aless

README

# aless

Append lines from stdin to a file, but only if they don't already appear in the file.
Outputs new lines to `stdout` too, making it a bit like a `tee -a` that removes duplicates.

## Usage Example

Here, a file called `things.txt` contains a list of numbers. `newthings.txt` contains a second
list of numbers, some of which appear in `things.txt` and some of which do not. `aless` is used
to append the latter to `things.txt`.


```
▶ cat things.txt
Zero
One
Two

▶ cat newthings.txt
One
Two
Three
Four

▶ cat newthings.txt | aless things.txt
Three
Four

▶ cat things.txt
Zero
One
Two
Three
Four

```

Note that the new lines added to `things.txt` are also sent to `stdout`, this allows for them to
be redirected to another file:

```
▶ cat newthings.txt | aless things.txt > added-lines.txt
▶ cat added-lines.txt
Three
Four
```

## Flags

- To view the output in stdout, but not append to the file, use the dry-run option `-d`.
- To append to the file, but not print anything to stdout, use quiet mode `-q`.

## Install

You can either install using go:

```
go install -v github.com/mk990/aless@latest
```

Or download a [binary release](https://github.com/tomnomnom/aless/releases) for your platform.