Unique sorting: Redirect output to the same file

Solution 1:

You can use sponge from moreutils package:

LC_ALL=C sort -u filename | sponge filename

You also don't need pipe to uniq, since when sort has -u option to unique lines when sorting.

Note that on GNU system with UTF-8 locales, sort -u or sort | uniq didn't give you unique lines, but the first from sequence of lines which sort the same in current locale.

$ printf '%b\n' '\U2460' '\U2461' | LC_ALL=en_US.utf8 sort | LC_ALL=en_US.utf8 uniq
①

gave you only ①. Changing locale to C force the sorting order based on the byte values:

$ export LC_ALL=C
$ printf '%b\n' '\U2460' '\U2461' | LC_ALL=C sort | LC_ALL=C uniq
①
②

Solution 2:

You don't need any extra command like cat and uniq and also without using rm command and mv command to removing and renaming the filename. just use simple command.

sort -u filename -o filename

 -u, --unique
        with -c, check for strict ordering; without -c, output only  the
        first of an equal run

 -o, --output=FILE
        write result to FILE instead of standard output

How it work?

sort command sorts your filename and with -u option, removes duplicate lines from it. then with -o option writes the output to the same file with in place method.