bash - paste not running from script but working on command line

I'm running this one liner as part of a larger script-

paste -d '' <(cut -c"1-5" file1) <(cut -c"1-2" file2) <(cut -c"8-" file1)

This takes the first 5 characters of the first file file1, the characters 1-2 of file2 and then the characters 8 onwards of file1 and pastes them all together.

$cat file1
1234567890
1234567890
1234567890
1234567890
1234567890

$cat file2
abcdefghij
abcdefghij

abcdefghij
abcdefghij
abcdefghij

output-
12345ab890
12345ab890
12345ab890
12345ab890
12345ab890

This works perfectly as expected from the command line (output shown above).

However if I put that line into a script (shown here)-

$cat a.sh

#!/bin/bash
paste -d '' <(cut -c"1-5" a) <(cut -c"1-2" b) <(cut -c"8-" a)

If I run the script I get this error-

$sh a.sh
a.sh: line 2: syntax error near unexpected token `('
a.sh: line 2: `paste -d '' <(cut -c"1-5" a) <(cut -c"1-2" b) <(cut -c"8-" a)'

Any ideas what is going wrong here? I ran it through shellcheck and it told me the script was fine.

Answer

run as below;

./a.sh 

or

bash a.sh

bash and sh are two different shells. bash is with more features and better syntax.