#!/bin/sh

# POSIX compliant regular expressions
# Matches any string that contains a null byte or begins or ends with a /
REGEX1='(^/|/$|\\0)'
# Matches any string longer than 255 characters (for a single filename)
REGEX2='^.{256,}$'
# Matches any string longer than 4096 characters (for a full path)
REGEX3='^.{4097,}$'

if echo "$1" | grep -Eq "$REGEX1" || echo "$1" | grep -Eq "$REGEX2" || echo "$1" | grep -Eq "$REGEX3"; then
    # If any regex matches, this is an invalid path
    exit 1
else
    # Otherwise, it's valid
    exit 0
fi