rewrite primerWhat it is
rewrite is a simple command-line utility that allows for the in-place rewrite of a file's contents, even where the file is being read from as the input. This makes transforming the contents of a file via other standard unix utilities dead simple, even when they expect the input and output files/streams to be physically separate.
The problem
You have a sequence of chained operations/commands that reads from a given file f, and you want to replace the contents of f with the result of that chain of commands. If you try to redirect the output of your script via something like > f or | tee f, you'll find that more often than not, you'll lose everything and corrupt your datastream. That's because the upstream command is reading from the same file that is being written to, overwriting the input with the output.
The solution
rewrite makes it stupid easy to work around this problem. Just pipe the output of your workflow to rewrite f and you'll get the result you expected. Easy peasey!
An example
Say we want to sort a file. We don't want to sort a copy of the file, we want to sort the file itself (obviously). Unfortunately, it's not that easy. Here's an example wherein we select 1024 random words from a dictionary file and then want to sort the output.
shuf -n 1024 /usr/share/dict/words > words.txt
We can easily sort this list with the sort utility, but what happens when we try to save the output to itself?
sort words.txt > words.txt #don't do this!
This will result in a complete loss of data, as sort does not pre-load the entire contents of the file argument in memory before sorting and writing the output (thank god, or else you'd never be able to sort anything larger than a few MB without thrashing your system memory). So we end up doing something like this:
sort words.txt > temp
mv temp words.txt
Which is easy & straightforward enough, except when sort is part of a bigger workflow or a script, or when you forget, or when you don't have as straightforward of a case and don't realize that your source and destination files are one and the same. rewrite to the rescue!
Here's how simple using rewrite here would be:
sort words.txt | rewrite words.txt
Internally, rewrite does all the "magic" of reading from stdin and buffering the content until the upstream command has finished executing, then writing the output to the named file accordingly.
rewriterewrite is written in rust for performance, safety, and out-of-the-box cross-platform support. Installing rewrite (presuming it's not already available as a binary for your platform in your favorite package manager) is as simple as
cargo install rewrite
Pre-built binaries for Windows and OS X are available separately.