rename

#!/usr/bin/env bash
#
# rename
#   rename.ul replacement with different/better options
#
# desc
#   debian removed rename.ul from its util-linux installation, so we have to
#   write our own.  while we're at it, we add a couple options to make
#   it easier to to prepend or append something without needing empty string
#   argument (which only works to append), although we still take one to allow
#   the interface to be used the same way
#
# ref
#   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=982944
#
# scott@smemsh.net
# https://github.com/smemsh/utilsh/
# https://spdx.org/licenses/GPL-2.0
#

eval set -- $(getopt -n "${0##*/}" \
-o h1p:a:P:A: \
-l help,firstonly,prepend:,append:,unprepend:,unappend: \
-- "$@")
while true; do case $1 in
(-p|--prepend) prepend="$2"; shift 2;;
(-a|--append) append="$2"; shift 2;;
(-P|--unprepend) unprepend="$2"; shift 2;;
(-A|--unappend) unappend="$2"; shift 2;;
(-1|--firstonly) firstonly=1; shift;;
(-h|--help) cat <<-%
	-p/--prepend <string to add to beginning>
	-a/--append <string to add to end>
	-P/--unprepend <string to remove from beginning>
	-A/--unappend <string to remove from end>
	%
	echo "read script for more usage" >&2; false; exit;;
(--) shift; break;;
(*) echo "impossible condition" >&2; false; exit;;
esac; done

###

for v in append prepend unprepend unappend
do let has_$v=0; done
if [[ $append ]]; then has_append=1; to="$append"
elif [[ $prepend ]]; then has_prepend=1
elif [[ $unprepend ]]; then has_unprepend=1
elif [[ $unappend ]]; then has_unappend=1
else from="$1"; to="$2"; shift 2
fi

optsum=$((has_prepend + has_append + has_unprepend + has_unappend))
if ((optsum && optsum != 1))
then echo "only one operation at a time is supported" >&2; false; exit; fi

for file
do
	if [[ $file == '.' || $file == '..' ]]
	then echo "skipping '$file'" >&2; continue; fi

	if [[ $file =~ '/' ]]
	then echo "skipping path '$file'" >&2; continue; fi

	if ((has_prepend)); then newname="$prepend$file"
	elif ((has_unprepend)); then newname="${file/#$unprepend/}"
	elif ((has_unappend)); then newname="${file/%$unappend/}"
	elif [[ $from == '' ]] || ((has_append)); then newname="$file$to"
	else
		if ((firstonly))
		then newname="${file/$from/$to}"
		else newname="${file//$from/$to}"
		fi
	fi

	if ! mv "$file" "$newname"
	then echo "failed to mv '$file' '$newname'"; false; fi
done