1. CSC 352– Unix Programming, Spring 2016
April 2016
A few final commands

2. Based on 2015 assn 3 solutions
These are some bash shell mechanisms and Unix utilities used by students in assignment 3 that can be very useful.
I had forgotten about some of these.
Some may be buried in or missing from the textbook.
I always learn or re-learn when teaching Unix.

3. bc – the “bench calculator”
It reads standard input, not command line.
Following POSIX bc operators behave exactly like their C counterparts:
+ - * /
+= -= *= /=
++ -- < >
== != <= >=
( ) [ ] { }
GNU bc has others, but they are not portable.

4. Some bc examples [:-) ~] echo '1.1 + 20 * -2.0' | bc -38.9
[:-) ~] bc << EOF
* -2.0
EOF
Latter is a “here document” for supplying literal text to standard input.
Note that 0 means false and non-0 means true in a bc expression, just like C & C++, but opposite of shell exit status.

5. Some pitfalls in = assignment
[:-) ~] expression=' * -2.0'
[:-) ~] echo $expression
bignum.py ... FILES
Glob matching captures the *
[:-) ~] expression=' \* -2.0'
\* -2.
The backslash is now part of the string.

6. More pitfalls in = assignment
expression=" * -2.0” glob matches
expression=" \* -2.0” captures \
[:-) ~] expression= \* -2.0
-bash: +: command not found
[:-) ~] set –f # SHUT OFF GLOBBING
[:-) ~] ls *
ls: cannot access *: No such file or directory
[:-) ~] expression=' * -2.0'
[:-) ~] echo $expression
* -2.0
[:-) ~] echo $expression | bc
-38.9

7. “No spaces” works without -f
[:-) ~] expression='1.1+20*-2.0'
[:-) ~] echo $expression
1.1+20*-2.0
[:-) ~] echo $expression | bc
-38.9

8. [[ EXPRESSION ]] [[ expression ]]
Return a status of 0 or 1 depending on the evaluation of the conditional expression expression. Expressions are composed of the primaries described below under CONDITIONAL EXPRESSIONS. Word splitting and pathname expansion are not performed on the words between the [[ and ]]; tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process substitution, and quote removal are performed. Conditional operators such as -f must be unquoted to be recognized as primaries.

9. [[ … ]] examples
[:-) ~] [[ a -lt 4 && a -gt 2 ]]
[:-) ~] echo $?
You can use logical connectives && and || inside the test brackets.

10. [[ … ]] regular expression matching
[:-) ~] number='^(([0-9]+(\.[0-9]*)?)|([0-9]*\.[0-9]+))$’
The \. Is necessary to match literal “.” -- . by itself matches any char.
[:-) ~] [[ 1 =~ $number ]] ; echo $?
[:-) ~] [[ 1. =~ $number ]] ; echo $?
[:-) ~] [[ 1.1 =~ $number ]] ; echo $?
[:-) ~] [[ .1 =~ $number ]] ; echo $?
[:-) ~] [[ 1f =~ $number ]] ; echo $? 1

11. egrep (extended grep) patterns
pattern * 0 or more occurrences of previous character or (expression) pattern + 1 or more occurrences of previous character or (expression) pattern ? 0 or 1 occurrence of previous character or (expression) pattern . any single character pattern [pqr] any single character from set p, q or r pattern [a-zA-Z] any single character from range a-z or A-Z pattern [^pqr] any single character *not* from set p, q or r pattern ( EXPR ) is for subexpression grouping pattern P1 | P2 is for pattern P1 or P2 pattern ^ the start of the string being searched for a match pattern $ the end of the string being searched for a match pattern \ escapes the next character so it is treated as a regular char These are the most useful regular expression patterns available to grep, sed, [[ $string =~ $pattern ]] tests, and for searching in emacs and vi. The shell uses so-called “glob-style matching” for strings (*.java), which differ from regular expressions (.*\.java) used by grep, sed, emacs and vi.

12. Regular expression examples p.1
[:-) ~/unix] cat re1.txt
abcdefg
123abc
ABCDEFGHIJKLM
AaAaBbVv
[:-) ~/unix] egrep '[0-9]+' re1.txt

13. Regular expression examples p.2
[:-) ~/unix] egrep '^[0-9]+$' re1.txt
[:-) ~/unix] egrep '^[0-9]*$' re1.txt
[:-) ~/unix] egrep '[0-9]*' re1.txt
abcdefg
123abc
ABCDEFGHIJKLM
AaAaBbVv

14. Regular expression examples p.3
[:-) ~/unix] egrep '[0-9]+.?[0-9]*' re1.txt
123abc
[:-) ~/unix] egrep '^[0-9]+.?[0-9]*$' re1.txt
[:-) ~/unix] egrep '^[0-9]+[^0-9][0-9]*$' re1.txt
[:-) ~/unix] egrep '^[0-9]+[^0-9]?[0-9]*$' re1.txt
[:-) ~/unix] egrep '^[0-9]+[^0-9]?[A-Fabcdef]+$' re1.txt

15. Regular expression examples p.4
[:-) ~/unix] egrep '(([0-9]+)|([A-Za-z]+))$' re1.txt
abcdefg
123abc
ABCDEFGHIJKLM
AaAaBbVv
[:-) ~/unix] egrep '[^A-Za-z0-9]+$' re1.txt

16. Regular expression examples p.5
[:-) ~/unix] egrep '[^A-Za-z0-9]?$' re1.txt
abcdefg
123abc
ABCDEFGHIJKLM
AaAaBbVv
[:-) ~/unix] egrep '[^A-Za-z0-9]*$' re1.txt

17. sed writes to standard output, sed –r uses extended Res p.1
[:-) ~/unix] egrep '[^A-Za-z0-9]+$' re1.txt
[:-) ~/unix] sed -e 's/[^A-Za-z0-9]+$/AllFixedUp/g' re1.txt
abcdefg
123abc
ABCDEFGHIJKLM
AaAaBbVv

18. sed writes to standard output, sed –r uses extended Res p.1
[:-) ~/unix] sed -r -e 's/[^A-Za-z0-9]+$/AllFixedUp/g' re1.txt
abcdefg
123abc
AllFixedUp
ABCDEFGHIJKLM
AaAaBbVv
sed does NOT modify the source file. It sends to stdout but you could:
sed -r -e 's/[^A-Za-z0-9]+$/AllFixedUp/g' re1.txt > tmpfile.txt
mv tmpfile.txt re1.txt

19. [[ =~ ]] pattern matching
[:-) ~/unix] pattern='^[0-9]+.?[a-z]*$'
[:-) ~/unix] echo $pattern
^[0-9]+.?[a-z]*$
[:-) ~/unix] for line in `cat re1.txt`
> do
> if [[ $line =~ $pattern ]] # [[ ! $line =~ $pattern ]] for non-matching lines
> then
> echo "MATCH $line"
> fi
> done
MATCH
MATCH 123abc