How to create 100 files with the names a1, a2, a3, .... a100 in the terminal?

the greatest “complexity” is to get a sequence of numbers. to add them with letters and hand them over to the touch program is simple.

As far as I know, the posix standard does not have any “onboard” tools that simplify the generation process. You can use some universal language:

1. using the awk program:

    $ awk 'BEGIN { for(i=1;i<=5;i++) printf "a%d\n", i }' a1 a2 a3 a4 a5 

   to create files, just transfer the list to the touch program:

    $ touch $(awk 'BEGIN { for(i=1;i<=5;i++) printf "a%d\n", i }') 

2. using the bc program:

    $ echo 'for (i=1; i<=5; i++) {print "a",i,"\n"}' | bc a1 a2 a3 a4 a5 

   to create files, just transfer the list to the touch program:

    $ touch $(echo 'for (i=1; i<=5; i++) {print "a",i,"\n"}' | bc) 

3. in the gnu operating system, there is a seq program that just simplifies the generation:

    $ seq -f 'a%g' 1 5 a1 a2 a3 a4 a5 

   to create files, just transfer the list to the touch program:

    $ touch $(seq -f 'a%g' 1 5) 

4. well, modern “heaped” bash / zsh shells understand the {1..5} construct:

    $ echo {1..5} 1 2 3 4 5 

   those. you can create files again by passing the list to the touch program:

    $ touch a{1..5}