conf-manipulate.sh

#!/usr/bin/env dash

# arguments
section='epel-debuginfo'
key='gpgcheck'
value='0'
state="absent"
file="./epel.repo"
separator="="

# what is the line number of the desired section?
foundsection=""
# are we currently parsing through the desired section?
insection=0
# what is the line number of the found variable?
foundkey=""

contents=`cat -n ./epel.repo`

IFS='
'
for line in $contents; do
  echo $line | egrep -q "\[.*\]"
  if [ "$?" = "0" ]; then
      # this is a section marker
      echo $line | fgrep -q "[$section]"
      if [ "$?" = "0" ]; then
          foundsection=`echo $line | sed -e 's/^ *\([0-9]*\).*$/\1/'`
          insection=1
      else
          insection=0
      fi
  fi

  if [ "$insection" = "1" ]; then
      echo $line | egrep -q "^\s*[0-9]*\s*$key"
      if [ "$?" = "0" ]; then
          foundkey=`echo $line | sed -e 's/^ *\([0-9]*\).*$/\1/'`
      fi
  fi
done

replaceline () {
  file=$1
  from=$2
  to=$3
  newline=$4
  bakfile="$file".bak

  mv $file $bakfile
  head -$from $bakfile > $file
  [ "x$newline" != "x" ] && echo $newline >> $file
  tail -n+`expr $to + 1` $bakfile >> $file
}

if [ $state = "present" ]; then
    newline=$key$separator$value

    # if we want the variable to exist, and it does, we replace it
    if [ "x$foundkey" != "x" ]; then
        replaceline $file `expr $foundkey - 1` $foundkey $newline
    else
        replaceline $file $foundsection $foundsection $newline
    fi
else
    # if we want the variable not to exist, and it does, we delete it
    if [ "x$foundkey" != "x" ]; then
        replaceline $file `expr $foundkey - 1` $foundkey
    fi
fi