Coding Bash vs. Perl vs. Python (by Evan Liu)

#1.Create an array
arr=("hatter" "duchess" "alice")

#2.Print the array length
echo ${#arr[*]}
echo ${#arr[@]}

-------output----------

#1.Create an array

#2.Print the array length
3
3

#1.Create an array
@arr=("hatter","duchess","alice");

#2.Print the array length
print 0+@arr."\n";
print scalar(@arr)."\n";
print 1+$#arr."\n";

-------output----------

#1.Create an array

#2.Print the array length
3
3
3

#1.Create an array
arr=["hatter","duchess","alice"];

#2.Print the array length
print len(arr);

-------output----------

#1.Create an array 

#2.Print the array length 
3

#1.Create an array
arr=({1..4}); #or
arr=(1 2 3 4)

#2.Print all elements
echo ${arr[@]}  #or
echo ${arr[*]}

#3.Print elements at index 0~2 respectively
echo ${arr[0]} ${arr[1]} ${arr[3]}

#4.Print two consecutive elements start from index 0
echo ${arr[@]:0:2}

#5.Print elements starting with index 2
echo ${arr[*]:2}

#6.Print the last element
echo ${arr[-1]}   #or
echo ${arr[${#arr[@]}-1]}


-------output----------

#1.Create an array

#2.Print all elements
1 2 3 4
1 2 3 4

#3.Print elements at index 0~2 respectively
1 2 4

#4.Print two consecutive elements start from index 0
1 2

#5.Print elements starting with index 2
3 4

#6.Print the last element
4
4

#1.Create an array
@arr=(1 .. 4);  #or
@arr=(1,2,3,4);

#2.Print all elements
print "@arr\n";  #or
print join(" ",@arr)."\n";

#3.Print elements at index 0~2 respectively
print "$arr[0] $arr[1] $arr[3]\n";

#4.Print two consecutive elements start from index 0
print "@arr[0 .. 1]\n";

#5.Print elements starting with index 2
print "@arr[2 .. $#arr]\n";

#6.Print the last element
print "@arr[-1]\n"; #or
print "@arr[$#arr]";

-------output----------

#1.Create an array

#2.Print all elements
1 2 3 4
1 2 3 4

#3.Print elements at index 0~2 respectively
1 2 4

#4.Print two consecutive elements start from index 0
1 2

#5.Print elements starting with index 2
3 4

#6.Print the last element
4
4

#1.Create an array
arr=range(1,5)

#2.Print all elements
arr    #or
for i in arr: print i,
print

#3.Print elements at index 0~2 respectively
print arr[0],arr[1],arr[3]

#4.Print two consecutive elements start from index 0
print arr[0:2]

#5.Print elements starting with index 2
print arr[2:]

#6.Print the last element
print arr[-1]

-------output----------

#1.Create an array 

#2.Print all elements 
1 2 3 4

#3.Print elements at index 0~2 respectively 
1 2 4

#4.Print two consecutive elements start from index 0 
[1, 2]

#5.Print elements starting with index 2 
[3, 4]

#6.Print the last element 
4

#1.Create an array with three elements
arr=("hatter" "duchess" "alice")
declare -p arr

#2.Iterate over the array
#  use for loop
for i in "${arr[@]}"; do echo -n "$i "; done; echo
#  use c style for loop
for ((i=0;i<${#arr[@]};i++)); do echo -n "${arr[$i]} "; done


-------output----------

#1.Create an array with three elements
declare -a arr='([0]="hatter" [1]="duchess" [2]="alice")'

#2.Iterate over the array
#  use for loop
hatter duchess alice 
#  use c style for loop
hatter duchess alice

#1.Create an array with three elements
@arr=("hatter","duchess","alice");
#  or
@arr=qw(hatter duchess alice);

#2.Iterate over the array
print "$_ " foreach (@arr);

-------output----------

#1.Create an array with three elements
#  or

#2.Iterate over the array
hatter duchess alice

#1.Create an array with three elements
arr=["hatter","duchess","alice"]
#  tuple is immutable,and faster than list
tpl=("hatter","duchess","alice")

