If statement for two different arrays in bash

Question

I have two arrays, which are arrAlpha[] and arrPT[]. Array arrAlpha contains the Alphabets and array arrPT[] contains some of the plain letters.following is the code that i wrote in bash shell script to compare elements of both arrays and to store the position elements of arrPT[] in arrAlpha[] to array arrT[]. But when i run i feel like something is wrong in if statement to print out the elements in arrT[]. can anyone help me please?

     #!/bin/bash

     arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)

     arrPT=(E K N R S W )
     lenPT=${#arrPT}
     declare -A arrT
     q=0
     for((i=0; i<lenPT; i++)) do
         for((j=i; j<26; j++)) do
             if [  ${arrPT[$i]}  =  ${arrAlpha[$j]}  ]; then
                 arrT[$q]=$j % 26;
                 ((++q));
             fi
          done
     done

     echo ${arrAlpha[@]}
     echo ${arrPT[@]}
     echo ${arrT[@]}

the expected output is to change elements arrPT to number 0 to 25.

    arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
    arrPT =(E K N R S W)
    arrT =(4 10 13 17 18 22)

What do you mean by "feel like something wrong" ? Did the output is not as you expected? — Avihoo Mamka
– Avihoo Mamka, Commented Aug 21, 2016 at 11:35
what i mean by feel like something is, i'm not sure about if statement that i wrote is correct or not. can u help me please? — Mohamed Nuzhy
– Mohamed Nuzhy, Commented Aug 21, 2016 at 12:11

pakistanprogrammerclub · Accepted Answer · 2016-08-21 12:30:50Z

1

Here's a fixed version of your script - there are some style changes that I prefer

arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
arrPT=(E K N R S W )
# array length needs index *
lenPT=${#arrPT[*]}
# seems arrT can be simple indexed array
declare -a arrT
q=0
for((i=0; i<lenPT; ++i)); do
  for((j=0; j<26; ++j)); do
    if [[ ${arrPT[i]} == ${arrAlpha[j]} ]]; then
# arithmetic inside $(())
      arrT[q++]=$((j % 26))
    fi
  done
done
echo ${arrAlpha[@]}
echo ${arrPT[@]}
echo ${arrT[@]}

answered Aug 21, 2016 at 12:30

pakistanprogrammerclub

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1 Comment

Charles Duffy Over a year ago

FYI, in [[ $foo == $bar ]], $bar is treated as a glob expansion unless quoted; if, for instance, it were *, it would match anything. If you don't want that behavior, consider quoting the right-hand side.

score 0 · Accepted Answer · 2016-08-21 17:43:47Z

The main bug is with this line:

lenPT=${#arrPT}

which should be written like:

lenPT=${#arrPT[@]}

But, in fact, there is no need (even if it is not wrong to use it) for such variable, change this line:

for((i=0; i<lenPT; i++)) do

to:

for((i=0; i<${#arrPT[@]}; i++)) do

Some other issues:

There is no need to mod 26 the value of $j, it will never reach 26.
The array arrT seems to be an indexed array: -a no need for -A.
There is no need for variable q if each result will be in the same position as the index i
Please quote your expansions.
Use printf (more reliable) instead of echo.

The script with all the above done is:

#!/bin/bash

 arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
 arrPT=(E K N R S W )

 declare -a arrT

 for((i=0; i<${#arrPT[@]}; i++)) do
    for((j=i; j<${#arrAlpha[@]}; j++)) do
       [[  ${arrPT[i]}  ==  "${arrAlpha[j]}"  ]] && let arrT[i]=j
    done
 done

 printf '%s ' "${arrAlpha[@]}"  ; echo 
 printf '%3s ' "${arrPT[@]}"    ; echo 
 printf '%3s ' "${arrT[@]}" ; echo

Of course, the second loop could be removed by cutting that string at the character:

#!/bin/bash

Alpha=ABCDEFGHIJKLMNOPQRSTUVWXYZ
arrPT=(E K N R S W )

declare -a arrT

for((i=0; i<${#arrPT[@]}; i++)) do
    arrT[i]=${Alpha%"${arrPT[i]}"*}    # cut the string at the character.
    arrT[i]=${#arrT[i]}                # Use the len of the cut string.
done

printf '%s ' "$Alpha"           ; echo 
printf '%3s ' "${arrPT[@]}" ; echo 
printf '%3s ' "${arrT[@]}"      ; echo

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