Bash Glossary

Canonical terms for shell that survives production: what an unquoted expansion actually does, and the failure modes that follow from it.

Terms

Associative array:
A bash-only array indexed by arbitrary string keys instead of sequential positions, declared with declare -A before assignment.
Avoid: hash, dictionary, map (say "associative array", the shell's own term, even though the concept is the same one those words name elsewhere)

Background job:
A command started with a trailing &, running without blocking the script that started it; its PID is available in $! immediately afterward.
Avoid: async task, thread (neither applies; a background job is a separate process, not a lighter-weight unit inside one)

Command substitution:
Running a command and replacing $(command) with what it wrote to standard output, trailing newlines stripped.
Avoid: backtick substitution (use for the older, non-nesting ` ` syntax specifically, not the concept)

File descriptor:
A number identifying an open input or output stream for a process; 0, 1, and 2 are standard input, output, and error, and a script may open others.
Avoid: file handle (a term from other languages; this workspace says "file descriptor", matching the shell's own numbering)

Here-doc:
A <<DELIMITER ... DELIMITER block that feeds its contents to a command's standard input inline, without a separate file.
Avoid: heredoc (one word; use the hyphenated form for consistency across lessons)

Indexed array:
A bash-only array whose elements sit at sequential integer positions starting at 0, created with arr=(a b c).
Avoid: list, plain array (say "indexed array" once associative arrays are also in scope, so the two aren't confused)

Local variable:
A variable declared with local inside a function, scoped to that function call rather than persisting in the calling shell's environment.
Avoid: function-scoped variable (say "local variable", matching the keyword)

Parameter expansion:
A ${...} form that defaults, validates, transforms, or measures a variable's value inline, rather than merely reading it back.
Avoid: variable substitution (reserve "substitution" for command substitution specifically, to keep the two distinct)

Pathname expansion (globbing):
Replacing a word containing *, ?, or [ with the filenames that match it, applied to unquoted expansions before the shell treats the result as arguments.
Avoid: glob expansion (use "globbing" or the full term)

Process substitution:
A bash-only <(command) or >(command) form that lets a command's output or input be treated as a readable or writable file, without a pipe or a temporary file.
Avoid: process piping (this is not a pipe; the whole point is that it avoids a pipeline's subshell)

Signal:
An asynchronous notification sent to a process (SIGTERM, SIGINT, SIGKILL, and others), caught with trap unless it's SIGKILL, which cannot be handled at all.
Avoid: interrupt (reserve for SIGINT specifically, which is what Ctrl-C sends; "signal" is the general term)

Subshell:
A copy of the current shell's environment, forked to run a command or block; an assignment or a cd made inside it never affects the shell that forked it.
Avoid: child process (true but imprecise here; "subshell" specifically names a forked copy of the shell itself, not any child process)

Symlink attack:
Pre-creating a symlink at a predictable path a script is about to write to, so the script's write follows the link to a file the attacker chose instead.
Avoid: TOCTOU race (a broader, more general term for the same shape of bug; say "symlink attack" for this specific instance of it)

Word splitting:
Breaking an unquoted expansion's result into separate words wherever a character in $IFS (space, tab, newline by default) appears.
Avoid: tokenizing (a different, unrelated meaning in other contexts)