Syntax

This section covers shell syntax: how commands are parsed, how values are expanded, and how special characters are interpreted.

Topics

• Quoting - Single quotes, double quotes, escaping
• Redirection - Input/output redirection, here-documents
• Pipes - Pipelines and command chaining
• Expansion - Parameter, command, arithmetic, brace, tilde, glob
• Heredocs - Here-documents and here-strings

Expansion Order

Shell expansion happens in this order (per POSIX):

1. Brace expansion - {a,b,c}, {1..10}
2. Tilde expansion - ~, ~/path
3. Parameter expansion - $var, ${var:-default}
4. Command substitution - $(cmd)
5. Arithmetic expansion - $((expr))
6. Field splitting - Using IFS
7. Pathname expansion (globbing) - *, ?, [...]
8. Quote removal - Remove quotes after expansion

Source: src/scripting/expansion.f90

Command Structure

A simple command consists of:

[VAR=value...] command [arguments...] [redirections...]

Commands can be combined:

Grouping

# Subshell (separate environment)
(cmd1; cmd2)

# Command group (same environment)
{ cmd1; cmd2; }

Note: Brace groups require the final semicolon and spaces around braces.