test-writable

#!/bin/bash

readonly service_cfg=${0%/scripts*}/etc/service.cfg

. ${service_cfg}
readonly log_file=${service_log}
readonly log_facility="${service}"
. ${scripts_base}/common

check_params "target user" $0 $@

readonly target=$1
readonly user=$2

# http://stackoverflow.com/a/14104522
# http://stackoverflow.com/a/14318764
# Use -L to get information about the target of a symlink,
# not the link itself, as pointed out in the comments
target_info=( $(stat -Lc "0%a %G %U" ${target}) )
perm="${target_info[0]}"
group="${target_info[1]}"
owner="${target_info[2]}"

access=1

readonly aw=$((${perm}&0002))
readonly gw=$((${perm}&0020))
readonly uw=$((${perm}&0200))

if [ ${aw} -ne 0 ]; then
    # Everyone has write access
    access=0
elif [ ${gw} -ne 0 ]; then
    # Some group has write access.
    # Is user in that group?
    gs=( $(groups ${user}) )
    for g in "${gs[@]}"; do
        if [[ ${group} == ${g} ]]; then
            access=0
            break
        fi
    done
elif [ ${uw} -ne 0 ]; then 
    # The owner has write access.
    # Does the user own the file?
    [[ ${user} == ${owner} ]] && access=0
fi

exit ${access}