#!/bin/bash

# format-subst <infile> [ <outfile> ]

# Expands git's export-subst formatting placeholders in infile to outfile,

# thus producing the same result as if infile had been git-archived.

# Example:

# $ ./format-subst LICENSE.txt

# The MIT License (MIT)

# Copyright (c) 1985-2019...Applied Logic Systems, Inc.

# ...

set -Eeuo pipefail

INFILE=$1

OUTFILE=${2:-/dev/stdout}

# Only attempt substitution in a git tree, otherwise just cat-copy

if git rev-parse --is-inside-work-tree >/dev/null 2>&1

then

# Extract text from infile, striped of export-subt $Format:...$ syntax

TEXT=$(sed 's/\$Format:\(.*\)\$/\1/g' "$INFILE")

# Use text as git-log formatting template to produce outfile

git log -1 --format="$TEXT" > "$OUTFILE"

else

cat "$INFILE" > "$OUTFILE"

fi