Built-in commands

Run help inside nshell for per-command detail, and type NAME to check whether a name resolves to a builtin, a function, or an external program.

agent, ai, alias, abbr, and, bg, bind, break, builtin, cd, command, complete, contains, continue, count, dirs, disown, echo, eval, exec, exit, export, false, fg, function, functions, help, history, jobs, kill, math, nextd, not, or, pipeline-graph, popd, prevd, printf, prompt, pushd, pwd, read, seq, set, source, string, test, theme, true, type, unset, wait, which.

Notes on a few of them

abbr registers an abbreviation that expands inline as you type, so history records the expanded command. Prefer it to alias when you want the short form only while typing.

ai controls the assistant session. ai status shows sidecar state and usage, ai reset clears the conversation, ai log [N] shows recent audit entries, and ai set KEY VALUE changes effort, model, max-steps, or budget.

agent starts an interactive assistant task. It requires a terminal, and proposed commands require confirmation before execution.

pipeline-graph renders a typed pipeline as a Graphviz DOT graph, or a Mermaid flowchart with --mermaid, without executing it. Quote the pipeline so the shell passes it as one argument — see Recipes.

bind lists, sets, erases, or resets key bindings: bind alone lists every binding, bind KEY shows one, bind KEY ACTION rebinds a key, bind -e KEY erases a binding (the key then does nothing), and bind --reset restores every default. See Customizing key bindings.

theme picks or tunes the color theme: theme list shows the presets, theme use NAME switches to one, theme set ROLE SPEC overrides a single role, and theme show prints the active theme. See Customizing colors.

prompt picks the prompt's layout: prompt show prints the active left and right format strings, prompt left FORMAT/prompt right FORMAT install one, prompt preview FORMAT renders a format without installing it, and prompt reset restores the defaults. See Customizing the prompt.

string is the fish-style string toolkit (string upper, string split, and friends) rather than a single-purpose command. Every subcommand rejects an option it does not define instead of silently treating it as data; -- ends option parsing and a lone - is a literal argument. string split supports -m/--max N (split at most N times, leaving the remainder in the last field) and -r/--right (split from the right); string trim supports -l/--left, -r/--right, and -c/--chars CHARS. string match -r and string replace -r report that this build has no regex engine rather than falling back to a literal match.

complete registers completion metadata for a command, feeding the same knowledge base the built-in command catalog uses. complete -C LINE is the scriptable entry point: it prints the completions for LINE, one per line, without registering anything.

and / or run their command based on $status, the previous command's exit code: and only if it was 0, or only if it was nonzero. Otherwise they leave $status unchanged. not (see above) already exists for inverting a status; and/or chain on it the way &&/|| chain commands within one line.

math is fish's calculator: math '1 + 2 * 3', parentheses, unary minus, and decimals. Division renders as a decimal (math '10 / 4' is 2.5), trimmed to at most 6 fraction digits. Division by zero exits 1; a malformed expression exits 2.

dirs, pushd, popd manage a directory stack: pushd DIR remembers the current directory and switches to DIR; popd returns to the most recently remembered one; dirs lists the stack, current directory first, ~-shortened. pushd with no argument swaps the current directory with the top of the stack. prevd / nextd walk a separate, append-only history of every directory visited via cd, pushd, or popd.

functions lists defined function names (one per line); functions NAME prints its reconstructed definition, noting the source file when the function came from one; functions -e NAME erases it. builtin NAME runs a builtin directly, bypassing any function or alias of the same name.

set manages shell variables: bare set lists everything currently visible, set -x NAME VALUE... exports, set -e NAME erases, and set -q NAME tests whether a name is defined. -l/--local and -g/--global pick the scope explicitly and combine with -x (-lx, -gx); with neither flag, set updates a name already visible in an enclosing scope in place and otherwise creates a new local one. Every function call gets its own local scope, popped when the call returns, so a local variable set inside one disappears at the end of that call. -U/--universal is rejected (exit 2); nshell has no universal-variable store.

disown removes a job from the shell's job table so it survives exit, complementing jobs, fg, and bg. With no argument it acts on the current job, the same convention fg and bg use.

test (and [) supports file tests (-e -f -d), string tests (-n -z = !=), and numeric comparisons (-eq -ne -lt -le -gt -ge). An unrecognized operator or a non-integer operand to a numeric comparison is a diagnosed usage error (exit 2), distinct from a false result (exit 1).