The script command

While doing a testing session this afternoon, Chris mentioned a little command that I hadn’t used before: script allows you to record everything that happens inside a terminal session and to play it back afterwards.

Turns out, it is shipped by default with macOS and most Linux distributions (e.g. as part of the bsdutils package). If all you want to do, is keep a look of commands and their respective output, just run script OUTPUT_FILE. Now, all the commands you enter before closing the terminal session (end with exit or Ctrl-d) will be recorded:

$ script session.typescript
Script started, output file is session.typescript

$ echo "hello"

$ exit
Script done, output file is session.typescript

If you open session.typescript inside an editor you will see not only the commands and their output but also your applied shell prompt! Basically as much as possible of what was visible in the original terminal session.

Sadly, if you want to go beyond the pure logging of commands then the script command on macOS has a different parameter set compared to the one being available for instance on a Debian installation.

Recording a session (for replay)

In order to record a session on macOS that should also be replayable, you would use the following command:

$ script -r session.typescript

On Linux you will actually have to instruct script to generate two files: (1) that holds the commands and their respective output and (2) a timing-file that stores when what should be displayed during replay:

$ script --timing=session.timing session.typescript

Playing back a recording

Since the two commands produce different output files, the replay-functionality also expects different inputs.

On macOS you can reuse the script command but with the -p flag:

$ script -p session.typescript

On Linux replaying is handled by a different command that expects both, the timing file and the typescript:

$ scriptreplay --timing session.timing \
    --typescript session.typescript

Platform-independent recording

If you need to share a replay between platforms, it’s probably worth taking a look at asciinema:

# Record
$ asciinema rec session.cast

# Playback
$ asciinema play session.cast

asciinema stores the recording in a simple JSON format. You can find its specification here.

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