basicsys@mars~/lec7>echo -e "acdat\nacatb" | egrep "cat|dog"
acatb

basicsys@mars~/lec7>echo -e "adogb\nacat\nacow\ncatb"|egrep "^cat|dog|cow$"
adogb
acow
catb

basicsys@mars~/lec7>cat F1
     ab   cd  shalom
     ab   cd  shalom1
     ab   cd  shalom 123

basicsys@mars~/lec7>cat F1 | egrep "^[ ]*[^ ]+[ ]+[^ ]+[ ]+shalom([ ]|$)"
     ab   cd  shalom
     ab   cd  shalom 123

basicsys@mars~/lec7>echo "ab cd" | egrep "\<ab\>"
ab cd

basicsys@mars~/lec7>echo "ddab cd" | egrep "\<ab\>"

basicsys@mars~/lec7>echo "dd   ab cd" | egrep "\<ab\>"
dd   ab cd

basicsys@mars~/lec7>echo "dd   ab cdab" | egrep "\<ab\>"
dd   ab cdab

basicsys@mars~/lec7>echo "dd   cdab" | egrep "\<ab\>"

basicsys@mars~/lec7>echo "dd   cd ab" | egrep "\<ab\>"
dd   cd ab

basicsys@mars~/lec7>cat F1
     ab   cd  shalom
     ab   cd  shalom1
     ab   cd  shalom 123

basicsys@mars~/lec7>cat F1 | egrep "\<.*\>.*\<.*\>.*\<shalom\>"
     ab   cd  shalom
     ab   cd  shalom 123

basicsys@mars~/lec7>cat F1
     ab   cd  shalom
     ab   cd  shalom1
     ab   cd  shalom 123
xy    ab   cd  shalom 123

basicsys@mars~/lec7>cat F1 | egrep "^[ ]*\<[^ ]*\>[ ]*\<[^ ]*\>[ ]*\<shalom\>"
     ab   cd  shalom
     ab   cd  shalom 123

basicsys@mars~/lec7>echo "abbddd   fff34a" | egrep "^([a-z]).*\1$"
abbddd   fff34a

basicsys@mars~/lec7>echo "abbddd   fff34a " | egrep "^([a-z]).*\1$"

basicsys@mars~/lec7>

basicsys@mars~/lec7>echo "%bbddd   fff34%" | egrep "^(.).*\1$"
%bbddd   fff34%

basicsys@mars~/lec7>echo "abc123abc123" | egrep "^(.*)\1$"
abc123abc123

basicsys@mars~/lec7>echo "" | egrep "^(.*)\1$"

basicsys@mars~/lec7>echo "" | egrep "^(.+)\1$"

basicsys@mars~/lec7>

basicsys@mars~/lec7>echo "abc123abc123a" | egrep "^((.).*)\1\2$"
abc123abc123a

basicsys@mars~/lec7>echo "abc123abc123" | egrep "^((.).*)\1\2$"

basicsys@mars~/lec7>echo "abc123rabc123" | egrep "^((.).*)\1\2$"

basicsys@mars~/lec7>cat F1
123
abc
def
abbbab

basicsys@mars~/lec7>egrep ab F1
abc
abbbab

basicsys@mars~/lec7>egrep -c ab F1
2

basicsys@mars~/lec7>egrep -v ab F1
123
def

basicsys@mars~/lec7>egrep -v abc F1
123
def
abbbab

basicsys@mars~/lec7>egrep -v -c abc F1
3

basicsys@mars~/lec7>egrep -l abc F1
F1

basicsys@mars~/lec7>cat F1
123
abc
def
abbbab

basicsys@mars~/lec7>cat F2
abv
abc
eee

basicsys@mars~/lec7>egrep a F1 F2
F1:abc
F1:abbbab
F2:abv
F2:abc

basicsys@mars~/lec7>egrep -h a F1 F2
abc
abbbab
abv
abc

basicsys@mars~/lec7>egrep -c a F1 F2
F1:2
F2:2

basicsys@mars~/lec7>egrep -c -h a F1 F2
2
2

basicsys@mars~/lec7>grep -E -c -h a F1 F2
2
2

basicsys@mars~/lec7>

basicsys@mars~/lec7>mkdir t

basicsys@mars~/lec7>echo "I am a1" >|t/a1

basicsys@mars~/lec7>mkdir t/ad1

basicsys@mars~/lec7>echo "I am ad1/f1" >|t/ad1/f1

basicsys@mars~/lec7>echo "I am ad1/f2" >|t/ad1/f2

basicsys@mars~/lec7>mkdir t/fd1

basicsys@mars~/lec7>echo "I am fd1/a3" >|t/fd1/a3

basicsys@mars~/lec7>mkdir t/fd1/fd2

basicsys@mars~/lec7>echo "I am fd1/fd2/f3" >|t/fd1/fd2/f3

basicsys@mars~/lec7>cd t

basicsys@mars~/lec7/t>find . -name 'f*'
./fd1
./fd1/fd2
./fd1/fd2/f3
./ad1/f2
./ad1/f1

basicsys@mars~/lec7/t>cd ..

basicsys@mars~/lec7>find t -name 'f*'
t/fd1
t/fd1/fd2
t/fd1/fd2/f3
t/ad1/f2
t/ad1/f1

basicsys@mars~/lec7>find ~/lec7/t -name 'f*'
/home/cs/segel/basicsys/lec7/t/fd1
/home/cs/segel/basicsys/lec7/t/fd1/fd2
/home/cs/segel/basicsys/lec7/t/fd1/fd2/f3
/home/cs/segel/basicsys/lec7/t/ad1/f2
/home/cs/segel/basicsys/lec7/t/ad1/f1

basicsys@mars~/lec7/t>find . -size 8c
./a1

basicsys@mars~/lec7/t>find . -name 'f*' -type f
./fd1/fd2/f3
./ad1/f2
./ad1/f1

basicsys@mars~/lec7/t>find . -exec echo I am {} \;
I am .
I am ./fd1
I am ./fd1/fd2
I am ./fd1/fd2/f3
I am ./fd1/a3
I am ./a1
I am ./ad1
I am ./ad1/f2
I am ./ad1/f1

basicsys@mars~/lec7/t>cat P1

#!/bin/bash
echo "$1"|tr "/" "\n" | tail -1

basicsys@mars~/lec7/t>P1 d1/d2/d3
d3

basicsys@mars~/lec7/t>find . -exec P1 {} \;
.
P1
fd1
fd2
f3
a3
a1
ad1
f2
f1

The following program P1 scan the files in the directory 
in which P1 runs (at any depth inside the directory)
and for every file whose name repeats at least twice
in the directory gives the user an option to remove it. 

The program uses another program called get_file_name
which is shown below. 

basicsys@mars~/lec7>cat P1
#!/bin/bash
find . -type f -exec get_file_name {} \; >| tmp
cat tmp | sort | uniq -d >| tmp1
 for x in $(cat tmp1)
  do
   find . -name "$x" -ok rm {} \;
  done

basicsys@mars~/lec7>cat get_file_name
#!/bin/bash
echo $* | tr "/" "\n" | tail -1