lcfold2-2

#! /bin/sh

# lcfold2-2 - fold long lines using <backslash><newline><backslash>
#             for line continuation
# Copyright (C) 2019,2022  Erik Auerswald <auerswal@unix-ag.uni-kl.de>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# Fold (line wrap) long lines as described in Internet Draft (I-D)
# draft-ietf-netmod-artwork-folding-04, now RFC 8792. In this script
# Strategy 2 ('\\') of line wrapping described in the I-D is used. The
# I-D requires a header to signal beginning of text with folded (wrapped)
# lines, but no footer to signal the end of folded text. This script
# adds the header. The maximum line length is hard-coded to 69.

printf -- "NOTE: '%s' line wrapping per RFC 8792\n\n" '\\'
sed -E '{H;$!d};x;s/^\n//;s/(\\)(\n *\\)/\1\\\n\\\2/g' -- "$@" | \
sed -E 's/(.{68})(..)/\1\\\n\\\2/;tMORE;bEND;:MORE;P;D;:END'