Interactive job control lets a shell manage process groups that share a controlling terminal. The terminal has one foreground process group at a time, while other jobs can run or remain stopped in the background. Foreground ownership, running state, and the shell’s job table are distinct. A background job is not automatically suspended, and a stopped job has not necessarily terminated. ...
An environment is a collection of name-value strings supplied to a program when it starts. A child normally receives the environment selected by its parent; changing that child’s copy does not rewrite the parent’s or a sibling’s copy. This is a useful configuration boundary, but it is not a promise that the command has no side effects. The program can still modify shared files, databases, or other resources using those settings. ...
A wildcard in a Bash command usually becomes a list of pathnames before the target program starts. That makes *.txt convenient, but it also makes the command depend on the current directory and shell options. The program receives arguments, without information saying which ones came from a wildcard. Decide whether you intend to pass matching files or a pattern for the program to interpret. ...
“Command not found” identifies a lookup failure, but lookup does not always mean walking every directory in PATH. In ordinary Bash, a command word without a slash can resolve to a function, builtin, cached executable path, or a newly searched executable. An alias may already have changed the command while the input was read. Inspect the shell that actually reported the failure before reinstalling a tool that may already exist. ...
A wrapper should pass the arguments it received without changing their boundaries. In Bash, "$@" does that when used as command arguments: each positional parameter becomes a separate quoted word. This matters for empty values, spaces, newlines, and literal wildcard characters. A command that happens to work with two simple filenames can still be broken if its wrapper reconstructs the list as a single string. ...
An exit status is a small value that a shell uses to decide what runs next. Zero means success for shell control flow; a nonzero status takes the failure branch. That does not give every number a universal application meaning. A search with no matches, invalid input, and an unavailable server may deserve different handling even though all can produce nonzero results. Read the command’s contract before deciding what to retry or ignore. ...
A shell function groups commands under a name and receives its own positional arguments. In an ordinary call, its body runs in the current shell rather than automatically starting a separate process. That makes functions useful for reusable operations, but it also means assignments, directory changes, and other shell state can affect the caller. A function needs an explicit contract for inputs, output, status, and any intentional side effects. ...
Command substitution captures a command’s standard output and inserts the resulting text into a surrounding expression. The familiar $(command) form is useful for a timestamp, a computed label, or another small textual value. It is not a transparent channel for arbitrary bytes or a reliable way to transport a list of filenames. Its newline handling, execution environment, and exit status are part of the interface you need to understand. ...