basicsys@mars~/lec10>expr match ababcdcde '\(\(ab\)\+\(cd\)\+\)'
ababcdcd

basicsys@mars~/lec10>expr match ababcdcde '\(\(ab\)\+\)\(cd\)\+'
abab

basicsys@mars~/lec10>expr index abcde db
2

basicsys@mars~/lec10>expr index abcde rc
3

basicsys@mars~/lec10>expr index abcde rt
0

basicsys@mars~/lec10>expr substr abcdefg 3 4
cdef

basicsys@mars~/lec10>expr substr abcdefg 3 7
cdefg

basicsys@mars~/lec10>expr substr abcdefg -1 1

basicsys@mars~/lec10>expr substr abcdefg 0 1

basicsys@mars~/lec10>expr substr abcdefg 10 1

basicsys@mars~/lec10>expr substr abcdefg 3
expr: syntax error

basicsys@mars~/lec10>expr substr abcdefg 3 3
cde

basicsys@mars~/lec10>x=abcdefg

basicsys@mars~/lec10>echo ${x:3:4}
defg

basicsys@mars~/lec10>echo ${x:3}
defg

basicsys@mars~/lec10>echo ${x:2}
cdefg

basicsys@mars~/lec10>y=${x:2}

basicsys@mars~/lec10>echo "$y"
cdefg

basicsys@mars~/lec10>echo ${x#a??}
defg

basicsys@mars~/lec10>echo ${x#a*}
bcdefg

basicsys@mars~/lec10>echo ${x##a*}

basicsys@mars~/lec10>echo ${x%e*}
abcd

basicsys@mars~/lec10>x=fabcdab

basicsys@mars~/lec10>echo ${x%ab*}
fabcd

basicsys@mars~/lec10>echo ${x%%ab*}
f

basicsys@mars~/lec10>x=ababcdab

basicsys@mars~/lec10>echo ${x/ab/zzz}
zzzabcdab

basicsys@mars~/lec10>echo ${x//ab/zzz}
zzzzzzcdzzz

basicsys@mars~/lec10>echo ${x/ab*/zzz}
zzz

basicsys@mars~/lec10>rev F1
cba

basicsys@mars~/lec10>echo abc | rev
cba

basicsys@mars~/lec10>cat G1
#!/bin/bash
echo -n "" >|tmp
x=$(pwd)
for y in $(find $x -type f)
 do
  echo ${y##*/}${y} >> tmp
 done
sort tmp >| tmp1
for z in $(cat tmp1)
  do
   echo \/${z#*/}
  done

basicsys@mars~/lec10>G1 | more
/home/cs/segel/basicsys/lec10/F1
/home/cs/segel/basicsys/lec10/oldlec10/F1
/home/cs/segel/basicsys/lec10/F2
/home/cs/segel/basicsys/lec10/oldlec10/F2
/home/cs/segel/basicsys/lec10/F3
/home/cs/segel/basicsys/lec10/oldlec10/F3
/home/cs/segel/basicsys/lec10/F3t
/home/cs/segel/basicsys/lec10/F4
/home/cs/segel/basicsys/lec10/oldlec10/F4
/home/cs/segel/basicsys/lec10/F
/home/cs/segel/basicsys/lec10/G1
/home/cs/segel/basicsys/lec10/H
/home/cs/segel/basicsys/lec10/H.rep
/home/cs/segel/basicsys/lec10/lec10e.txt
/home/cs/segel/basicsys/lec10/lec10m.txt
/home/cs/segel/basicsys/lec10/oldlec10/lec10.
/home/cs/segel/basicsys/lec10/oldledc10e
/home/cs/segel/basicsys/lec10/oldlec10/P1
/home/cs/segel/basicsys/lec10/P1
/home/cs/segel/basicsys/lec10/oldlec10/P2
/home/cs/segel/basicsys/lec10/tmp1
/home/cs/segel/basicsys/lec10/tmp

