read sftp password from .netrc

netrc-askpass

#!/bin/bash
# Usage: SSH_ASKPASS_REQUIRE=force SSH_ASKPASS=netrc-askpass sftp ...
if [[ $1 =~ ([[:graph:]]+)@([[:graph:]]+)\'s\ password: ]]; then
  USER="${BASH_REMATCH[1]}"
  HOST="${BASH_REMATCH[2]}"
  state=token
  while read -a WORDS; do
    for WORD in ${WORDS[@]}; do
      case $state in
      token)
        case "${WORD}" in
        machine)
          state=machine
          ;;
        login)
          state=login
          ;;
        password)
          state=password
          ;;
        esac
        ;;
      machine)
        machine="${WORD}"
        state=token
        ;;
      login)
        login="${WORD}"
        state=token
        ;;
      password)
        password="${WORD}"
        state=token
        if [[ "$machine" == "$HOST" ]] && [[ "$login" == "$USER" ]]; then
          echo "$password"
          exit 0
        fi
        ;;
      esac
    done
  done < ~/.netrc
fi
exit 1