sorting a file without using temporary files

Question

I want to sort a file in unix shell. Can I redirect my result into my input file?

e.g. if my input file is foo then can I use

    sort foo > foo   

or I should use:

    sort -o foo foo

What would be difference between above two?

Thanks,

Answer 1

Use

sort -o foo foo

From the man page:

-o OUTPUT-FILE' Write output to OUTPUT-FILE instead of standard output. If OUTPUT-FILE is one of the input files,sort' copies it to a temporary file before sorting and writing the output to OUTPUT-FILE.

sort foo > foo means writing output to the standard output which is redirected to the output file. Before redirecting, > will truncate/overwrite the output file if one is exist. Since both the input and output files are same, you will lose the input file information.