C:\test>type a.txt
A00001
A00002
A00003
A00004
A00005
A00006
A00007
A00008
A00009
A00010

C:\test>type b.txt
B00001
B00002
B00003
B00004
B00005
B00006
B00007
B00008
B00009
B00010

C:\test>perl -nle"printf qq[%10s\t%10s], $_, scalar <STDIN>" a.txt <b.txt
    A00001         B00001
    A00002         B00002
    A00003         B00003
    A00004         B00004
    A00005         B00005
    A00006         B00006
    A00007         B00007
    A00008         B00008
    A00009         B00009
    A00010         B00010