basicsys@mars~/lec2>ls
F1

basicsys@mars~/lec2>mkdir dir2

basicsys@mars~/lec2>ls
dir2  F1

basicsys@mars~/lec2>cd dir2

basicsys@mars~/lec2/dir2>ls

basicsys@mars~/lec2/dir2>echo abcd >| F2

basicsys@mars~/lec2/dir2>cat F2
abcd

basicsys@mars~/lec2/dir2>ls
F2

basicsys@mars~/lec2/dir2>mkdir dir3

basicsys@mars~/lec2/dir2>ls
dir3  F2
dir2  F1  lec2m.txt

basicsys@mars~/lec2>ls -R
.:
dir2  F1  lec2m.txt

./dir2:
dir3  F2

./dir2/dir3:

basicsys@mars~/lec2>mkdir dir2
mkdir: cannot create directory `dir2': File exists

basicsys@mars~/lec2>mkdir F1
mkdir: cannot create directory `F1': File exists

basicsys@mars~/lec2>mkdir d5/d6/d7
mkdir: cannot create directory `d5/d6/d7': No such file or

basicsys@mars~/lec2>mkdir -p d5/d6/d7

basicsys@mars~/lec2>ls
d5  dir2  F1  lec2m.txt

basicsys@mars~/lec2>ls -R
.:
d5  dir2  F1  lec2m.txt

./d5:
d6

./d5/d6:

./dir2:
dir3  F2

./dir2/dir3:

basicsys@mars~/lec2>mkdir -p d5/d6/d7/d8

basicsys@mars~/lec2>ls -R
.:
d5  dir2  F1  lec2m.txt

./d5:
d6

./d5/d6:
d7

./d5/d6/d7:
d8

./d5/d6/d7/d8:

./dir2:
dir3  F2

./dir2/dir3:

basicsys@mars~/lec2>rm dir2
rm: cannot remove `dir2': Is a directory

basicsys@mars~/lec2>rm F1

basicsys@mars~/lec2>ls
dir2  lec2m.txt

basicsys@mars~/lec2>rm -r F1

basicsys@mars~/lec2>ls
dir2  lec2m.txt
dir2  lec2m.txt

basicsys@mars~/lec2>echo abcd >|F1

basicsys@mars~/lec2>ls

dir2  F1  lec2m.txt

basicsys@mars~/lec2>rm F2
rm: cannot remove `F2': No such file or directory

basicsys@mars~/lec2>rm -f F2

basicsys@mars~/lec2>rm -i *
rm: cannot remove directory `dir2': Is a directory
rm: remove regular file `F1'? y
rm: remove regular file `lec2m.txt'? n

basicsys@mars~/lec2>ls
dir2  lec2m.txt

basicsys@mars~/lec2>rm -r -i dir2
rm: descend into directory `dir2'? y
rm: remove regular file `dir2/F2'? n
rm: remove directory `dir2/dir3'? n

basicsys@mars~/lec2>cat F1
abcd

basicsys@mars~/lec2>mv F1 dir2/F25

basicsys@mars~/lec2>ls
dir2  F2  lec2m.txt

basicsys@mars~/lec2>cd dir2

basicsys@mars~/lec2/dir2>cat F25
abcd

basicsys@mars~/lec2/dir2>ls
dir2  dir3  F2  F25

basicsys@mars~/lec2/dir2>mv F* dir3

basicsys@mars~/lec2/dir2>cat P2
#!/bin/bash
echo "enter first number: "
read x
echo "enter second number: "
read y
echo "the sum of the two numbers is: $[$x+$y]"

basicsys@mars~/lec2>P2
enter first number:
8
enter second number:
12
the sum of the two numbers is: 20

basicsys@mars~/lec2>P2 < F3
enter first number:
enter second number:
the sum of the two numbers is: 42

basicsys@mars~/lec2>cat P3
#!/bin/bash
sum=0
while read x
do
sum=$[$sum + $x]
done
echo "the sum is: $sum"
basicsys@mars~/lec2>P3
8
10
12
the sum is: 30

basicsys@mars~/lec2>seq 10 >|F3

basicsys@mars~/lec2>cat F3
1
2
3
4
5
6
7
8
9
10
basicsys@mars~/lec2>P3 < F3
the sum is: 55