Print two files in two columns

With single pr command:

pr -Tm file[12]

-T (--omit-pagination) - omit page headers and trailers, eliminate any pagination by form feeds set in input files
-m (--merge) - print all files in parallel, one in each column

What about paste file{1,2}| column -s $'\t' -tn?

looooooooong line line  hello
line                    world

This is telling column to use Tab as columns' separator where we takes it from the paste command which is the default seperator there if not specified; generally:

paste -d'X' file{1,2}| column -s $'X' -tn

where X means any single character. You need to choose the one which granted that won't be occur in your files.
The -t option is used to determine the number of columns the input contains.
This will not add long tab between two files while other answers does.
this will work even if there was empty line(s) in file1 and it will not print second file in print area of file1, see below input/ouput

Input file1:
```
looooooooong line

line
```
Input file2:
```
hello
world
```
Output:
```
looooooooong line  hello
                   world
line
```

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