Você pode fazer assim:
#!/bin/bash
URLTOSEARCH="$1"
FILENAME="npmrc"
# you have to give an url
# so the search can begin
if [ -z "$URLTOSEARCH" ]; then
echo "Please enter an url to search."
exit 1
fi
# first, get the link
# out of the file
while read -r line
do
# get the url
EXTRACTEDURL=$(echo "$line" | grep -o '//.*/:' | sed 's/\/:/\//g')
# get the token
EXTRACTEDTOKEN=$(echo "$line" | grep -o '_authToken=.*' | sed 's/_authToken=//g')
if [ "//$URLTOSEARCH/" == "$EXTRACTEDURL" ]; then
echo "Token found: $EXTRACTEDTOKEN"
fi
done < "$FILENAME"