basicsys@mars~/lec10>y=/home/cs/segel/basicsys/lec10/tmp1

basicsys@mars~/lec10>echo $y
/home/cs/segel/basicsys/lec10/tmp1

basicsys@mars~/lec10>echo ${y##*/}${y}
tmp1/home/cs/segel/basicsys/lec10/tmp1

basicsys@mars~/lec10>echo a{b,c}e
abe ace

basicsys@mars~/lec10>echo a{b,c}{1,2,3}r
ab1r ab2r ab3r ac1r ac2r ac3r

basicsys@mars~/lec10>for x in {1..10}; do echo $x ; done
1
2
3
4
5
6
7
8
9
10

basicsys@mars~/lec10>for x in $(seq 10); do echo $x ; done
1
2
3
4
5
6
7
8
9
10

basicsys@mars~/lec10>echo {1..10}
1 2 3 4 5 6 7 8 9 10

basicsys@mars~/lec10>echo {1..10..2}
{1..10..2}

basicsys@mars~/lec10>echo {3..10}
3 4 5 6 7 8 9 10

basicsys@mars~/lec10>echo {c h}
{c h}

basicsys@mars~/lec10>echo {c..h}
c d e f g h

basicsys@mars~/lec10>x=3

basicsys@mars~/lec10>y=8

basicsys@mars~/lec10>echo {$x..$y}
{3..8}

basicsys@mars~/lec10>echo "{$x..$y}"
{3..8}

basicsys@mars~/lec10>echo \{$x..$y\}
{3..8}

basicsys@mars~/lec10>eval echo {$x..$y}
3 4 5 6 7 8

basicsys@mars~/lec10>echo $(echo {$x..$y})
{3..8}

basicsys@mars~/lec10>a=20

basicsys@mars~/lec10>echo $a
20

basicsys@mars~/lec10>a=(20 30 40)

basicsys@mars~/lec10>echo $a
20

basicsys@mars~/lec10>echo ${a[0]}
20

basicsys@mars~/lec10>echo ${a[1]}
30

basicsys@mars~/lec10>echo ${a[2]}
40

basicsys@mars~/lec10>echo ${a[@]}
20 30 40

basicsys@mars~/lec10>echo "${a[@]}"
20 30 40

basicsys@mars~/lec10>a=("ab  10" "cd   20" 40)

basicsys@mars~/lec10>echo "${a[@]}"
ab  10 cd   20 40

basicsys@mars~/lec10>echo ${a[@]}
ab 10 cd 20 40

basicsys@mars~/lec10>a[1]="40 1111"

basicsys@mars~/lec10>echo "${a[@]}"
ab  10 40 1111 40

basicsys@mars~/lec10>b=({2..5}{a..c})

basicsys@mars~/lec10>echo "${b[@]}"
2a 2b 2c 3a 3b 3c 4a 4b 4c 5a 5b 5c

basicsys@mars~/lec10>echo "${#b[@]}"
12

basicsys@mars~/lec10>echo "${#a[@]}"
3

basicsys@mars~/lec10>echo ${#a[@]}
3

basicsys@mars~/lec10>echo ${#a[@]}
3

basicsys@mars~/lec10>echo ${a[@]}
ab 10 40 1111 40

basicsys@mars~/lec10>echo "${b[@]}"
2a 2b 2c 3a 3b 3c 4a 4b 4c 5a 5b 5c

basicsys@mars~/lec10>echo "${b[@]:2:3}"
2c 3a 3b

basicsys@mars~/lec10>b=({a..c}{1..2}{d..f})

basicsys@mars~/lec10>echo "${b[@]}"
a1d a1e a1f a2d a2e a2f b1d b1e b1f b2d b2e b2f c1d c1e c1f c2d c2e c2f

basicsys@mars~/lec10>echo ${#b[@]}
18

basicsys@mars~/lec10>echo ${#b}
3

basicsys@mars~/lec10>echo ${b}
a1d

basicsys@mars~/lec10>echo ${b[@]/#?}
1d 1e 1f 2d 2e 2f 1d 1e 1f 2d 2e 2f 1d 1e 1f 2d 2e 2f

basicsys@mars~/lec10>echo ${b[@]/%?}
a1 a1 a1 a2 a2 a2 b1 b1 b1 b2 b2 b2 c1 c1 c1 c2 c2 c2

basicsys@mars~/lec10>echo ${b[@]/%%?}
a1d a1e a1f a2d a2e a2f b1d b1e b1f b2d b2e b2f c1d c1e c1f c2d c2e c2f

basicsys@mars~/lec10>echo ${b[@]/a/zzz}
zzz1d zzz1e zzz1f zzz2d zzz2e zzz2f b1d b1e b1f b2d b2e b2f c1d c1e c1f c2d c2ec2f

basicsys@mars~/lec10>b=({a..c}1{a..c})

basicsys@mars~/lec10>echo ${b[@]}
a1a a1b a1c b1a b1b b1c c1a c1b c1c

basicsys@mars~/lec10>echo ${b[@]/a/zzz}
zzz1a zzz1b zzz1c b1zzz b1b b1c c1zzz c1b c1c

basicsys@mars~/lec10>echo ${b[@]//a/zzz}
zzz1zzz zzz1b zzz1c b1zzz b1b b1c c1zzz c1b c1c


Look at the array-string example at the course web site