When writing code that needs the current time, don’t hardcode a reference to the current time.

When programming, you may have to work with dates and times in different time-zones, or look at events in calendars in the past or future. You can do all of these using GUI tools, but your Unix command-line is there for you (and easier to script).

If you’re introducing Kotlin to an existing Java codebase, you’ll probably have places in your code where new Kotlin code has to call existing Java code, or vice-versa. Kotlin’s default behavior for Java interop poses a subtle, but significant safety problem with nullability.

When working on the command-line, it’s often useful to paste from the system clipboard to a command-line tool, or to copy output from the command-line into your system clipboard.

On macOS, pbcopy and pbpaste do this. On Linux, you can use xclip or xsel.

Bash/Zsh curly-brace expansion is simple but powerful: each permutation enclosed in braces is expanded, recursively, before glob expansion: