Shell Foo - Right said sed...

Ugh.. this one was a serious PITA.

For as long as I can recall, I have been using the following command

$ sed -i -e 's/foo/bar/g' file.txt

which would swap every occurrence of the word 'foo' with 'bar'.

Today, I was attempting to swap 'MyCertificateARN' with a variable $CERTIFICATEARN

$ sed -i 's/MyCertificateARN/${CERTIFICATEARN}/g' file.txt
sed: -e expression #1, char 69: unknown option to `s'

Huh? So, I tried substituting in other variables as a test, using actual text, swapping the ' with "... nothing was working correctly.
I then echo'd the variable

$ echo ${CERTIFICATEARN}
arn:aws:acm:us-east-1:427832613400:certificate/57c534b7-4560-4610-a084-ad78d906d8df

Wait.. there's a '/' in there.  After digging for quite a while, I discovered you can use whatever regex delimiter you want for the sed command.

$ sed -i "s|MyCertificateARN|${CERTIFICATEARN}|g" ${OUTPUT}''

$ grep "cate/" $OUTPUT
    "ParameterValue": "arn:aws:acm:us-east-1:427832613400:certificate/57c534b7-4560-4610-a084-ad78d906d8df"

case `sed --version | head -1` in
  *GNU*)
    # Add the '[' to the beginning of the file
    sed -i -e '1i[' ${OUTPUT}
    # Remove the trailing ',' from the last entry
    sed  -i '$ s/},/}/' ${OUTPUT}
    # Insert the correct Certificate ARN (use alt regex delimiter for this as ARN contains a /)
    sed -i "s|MyCertificateARN|${CERTIFICATEARN}|g" ${OUTPUT}
  ;;
  *)
sed -i'' '1i\
[\
' ${OUTPUT}
  ;;
esac
echo "]" >> ${OUTPUT}