Q:\>copy con test.txt
blah    a       blah
^Z
        1 file(s) copied.

Q:\>perl -w expand.pl test.txt
blah    a       blah

Q:\>perl -w expand.pl test.txt|perl -ple "s!\t!x!g"
blah    a       blah

Q:\>perl -w expand.pl test.txt|perl -ple "s! !_!g"
blah____a_______blah

Q:\>type test.txt|perl -ple "s! !_!g"
blah    a       blah