Wrap a command with an SQLite read lock on given files so they can safely be backed up

wrap-sqlite-backup.sh

#!/usr/bin/env bash
# 
# This script wraps a command with a read lock on given SQLite databases
# Example: wrap-sqlite-backup.sh *.sqlite3 -- tar cvzf backup.tgz *.sqlite3
#
# Note that it doesn't check for errors, so it really only works in WAL mode.
# Updates that read from ${COPROC[0]} to check errors welcome.
# 
# [email protected]
# https://gist.github.com/wmertens/4df207197074f9cb93f003c1cb723b4c

# exit on any error
set -e

DBs=
while [ -n "$1" ] && [ "$1" != "--" ]; do
	DBs="$DBs $1"
	shift
done
if [ "$1" != "--" ]; then
	echo "Usage: $0 sqliteDbFiles... -- command args..." >&2
	exit 1
fi      
shift

# We run the sqlite CLI in a coprocess and acquire read locks on all DBs
coproc sqlite3
# We can send command on this fd. We're ignoring the output fd.
I=${COPROC[1]}

function close() {
	echo ".quit" >&$I
	wait
}
# Try to close coproc on script exit
trap close 0

for i in $DBs; do
	n=$(basename "$i")
	echo "ATTACH DATABASE '$i' AS \"$n\"; PRAGMA \"$n\".wal_checkpoint(FULL);" >&$I
done    
echo "BEGIN;" >&$I
for i in $DBs; do
	n=$(basename "$i")
	# This is enough to acquire a read lock
	echo "SELECT 1 FROM \"$n\".sqlite_master;" >&$I
done

# Now wait for the command to complete
# Since this is the last command, it will determine the exit code
"${@}"

# The trap above will close sqlite3