Homework & Coursework Questions

#!/bin/sh

# rafactor.sh

if (($# == 0));
    then
    echo "Not enough arguments"

exit 0

fi

if (( -z "$3" ));

BAKDIR="./bakup"
TEMPDIR="./temp"

cd $3

sed 's/$1/$2/g'

if (( -z "$3" ));

if STATEMENT
then
        ...
else
        ...
fi

# Run an external program and execute the code inside if it succeeds.
# externals are things like cut, grep, sed, awk, javac, wget, true, false, ...
if program param1 param2 ...
then
        ...
fi

# Run an external program and execute the code inside if it fails.
# in fact, you can put an ! in front of any STATEMENT.
if ! program param1 param2 ...
then
        ...
fi

# Check a logical statement as described by man test.
# -z for instance means 'test if string is empty'.  There's also operators
# available to compare decimal numbers [ 9 -gt 2 ], [ 3 -lt 5 ], [ 9 -eq 9 ]
# compare strings [ "abc" = "abc" ], [ "def" \> "abc" ], [ "abc" \< "def" ] 
# check for the presence of files [ -e "filename.sh" ]
# check for the presence of directories [ -d "dirname" ], and others.
if [ -z "$3" ]
then
        ...
fi

# [[ ]] are extended versions of [ ].  They support a more "C-like" syntax
# with && instead of -a and such, and are faster than [] in some shells,
# but behave much like [ ] otherwise.
if [[ "aaaa" == "bbbbb" ]]
then
        ...
fi

# This only works in BASH and newer KSH
A=3
B=5
if ((B>A))
then
        ...
fi

package uwindsor.cs256;
public class aaa {
aaa aaaInstance ; // an instance of aaa
int aaaNum=0 ;
public aaa() {
}
}

package uwindsor.cs256;
public class AAA {
AAA aaaInstance ; // an instance of AAA
int aaaNum=0 ;
public AAA() {
}
}

$ echo "slartibartfast q;  int aslartibartfast;  slartibartfast b, c;  int d;" | sed 's/\([ ;]\|^\)slartibartfast\([ ;]\|$\)/\1qwerty\2/g'
qwerty q;  int aslartibartfast;  qwerty b, c;  int d;
$

# Just prints one big long string, and pipes it into sed.
echo "slartibartfast q;  int aslartibartfast;  slartibartfast b, c;  int d;" |
        # sed 's/a/b/g' searches for all a, replaces with b.
        # a can be an entire expression, not just a literal string.
        # Just 's/slartibartfast/qwerty/g' would change our
        # 'aslartibartfast' to 'aqwerty', which is wrong, so we need to check
        # where it is too.
        #
        # [ ;] matches either a semicolon or a space, so
        # [ ;]slartibartfast[ ;] would catch it in the middle of a line, but
        # not the beginning or end.
        #
        # ^ means beginning, $ means end, | means 'or', () group things.  So
        " ([ ;]|^) would mean the beginning of the line or space or semicolon.
        # ([ ;]|^)slartibartfast([ ;]|$) should catch it anywhere in the line.
        #
        # Except if we search-replace that, we're stripping out lots of
        # whitespace and semicolons -- you need those.  You can put back
        # anything you find in () with \1, \2, ... for match 1, match 2 ...
        #
        # So:
        #
        # s/([ ;]|^)slartibartfast([ ;]|)/\1qwerty\2/g'
        # ...tells it to replace ;slartibartfast; with qwerty and put the ;'s back.
        #
        # Except, sed is horrible and won't understand ( | ) unless
        # you put \ in front of them, which makes otherwise-simple expressions
        # capable of blinding small dogs and the elderly.
        #
        #If you have sed -r, you can leave them as-is.
        sed 's/\([ ;]\|^\)slartibartfast\([ ;]\|$\)/\1qwerty\2/g'
# And this is what it prints.  See how it left aslartibartfast alone.
qwerty q;  int aslartibartfast;  qwerty b, c;  int d;
$