追記1 busyboxでは以下のコマンドが使用可能です。 [, [[, ar, arch, ash, awk, base64, basename, bash, bunzip2, busybox, bzcat, bzip2, cal, cat, chmod, cksum, clear, cmp, comm, cp, cpio, cut, date, dc, dd, df, diff, dirname, dos2unix, dpkg-deb, du, echo, ed, egrep, env, expand, expr, factor, false, fgrep, find, fold, fsync, ftpget, ftpput, getopt, grep, groups, gunzip, gzip, hd, head, hexdump, id, ipcalc, kill, killall,
