# In previous, we have learned how permission bits are represented
# in 2 related but slightly different ‘human readable’ formats. At
# the machine level, though, those bits are simply a 9-bit number
# (or rather, 9 bits out of a 16 bit number). Since the 9 bits are
# grouped into 3 groups of 3 bits each, it is convenient to
# represent them in octal, where each digit corresponds to 3 bits.

# Let's first look at the bits that represent various human-readable
# triplets:
#
#  • ‹rwx› → ‹111›
#  • ‹rw-› → ‹110›
#  • ‹r-x› → ‹101›
#  • ‹-wx› → ‹011›
#
# ... and so on ...
#
# The octal digits correspond to 3-bit binary numbers as follows:
#
#  • ‹0› → ‹000›
#  • ‹1› → ‹001›
#  • ‹2› → ‹010›
#  • ‹3› → ‹011›
#  • ‹4› → ‹100›
#  • ‹5› → ‹101›
#  • ‹6› → ‹110›
#  • ‹7› → ‹111›
#
# The digits are written in the same order as with the human
# readable form: owner, group and others, from the left. Hence:

touch file.txt

printf "755: "
chmod 755 file.txt
ls -l file.txt

printf "750: "
chmod 750 file.txt
ls -l file.txt

printf "644: "
chmod 644 file.txt
ls -l file.txt

# Let's have a quick look at how directory permissions work now:
# ‹dir.sh›.