# rc shell reference

Quick reference for Plan 9 rc shell syntax. Extracted from plan9port.

## Variables

    var=value            # assignment
    var=(a b c)          # list
    $var                 # expand
    $#var                # count
    $var(2)              # index (1-based)
    $$var                # indirect
    $"var                # stringify list (join with spaces)
    $var^suffix          # concatenate

## Control Flow

    if(test) cmd
    if not cmd

    for(i in list) cmd
    for(i) cmd           # implicit $*

    while(test) cmd

    switch($var) {
    case pattern
        cmd
    case pat1 pat2
        cmd
    }

## Functions

    fn name { body }
    fn sigexit { cleanup }    # trap on exit
    fn sigint { }             # trap ctrl-c

## Pattern Matching

    ~ $var pattern           # true if matches
    ~ $var *.c *.h           # multiple patterns
    ! ~ $var pattern         # negation

## Redirection

    > file                   # stdout
    >> file                  # append
    < file                   # stdin
    >[2] file                # stderr
    >[1=2]                   # merge stdout to stderr
    >[2=1]                   # merge stderr to stdout
    <{cmd}                   # process substitution (in)
    >{cmd}                   # process substitution (out)

## Command Substitution

    `{cmd}                   # split on $ifs
    ``(sep){cmd}             # split on sep

## Process Control

    rfork e                  # new env (copy)
    rfork en                 # new env + namespace
    rfork ns                 # new namespace only

## Status

    $status                  # exit status of last command
    exit ''                  # success
    exit 'error msg'         # failure

## Flags

    flag p && ...            # test if -p flag was passed
    getflags                 # parse flags

## Quoting

    'literal'                # no expansion
    ''                       # empty string
    ''''                     # literal single quote
    # no double quotes -- use ^ for concatenation

## Key Differences from sh/bash

    - No double quotes (use $"var for stringify)
    - path is a list, not colon-separated
    - Lists are first class (not just strings)
    - No export -- env is inherited via fork
    - if/if not instead of if/else/elif
    - ~ for pattern matching instead of [[ ]]
    - fn instead of function
    - $status instead of $?
    - ^ for string concatenation
    - No arithmetic expansion -- use expr or bc