scan

#!/bin/bash
#
# Take a pathname as an argument and output a playlist to standard
# output and errors to standard error.
#
# The output format is repeated sequences of:
#
#   <pathname>\t<artist>\t<title>[\t<bpm>]\n
#
# If the tab (\t) or newline (\n) characters appear in a filename,
# unexpected things will happen.

set -eu -o pipefail  # pipefail requires bash, not sh

PATHNAME="$1"

if [ -d "$PATHNAME" ]; then
	find -L "$PATHNAME" -type f -regextype posix-egrep \
		-iregex '.*\.(ogg|oga|aac|cdaudio|mp3|flac|wav|aif|aiff|m4a|wma)'
else
	cat "$PATHNAME"
fi |

# Parse artist and title information from matching filenames

sed -n '
{
# /[<ABnum>[.]] <artist> - <title>.ext
s:/\([A-H]\?[A0-9]\?[0-9].\? \+\)\?\([^/]*\) \+- \+\([^/]*\)\.[A-Z0-9]*$:\0\t\2\t\3:pi
t

# /<artist> - <album>[/(Disc|Side) <name>]/[<ABnum>[.]] <title>.ext
s:/\([^/]*\) \+- \+\([^/]*\)\(/\(disc\|side\) [0-9A-Z][^/]*\)\?/\([A-H]\?[A0-9]\?[0-9].\? \+\)\?\([^/]*\)\.[A-Z0-9]*$:\0\t\1\t\6:pi
t

# /[<ABnum>[.]] <name>.ext
s:/\([A-H]\?[A0-9]\?[0-9].\? \+\)\?\([^/]*\)\.[A-Z0-9]*$:\0\t\t\2:pi
}' |

# Extract BPM metadata from title (eg. "Ghostbusters (115.6 BPM)")

sed '
{
# BPM
s:\(.*\) *(\([0-9]\+\.\?[0-9]\+\) *BPM)$:\1\t\2:
}'