#2.Iterate over the array
for i in arr: print(i),
print
for i in tpl: print i,

-------output----------

#1.Create an array with three elements 
#  tuple is immutable,and faster than list 

#2.Iterate over the array 
hatter duchess alice
hatter duchess alice

#1.Create a array
arr=("hatter" "duchess" "alice")

#2.Get the index of the element with value 'duchess'
for ((i=0;i<${#arr[@]};i++));do 
  [[ ${arr[$i]} = 'duchess' ]] && echo $i
done
#  or use associative array
declare -A ass; 
ass=([hatter]=0 [duchess]=1 [alice]=2); 
echo ${ass[duchess]}

-------output----------

#1.Create a array

#2.Get the index of the element with value 'duchess'
1
#  or use associative array
1

#1.Create a array
@arr=("hatter","duchess","alice");

#2.Get the index of the element with value 'duchess'
#  use index hash
my %index;
@index{@arr}=(0..$#arr);
print $index{"duchess"}."\n";
#  or use List::MoreUtils
use List::MoreUtils qw(first_index);
print first_index {$_ eq 'duchess'} @arr;

-------output----------

#1.Create a array

#2.Get the index of the element with value 'duchess'
#  use index hash
1
#  or use List::MoreUtils
1

#1.Create a array
arr=["hatter","duchess","alice"]

#2.Get the index of the element with value 'duchess'
print arr.index('duchess')

-------output----------

#1.Create a array 

#2.Get the index of the element with value 'duchess' 
1

#1.Create a array
arr=("hatter" "duchess" "alice")

#2.Append a element to array
arr=(${arr[@]} rabbit)
echo ${arr[@]}
#  or use
arr+=("rabbit")
echo ${arr[@]}

-------output----------

#1.Create a array

#2.Append a element to array
hatter duchess alice rabbit
#  or use
hatter duchess alice rabbit rabbit

#1.Create a array
@arr=("hatter","duchess","alice");

#2.Append a element to array
@arr=(@arr,"rabbit");
print "@arr\n";
#  or use push
push(@arr,"rabbit");
print "@arr\n";

-------output----------

#1.Create a array

#2.Append a element to array
hatter duchess alice rabbit
#  or use push
hatter duchess alice rabbit rabbit

#1.Create a array
arr=["hatter","duchess","alice"]

#2.Append a element to array
arr=arr+['rabbit']
print arr
#  or use unction insert
arr.insert(len(arr),"rabbit")
print arr

-------output----------

#1.Create a array 

#2.Append a element to array 
['hatter', 'duchess', 'alice', 'rabbit']
#  or use unction insert 
['hatter', 'duchess', 'alice', 'rabbit', 'rabbit']

pos=1
#1.Create a array
arr=("hatter" "duchess" "alice")

#2.Insert a element to array
arr=(${arr[@]:0:$pos} 'rabbit' ${arr[@]:$pos})
echo ${arr[@]}

-------output----------

#1.Create a array

#2.Insert a element to array
hatter rabbit duchess alice

$pos=1;
#1.Create a array
@arr=("hatter","duchess","alice");

#2.Insert a element to array
splice @arr,$pos,0,"rabbit";
print "@arr\n";

-------output----------

#1.Create a array

#2.Insert a element to array
hatter rabbit duchess alice

pos=1
#1.Create a array
arr=["hatter","duchess","alice"]

#2.Insert a element to array
arr.insert(pos,"rabbit")
print arr

-------output----------

#1.Create a array 

#2.Insert a element to array 
['hatter', 'rabbit', 'duchess', 'alice']

#1.Create an array
arr=("hatter" "duchess" "alice")

#2.Remove the 2nd element
#  assigning null to the 2nd element
unset arr[1]
echo "\${arr[@]} -->${arr[@]}"
echo "\${arr[1]} -->${arr[1]}"

#3.Alternative ways to remove an element
arr=("hatter" "duchess" "alice")
pos=1
arr=(${arr[@]:0:$pos} ${arr[@]:$(($pos+1))})
echo "\${arr[@]} -->${arr[@]}"
echo "\${arr[1]} -->${arr[1]}"

-------output----------

#1.Create an array

#2.Remove the 2nd element
#  assigning null to the 2nd element
${arr[@]} -->hatter alice
${arr[1]} -->

