Bash pattern matching newline character in shell parameter expansion-CodePudding

I have a long variable in my bash script. I'm trying to iterate over it in chunks to do some processing. It's largely working:

    while [ ${#REMAINING_PLAN} -gt 0 ] ; do
      CURRENT_PLAN=${REMAINING_PLAN::65300} # Truncate to 65k and iterate

      # problematic line:
      CURRENT_PLAN=${CURRENT_PLAN%'\\n'*} # trim truncated string to the last newline
      
      PROCESSED_PLAN_LENGTH=$((PROCESSED_PLAN_LENGTH ${#CURRENT_PLAN})) # evaluate length of outbound batch and store
      
      # do some stuff not shown

      REMAINING_PLAN=${REMAINING_PLAN:PROCESSED_PLAN_LENGTH}
    done

I'm trying to truncate a variable to a max length, then further strip everything up to the last new line in the file, so that my next 'batch' starts its processing on a fresh line. But this statement isn't doing what I intend:

CURRENT_PLAN=${CURRENT_PLAN%'\\n'*} # does not actually trim truncated string to the last newline

What's wrong with it and how can I trim a string to the last instance of a newline?

CodePudding user response：

Converting my comment to answer so that solution is easy to find for future visitors.

You may use this in bash to strip off all characters after last line break:

CURRENT_PLAN="${CURRENT_PLAN%$'\n'*}"

$'\n' is C like construct that is used in bash to denote a line break.