print the half right pyramid abcd pattern using loop in shell script-CodePudding

 A
 AB
 ABC
 ABCD
 ABCDE

read -p "Enter rows:" rows
for((i=1; i<=rows; i  ))
do
for((j=1; j<=i; j  ))
do
echo -n 'a'   
done
echo
done

not able to print the above pattern uses for loop but not getting how to print the abcd pattern.

CodePudding user response：

You could use two printfs to convert ASCII values to characters:

read -p "Enter rows:" rows
for ((i=1; i<=rows; i  )); do
  for ((j=1; j<=i; j  )); do
    printf "\x$(printf %x $((64 j)))"
  done
  echo
done

If you want to stay with echo -n you could use an array initialized with all letters and reference it by index:

abc=({A..Z})
read -p "Enter rows:" rows
for ((i=1; i<=rows; i  )); do
  for ((j=0; j<i; j  )); do
    echo -n ${abc[j]}
  done
  echo
done

CodePudding user response：

bash parameter expansions comprise the ${parameter:offset:length} substring expansion:

$ str="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
$ read -p "Enter rows:" rows
Enter rows:5
$ for (( i = 1; i <= rows; i   )); do echo "${str:0:i}"; done
A
AB
ABC
ABCD
ABCDE

Note: of course if you enter a value greater than 26 the extra output lines will be truncated to 26 characters.

Note: instead of assigning str manually you can compute it with:

$ arr=({A..Z}); str="${arr[*]}"; str="${str// }"
$ echo "$str"
ABCDEFGHIJKLMNOPQRSTUVWXYZ

This uses brace expansion {A..Z} to construct the array arr of uppercase letters, and pattern substitution ${str// } to remove the intermediate spaces in the expansion of the array ${arr[*]}. This is handy and less error prone. If you would like to add lower case letters and digits:

$ arr=({A..Z} {a..z} {0..9}); str="${arr[*]}"; str="${str// }"
$ echo "$str"
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789

CodePudding user response：

for((i=1; i<=rows; i  ))
do
for((j=1; j<=i; j  ))
do
printf '%x' $(expr 96   $j) | xxd -p -r
done
echo
done

I've converted ascii 97-->'a' to hex format and than decoded to that char value.

So what is happening here:

 printf '%x' $(expr 96   $j)

will print the numbers like

Now we know that \x61 --> 'a'. We want to convert this hex \x61 to a char. So by using -r we are telling xxd to convert it from hex to ascii and by using -p we are telling xxd that out hex is a continous string not like x61x62x63 but 616263.

Hope it helps.