Black on selection

black_selection.sh

#!/usr/bin/env bash

# Source: https://blog.godatadriven.com/black-formatting-selection
# Added debugging prints, permissioning/cleanup, and also a bugfix for
# selecting whole file.

# Print commands/arguments for debugging
set -x

# Inputs
black=$1
input_file=$2
start_line=$3
end_line=$4

# Read selected lines from input file
selection=$(sed -n "$start_line, $end_line p; $((end_line+1)) q" < "$input_file")
tmpfile=$(mktemp)
chmod 600 "$tmpfile"  # Only user can read/write (not execute), for security

# Write to tmpfile and apply Black formatting
echo "$selection" > "$tmpfile"
$black "$tmpfile"

# Print tmpfile for debugging
echo -e "Reformatted code:\n---------------\n$(cat "$tmpfile")\n---------------"

# Delete original lines from input file
sed -i "" "$start_line,$end_line d" "$input_file"

# sed doesn't work on empty file, just assume if start line is 1, that the
# whole file was selected.
if [ "$start_line" == 1 ]
then
  # sponge wasn't originally installed on my Mac... brew install moreutils
  cat "$tmpfile" "$input_file" | sponge "$input_file"  # prepend
else
  sed -i "" "$((start_line-1)) r $tmpfile" "$input_file"
fi

# Cleanup tmpfile
rm -f "$tmpfile"