What is the idiomatic way to write Boolean-style functions in Bash?

You can simplify the workflow by letting the check command provide the status and only explicitly return a failure status when creation fails: `docker_network_exists() { docker network inspect "$1" >/dev/null 2>&1; }` followed by `if docker_network_exists "$network_name"; then log_warn "network already exists"; else docker network create "$network_name" || { log_error "network creation failed"; return 1; }; fi`. Successful functions often need no explicit `return 0`, because they inherit the status of their final successful command. Also, use a name like `docker_network_exists` so the function reads naturally as a predicate.

Bash uses command exit statuses as Boolean values: status 0 means success/true, while any nonzero status means false or failure. So a predicate should return 0 when its condition is true. For example, `docker_network_exists() { docker network inspect "$1" >/dev/null 2>&1; }` can be used directly with `if docker_network_exists "$name"; then ... fi`. A nonzero status does not necessarily mean something went wrong; it can simply mean the condition was false.

The important convention is that zero means success, not that zero universally means a conceptual true value. Shell conditionals check whether a command succeeded, so `if` treats exit status 0 as true. Use `return 1` or another nonzero value when a predicate is false, and reserve explicit error handling for operations such as a failed `docker network create`. For style, choose either `name()` or the `function name` form rather than combining both, and run the script through ShellCheck.