1. CSC 352– Unix Programming, Spring 2016, Final Exam Guide
Noon section has exam on 11 AM May 3
1:30 section has exam on 11 AM May 5
Exam review held on April 26

2. Variables in bash (review)
VARIABLE=STRING, with no spaces around the =, assigns the STRING into VARIABLE.
In order to make it accessible to children processes, you must export the variable from the shell process that defined it. Use unset to remove a variable binding.
C library functions getenv & putenv manipulate these.
-bash-3.00$ v=1
-bash-3.00$ echo $v 1
-bash-3.00$ bash -c 'echo $v'
-bash-3.00$ export v

3. Shell read and built-in variables.
Use read VARIABLENAME to read the terminal into VARIABLENAME.
Use echo STRING or echo –e STRING to echo to stdout; -e interprets escapes such as \n \t.
Special variables:
$? is exitstatus of exit exitstatus; $0 is argv[0] (program name), $1 is argv[1] (first argument), etc.; shift shifts $2 down to $1, etc.;
$# is number of positional arguments; $* or give all command line arguments; set - - STRINGS sets command line arguments to whatever is in STRINGS.

4. Boolean expressions
Any successful (0) exit status is true, non-0 is false.
Shell’s test primitive tests Shell variables and files. Exit status is 0 for success. [ expression ] is shorthand for test expression.
-bash-3.00$ ls *.out
nohup.out
-bash-3.00$ test -f nohup.out ; echo $?
-bash-3.00$ test -f junk.out ; echo $? 1

5. Shell test or [ ] expressions
Here is the subset to know for the exam:
Numerical comparisons:
-eq, -ne, -gt, -ge, -lt, -le
String comparisons:
s1 = s2, s1 != s2.
Use “$v” or “${v}” if v may be empty; otherwise, a binary comparison operator won’t see empty string.
File tests:
-f, -r, -w, -x, -d.
Know how to add to a variable using expr or (( )).
There are no regular expressions in the exam.

6. Boolean connectives && is logical AND, || is logical OR
Both are short-circuited.
&& quits on the first failure, || on the first success.
-bash-3.00$ ls *.out
nohup.out
-bash-3.00$ [ -f nohup.out ] && echo hello
hello
-bash-3.00$ [ -f junk.out ] && echo hello
-bash-3.00$ [ -f nohup.out ] || echo hello
-bash-3.00$ [ -f junk.out ] || echo hello

7. if control construct selects an execution path
Just like you are used to in C++, but
Use elif instead of else if, use fi to end an if construct.
-bash-3.00$ count=`ls *out |wc -l`
-bash-3.00$ echo $count 1
-bash-3.00$ if [ $count -eq 0 ]
> then
> echo none
> elif [ $count -eq 1 ]
> echo one
> else
> echo other
> fi
one

8. while iterates while a text is true
while uses do and done keywords, also break and continue
-bash-3.00$ set -- `date` # set command line arguments
-bash-3.00$ echo "COUNT $# DATA:
COUNT 6 DATA: Sun Mar 27 19:45:36 EDT 2011
-bash-3.00$ i=1
-bash-3.00$ while [ $# -gt 0 ]
> do
> echo "var $i: $1"
> i=`expr $i + 1`
> shift # shift position parameters to the left by one position, discard former $1, decrement $#
> done
var 1: Sun
var 2: Mar
var 3: 27
var 4: 19:49:10
var 5: EDT
var 6: 2011

9. for loops over a list of values
-bash-3.00$ ls -d s* splitstudents startup -bash-3.00$ for f in `ls -d s*` > do > echo "file: $f" > done file: splitstudents file: startup -bash-3.00$ find ~/unix -name "s*" -print /export/home/faculty/parson/unix/seeargs /export/home/faculty/parson/unix/seeargs/seeargs.c /export/home/faculty/parson/unix/seeargs.zip -bash-3.00$ for path in `find ~/unix -name "s*" -print` > echo "file `basename $path` in directory `dirname $path`" file seeargs in directory /export/home/faculty/parson/unix file seeargs.c in directory /export/home/faculty/parson/unix/seeargs file seeargs.zip in directory /export/home/faculty/parson/unix

10. Know how to write a shell function
arg1=$1 # $1 is the first argument to a function when inside that function.
arg2=$2
echo f: $arg1 $arg2 }
set -- Y Z
echo $1 $2
Y Z
f a b
f: a b
f 1 2
f: 1 2
echo $1 $2 # the “global $1 $2” are outside the scope of the function’s $1 $2 etc.

11. Know how to write a Python function with a simple “if” “while” or “for” control construct.
def f(a,b): if a <= b: for i in range(a,b+1): print "Range:", i else: while a >= b: # a > b the first time through print "Downrange:", a a -= 1 # See example run on next slide.

12. Know how to write a Python function with a simple “if” “while” or “for” control construct.
>>> f(0,0) Range: 0 >>> f(0,2) Range: 1 Range: 2 >>> f(2,0) Downrange: 2 Downrange: 1 Downrange: 0