How to sort a file in-place
You can use file redirection to redirected the sorted output:
sort input-file > output_file
Or you can use the -o, --output=FILE option of sort to indicate the same input and output file:
sort -o file file
Without repeating the filename (with bash brace expansion)
sort -o file{,}
⚠️ Note: A common mistake is to try to redirect the output to the same input file
(e.g. sort file > file). This does not work as the shell is making the redirections (not the sort(1) program) and the input file (as being the output also) will be erased just before giving the sort(1) program the opportunity of reading it.
The sort command prints the result of the sorting operation to standard output by default. In order to achieve an "in-place" sort, you can do this:
sort -o file file
This overwrites the input file with the sorted output. The -o switch, used to specify an output, is defined by POSIX, so should be available on all version of sort:
-o Specify the name of an output file to be used instead of the standard output. This file can be the same as one of the input files.
If you are unfortunate enough to have a version of sort without the -o switch (Luis assures me that they exist), you can achieve an "in-place" edit in the standard way:
sort file > tmp && mv tmp file
sort file | sponge file
This is in the following Fedora package:
moreutils : Additional unix utilities
Repo : fedora
Matched from:
Filename : /usr/bin/sponge
Here's an approach which (ab)uses vim:
vim -c :sort -c :wq -E -s "${filename}"
The -c :sort -c :wq portion invokes commands to vim after the file opens. -E and -s are necessary so that vim executes in a "headless" mode which doesn't draw to the terminal.
This has almost no benefits over the sort -o "${filename}" "${filename}" approach except that it only takes the filename argument once.
This was useful for me to implement a formatter directive in a nanorc entry for .gitignore files. Here's what I used for that:
syntax "gitignore" "\.gitignore$"
formatter vim -c :sort -c :wq -E -s