#!/bin/sh
# Filter lines of input with a shell predicate.
#   Usage: filter [varname (default: x)] predicate
#   Example: ls | filter '[ -d "$x" ] && expr "$x" : ".*[0-9]"'
[ $# -gt 1 ] && var="$1" && shift || var=x
sh -c "while IFS= read -r $var; do
    $@ >/dev/null && echo \"\$$var\"
done" || true