The driving idea of UNIX
portable
Unix written in C, with some assembly code.
Not welded to the computer used
multi-tasking, multi-user
simple and light-weight
use of”flat” plain text files – user-readable code
large number of software tools
hierarchical file system
Sending messages to other processes: echo “
File/device notification:
files: can read and write chars or blocks of data
devices:
char devices (eg keyboard) – read chars, not seekable
/dev/pts10
block devices (eg HDD) – read blocks of data, seekable
pseudo devices:
/dev/zero: produces zeros
/dev/null: ignores all input, has no output
/dev/random: produces a stream of rand output
Unix shell
allows “shell scripting”
can write “for loop” to create 10 .txt files.
for i in 0 1 2 3 4 5 6 7 8 9
do
touch $i.txt
can tie processes together
Selective rules for programming:
rule of modularity:
write simple modules connected via clean interface
rule of clarity:
clarity >> cleverness
rule of composition:
design programs to be connected with other programs
rule of user input:
do not make programs WAIT for user input
rule of simplicity:
add complexity only if you must
rule of transparency:
make inspection and debugging easy – a good man page helps.
rule of robustness:
program should work well, but if it fails, make sure it fails gracefully.
Do input checking
rule of least surprise:
in interface design, always do the least surprising thing
stick with convention (+ means add)
avoid excessive features and novelty (max of 3 clicks to go to ANY file on iPod)
rule of silence:
when program has nothing surprising to say, it should say nothing.
rule of repair:
when you must fail, fail noisily and as soon as possible
rule of (late) optimisation:
get it working before optimising it.
