
#!/usr/bin/env bash
PATH=$(/usr/bin/getconf PATH || /bin/kill $$)

echo "$1" # The first parameter that has been set.

readfromfile=$(cat filename1)
if test "$1" = "$readfromfile" ;
then
   echo "excellent"
else
   echo "no no.."
fi

How can i use parameter variable expansion for searching patterns in $readfromfile variable ?

I want to do like:

./testexp.sh ${readfromfile:2:3}

Where i must say, it works only when $readfromfile is set and exported and it has been printed in script. Like:

echo "$1"

But i do not want to modify $1 parameter, i want to search for patterns in $readfromfile variable and bruteforce it when it is equal to $1 parameter.