#3.Alternative ways to remove an element
${arr[@]} -->hatter alice
${arr[1]} -->alice

#1.Create an array
@arr=("hatter","duchess","alice");

#2.Remove the 2nd element
delete $arr[1];
print "\@arr -->@arr\n";
print "\$arr[1] -->$arr[1]\n";

#3.Alternative ways to remove an element
@arr=("hatter","duchess","alice");
#  splice arr_name, pos, del_len, arr_insert
splice @arr,1,1;
print "\@arr -->@arr\n";
print "\$arr[1] -->$arr[1]\n";

-------output----------

#1.Create an array

#2.Remove the 2nd element
@arr -->hatter  alice
$arr[1] -->

#3.Alternative ways to remove an element
#  splice arr_name, pos, del_len, arr_insert
@arr -->hatter alice
$arr[1] -->alice

#1.Create an array
arr=["hatter","duchess","alice"]

#2.Remove the 2nd element
del arr[1];
print "arr -->", arr
print "arr[1] -->", arr[1]

#3.Alternative ways to remove an element
arr=["hatter","duchess","alice"]
#  from 1 to 2(not included) replaced 
arr[1:2]=[]
print "arr -->", arr
print "arr[1] -->", arr[1]
#  or use function pop 
arr=["hatter","duchess","alice"]
arr.pop(1)
print "arr -->", arr
print "arr[1] -->", arr[1]

-------output----------

#1.Create an array 

#2.Remove the 2nd element 
arr --> ['hatter', 'alice']
arr[1] --> alice

#3.Alternative ways to remove an element 
#  from 1 to 2(not included) replaced  
arr --> ['hatter', 'alice']
arr[1] --> alice
#  or use function pop  
arr --> ['hatter', 'alice']
arr[1] --> alice

#1.Create a array
arr=("hatter" "duchess" "duchess" "alice")

#2.Remove all elements with value of "duchess"
arr=(${arr[@]/duchess/})
echo ${arr[@]}

-------output----------

#1.Create a array

#2.Remove all elements with value of duchess
hatter alice

use feature ":5.10";
#1.Create a array
@arr=("hatter","duchess","duchess","alice");

#2.Remove all elements with value of "duchess"
#  use grep
@arr2=grep { $_ ne "duchess" } @arr;
say "@arr2";
@arr3=grep ! /duchess/, @arr;
say "@arr3";
#  or use map
@arr4=map { $_ eq 'duchess'?():$_} @arr;
say "@arr4";


-------output----------

#1.Create a array

#2.Remove all elements with value of "duchess"
#  use grep
hatter alice
hatter alice
#  or use map
hatter alice

#1.Create a array
arr=["hatter","duchess","duchess","alice"]

#2.Remove all elements with value of "duchess"
#  use remove function
while 'duchess' in arr: arr.remove('duchess') 
print arr
arr=["hatter","duchess","duchess","alice"]
#  or use list
print [i for i in arr if i != 'duchess']
#  or use filter and lambda
print filter(lambda x: x != "duchess", arr)


-------output----------

#1.Create a array 

#2.Remove all elements with value of "duchess" 
#  use remove function 
['hatter', 'alice']
#  or use list 
['hatter', 'alice']
#  or use filter and lambda 
['hatter', 'alice']

#1.Create a array
arr=("hatter" "duchess" "duchess" "alice")

#2.Remove "duchess" with "hare" for all elements
echo ${arr[@]/duchess/hare}

-------output----------

#1.Create a array

#2.Remove duchess with hare for all elements
hatter hare hare alice

use feature ":5.10";
#1.Create a array
@arr1=@arr2=@arr3=("hatter","duchess","duchess","alice");

#2.Remove "duchess" with "hare" for all elements
#  use for loop
s/duchess/hare/ for @arr1;
say "@arr1";
#  or use map
map {s/duchess/queen/g;} @arr2;
say "@arr2";
#  or use map 
@arr3=map { $_ eq 'duchess' ? 'turtle':$_} @arr3;
say "@arr3";

-------output----------

#1.Create a array

#2.Remove "duchess" with "hare" for all elements
#  use for loop
hatter hare hare alice
#  or use map
hatter queen queen alice
#  or use map 
hatter turtle turtle alice

