How to add 100 spaces at end of each line of a file in Unix

Question

I have a file which is supposed to contain 200 characters in each line. I received a source file with only 100 characters in each line. I need to add 100 extra white spaces

Answer 1

Updated after Glenn's suggestion

Somewhat how Glenn suggests in the comments, the substitution is unnecessary, you can just add the spaces - although, taking that logic further, you don't even need the addition, you can just say them after the original line.

perl -nlE 'say $_," "x100' file

Original Answer

With Perl:

perl -pe 's/$/" " x 100/e' file

That says... "Substitute (s) the end of each line ($) with the calculated expression (e) of 100 repetitions of a space".

If you wanted to pad all lines to, say, 200 characters even if the input file was ragged (all lines of differing length), you could use something like this:

perl -pe '$pad=200-length;s/$/" " x $pad/e'

which would make up lines of 83, 102 and 197 characters to 200 each.