duality is a Go program that allows you to run multiple commands in parallel and see their output interleaved in real-time.

When duality starts, each command gets a unique ID and its output is prefixed with that ID plus whether the output was rendered to stdout or stderr in the format [ID][stdout|stderr] log message.

Each command is run in parallel and their output is interleaved in real-time. If a command exits, duality will print the exit status and the command's ID. If the exit code is non-zero, duality will exit with a non-zero exit code.

If any of the command fails, all other commands are sent a SIGTERM signal, but duality won't wait for them to be closed, then duality will exit with a non-zero exit code.

If duality receives a SIGINT or SIGTERM signal, it will forward a SIGTERM signal to all commands and exit with a non-zero exit code. Killing duailty will also kill all commands.

By default, all commands are run through a shell, using /bin/bash -c as a default. This will allow you to do some more advanced commands, like sleep 10 && echo "Hello". You can change the shell used by setting the DUALITY_SHELL_COMMAND environment variable (e.g. export DUALITY_SHELL_COMMAND="/bin/ash -c").

You can download the latest release from the releases page.

Simply run the command with arguments, where each argument is a single command. If you want to ensure the commands are processed appropriately, ensure they're quoted properly.

$ duality "echo Hello" "echo World"
[75ra32uh] running: /bin/bash -c "echo World"
[52updl62] running: /bin/bash -c "echo Hello"
[52updl62][stdout] Hello
[52updl62] "echo Hello" executed successfully (exit code: 0)
[75ra32uh][stdout] World
[75ra32uh] "echo World" executed successfully (exit code: 0)

The log output will tell you what command and what shell interpreter will be used to run the command. Any log statements sent to stdout or stderr will be prefixed with the command ID and whether it was sent to stdout or stderr. When a command finishes, duality will print the exit status and the command ID. On any failed command, duality will exit with a non-zero exit code and report the error back to you, without prefixes.

At least one command must be provided, otherwise duality will exit with a non-zero exit code. Providing empty commands in between non-empty commands is allowed, but the empty commands will be skipped.

In Docker, we provide a convenience image that you can use to run duality in a container:

ghcr.io/patrickdappollonio/duality:v1

Note this image is based on busybox, and as such, the shell used is sh. The binary is located at /usr/local/bin/duality.

If you need a different shell, you can also use the image ghcr.io/patrickdappollonio/duality as a build step to easily download the binary, then copy it to your own image, effectively allowing you to change to any shell you want. Here's an example:

FROM ghcr.io/patrickdappollonio/duality:v1 as duality

FROM bash:latest
COPY --from=duality /usr/local/bin/duality /usr/local/bin/duality

By having it in your own image, you set the rules: you can use any shell (just make sure you tell duality which shell to use by setting the DUALITY_SHELL_COMMAND environment variable) and you can change entrypoints and other settings as you see fit.

The IDs are generated based on the command being executed and its position as provided to the duality program. In practice, a command will always yield the same ID as long as:

• The string representation of the command hasn't changed
• The position of the command, as provided to the CLI, hasn't changed

This process makes IDs predictable and easy to grep.

If you want to maintain a position after deleting a command, you can pass an empty string as a parameter. This will ensure the ID is kept, but the empty command will be skipped:

$ duality "foo" "bar" "baz"
[9zmorkes] running: /bin/bash -c "baz"
[qex9920b] running: /bin/bash -c "foo"
[2mlvq8wb] running: /bin/bash -c "bar"

$ duality "foo" "" "baz"
[9zmorkes] running: /bin/bash -c "baz"
[qex9920b] running: /bin/bash -c "foo"

Note in the example above, the IDs qex9920b and 9zmorkes were maintained, even when now the second command is empty.