#1.Create a array
arr1=arr2=["hatter","duchess","duchess","alice"]

#2.Remove "duchess" with "hare" for all elements
#  use for loop and enumerate
for n,i in enumerate(arr1):
    if i=="duchess":
        arr1[n]="hare"
print arr1
#  or use
arr2=["hare" if i=="duchess" else i for i in arr2]
print arr2

-------output----------

#1.Create a array 

#2.Remove "duchess" with "hare" for all elements 
#  use for loop and enumerate 
['hatter', 'hare', 'hare', 'alice']
#  or use 
['hatter', 'hare', 'hare', 'alice']

#1.Create a array
arr=("hatter" "duchess" "alice")

#2.Sort all the elements
IFS=$'\r\n' arr=(`for i in "${arr[@]}"; do echo  "$i"; done | sort`)
echo ${arr[@]}

-------output----------

#1.Create a array

#2.Sort all the elements
alice duchess hatter

#1.Create a array
@arr=("hatter","duchess","alice");

#2.Sort all the elements
@arr=sort @arr;
print "@arr";

-------output----------

#1.Create a array

#2.Sort all the elements
alice duchess hatter

#1.Create a array
arr=["hatter","duchess","alice"]

#2.Sort all the elements
arr.sort()
print arr

-------output----------

#1.Create a array 

#2.Sort all the elements 
['alice', 'duchess', 'hatter']

#1.Create a array
arr=("hatter" "duchess" "alice")

#2.Reverse all the elements
arr=(`for ((i=${#arr[@]}-1; i>=0; i--)); do echo "${arr[$i]}"; done`); 
echo ${arr[@]}

-------output----------

#1.Create a array

#2.Reverse all the elements
alice duchess hatter

#1.Create a array
@arr=("hatter","duchess","alice");

#2.Reverse all the elements
print join(" ",reverse(@arr));

-------output----------

#1.Create a array

#2.Reverse all the elements
alice duchess hatter

#1.Create a array
arr=["hatter","duchess","alice"]

#2.Reverse all the elements
arr.reverse()
print arr
#  or use slice functionality
print arr[::-1]

-------output----------

#1.Create a array 

#2.Reverse all the elements 
['alice', 'duchess', 'hatter']
#  or use slice functionality 
['hatter', 'duchess', 'alice']

#1.Create two arrays
arr1=("hatter" "duchess" "alice")
arr2=("rabbit" "hare")

#2.concatenate the two arrays
arr=("${arr1[@]}" "${arr2[@]}")
echo ${arr[@]}

-------output----------

#1.Create two arrays

#2.concatenate the two arrays
hatter duchess alice rabbit hare

#1.Create two arrays
@arr1=("hatter","duchess","alice");
@arr2=qw(rabbit hare);

#2.concatenate the two arrays
@arr = (@arr1 , @arr2);
print "@arr";

-------output----------

#1.Create two arrays

#2.concatenate the two arrays
hatter duchess alice rabbit hare

#1.Create two arrays
arr1=["hatter","duchess","alice"]
arr2=["rabbit","hare"]

#2.concatenate the two arrays
arr = arr1 + arr2
print arr

-------output----------

#1.Create two arrays 

#2.concatenate the two arrays 
['hatter', 'duchess', 'alice', 'rabbit', 'hare']

#1.Create a array
arr=("hatter" "duchess" "alice")

#2.Concatenate all elements to a string with '-'
IFS='-' 
echo "${arr[*]}"
unset IFS

-------output----------

#1.Create a array

#2.Concatenate all elements to a string with '-'
hatter-duchess-alice

#1.Create a array
@arr=("hatter","duchess","alice");

#2.Concatenate all elements to a string with '-'
print join('-', @arr);

-------output----------

#1.Create a array

#2.Concatenate all elements to a string with '-'
hatter-duchess-alice

#1.Create a array
arr=["hatter","duchess","alice"]

#2.Concatenate all elements to a string with '-'
print '-'.join(arr)

-------output----------

#1.Create a array 

#2.Concatenate all elements to a string with '-' 
hatter-duchess-alice