#tee #subcommand #parser #unix-style

app iomux

Multiplex stdout, stderr, and other info about child commands

1 unstable release

0.1.0 May 12, 2023

MIT license

620 lines

The iomux binary multiplexes the stdout, stderr, and other info about a set of child process into stdout.

The design is unix-like, aiming to provide output that's convenient for unix tools (grep, sed, etc…).

Example - Aggregate stdout/stderr in a parseable format

Sometimes it's useful to aggregate stdout/stderr and then later parse them out.

$ iomux find /etc/ | tee find.log
12971> spawned "find" "/etc/"
12971  /etc/
12971  /etc/ssl/private
12971! find: ‘/etc/ssl/private’: Permission denied
12981  /etc/passwd
12981  /etc/timezone
12981> exit 1

The output above is all on stdout including both the stdout and stderr of find as well as metadata about the find process, such as its arguments and exit status.

Each line begins with the PID of find, then a "tag" indicating the source of information for that line:

  • > metadata about the find process.
  • stdout
  • ! stderr

Parsing find.log

We can parse the log using standard unix tools to answer various queries We can reproduce the stderr stream with standard unix text manipulation:

Determining the PID of find

$ grep '^[0-9]*>' find.log | head -1 | sed 's/>.*$//'

Reproducing stdout

$ grep '^[0-9]* ' ./find.log | sed 's/^[0-9]*  //'

Reproducing stderr

$ grep '^[0-9]*!' ./find.log | sed 's/^[0-9]*! //'
find: ‘/etc/ssl/private’: Permission denied

Determining the exit status

$ grep '^[0-9]*> exit' ./find.log | sed 's/^.*exit //'

Example - Log environmental details of a build

Suppose you are automating a build process which uses make and want to log the approximate launch timestamp, environment, pwd, etc… Using iomux you could aggregate this info like so:

$ iomux -- date --iso=s -- pwd -- env -- make | tee build.log

The output in build.log interleaves the info from those child processes in a line-oriented format that makes unix-style text processing convenient.

Example - Merge logs

I like to see both my system journal and my desktop log in one place:

$ iomux -- journalctl -f -- tail -F ~/.xsession-errors


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