lists.md

Shell behaviors and data

"Things" that can be evaluated/manipulated by a shell:

• strings (literals, other...)
• variables
• arithmetic
• builtins
• subshells
• forked processes (non-shell)
• File contents (reading)
• File contents (writing/appending)
• Temp files (reading, writing...)
• Shell builtins/operators/etc via 'eval'

...These can be evaluated as...

• nothing (e.g. no output captured from a subshell)
• strings
• ints
• floats (...not in most shells!)
• arrays of strings
• assoc-arrays of strings (fairly recent in Bash)
• string-streams (e.g. w/ pipes & redirection)
• file-handles
• interpretable shell code
• in Nu/PowerShell/etc: structured data of some kind

Strings/code have multiple levels of "expansion." In Bash, in order:

1. Brace expansion
2. Tilde expansion
3. Together:
   • Parameter expansion
   • Arithmetic expansion
   • Command substitution
4. Word splitting
5. Pathname expansion