S6E2: "Environmental Protection"

Posted 2021-03-14 23:59
Modified 2021-03-14 00:36
Comments 0

We talk about environment variables, how they interact, and how processes use them.

Jthan is the human incarnation of online recipes.

• Just the Tip
• Notes
• 15 Clams
• Errata
• Music

Just the Tip

• Paden talks about pushd and popd.
  • I also tell the guys about cd - (not cd ~!).

Notes

Starts at 26m40s.

I was drinking water. Paden was drinking a Sprite. Jthan was drinking a GIbson.

• Environment variables
  • Jthan briefly mentions the env command (env (1))
  • I talk about how to parse /proc/<PID>/environ files by splitting on the nullbyte. (e.g. s.split('\x00'))
  • A common issue is a missing path from ${PATH} within a cron task. The PATH env var must be specified explicitly in cron jobs! (Also, MAILTO! Info here.)
  • Services can (and frequently do) have different environment variables than what you might expect!
    • The systemd EnvironmentFile does not do shell or command interpolation! So you can’t use something like export FOO="BAR", FOO=${BAZ}, or FOO=$(quux).
  • Take note of sudo -E!
  • Jthan mentions prefixing a command with a space to prevent it from being written to the bash history. I mentioned it doesn’t work for my laptop or desktop. I thought it was because I use a custom HISTTIMEFORMAT but it’s actually because Arch Linux follows upstream defaults, and upstream Bash does not set HISTCONTROL whereas CentOS does! Problem solved.

15 Clams

In this segment, Jthan shares with you a little slice of life. The title is a reference to this video. (2m16s in)

Starts at 54m18s.

Jthan wants to know what the best approach is for someone who sees improvements that can be made at a new job.

Errata

• Jthan and I talk about the G.I. Joe PSA parodies.
• You can find more info on dash here.
  • And yes, it’s “Debian Almquist SHell”.

Music

Author r00t^2
Categories Season Six