Bash 라인 설명 프로세스

bash가 행 해석을 수행하는 정확한 프로세스를 이해하고 싶습니다.

GNU bash 참조 매뉴얼에서:

When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to right.

1. The words that the parser has marked as variable assignments (those preceding the command name) and redirections are saved for later processing.

2. The words that are not variable assignments or redirections are expanded (see Shell Expansions). If any words remain after expansion, the first word is taken to be the name of the command and the remaining words are the arguments.

3. Redirections are performed as described above (see Redirections).

4. The text after the ‘=’ in each variable assignment undergoes tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal before being assigned to the variable.

If no command name results, the variable assignments affect the current shell environment. Otherwise, the variables are added to the environment of the executed command and do not affect the current shell environment. If any of the assignments attempts to assign a value to a readonly variable, an error occurs, and the command exits with a non-zero status.

If no command name results, redirections are performed, but do not affect the current shell environment. A redirection error causes the command to exit with a non-zero status.

If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of the expansions contained a command substitution, the exit status of the command is the exit status of the last command substitution performed. If there were no command substitutions, the command exits with a status of zero.

이제 간단한 예를 들어보겠습니다.

var="hello friend"

echo ${var}s > log.txt

지금 무슨 일이 일어나는거야?

참조에 따르면 var 할당(1)은 확장(4) 후에 발생하지만 쉘은 변수 할당을 먼저 수행하지 않고 어떻게 var를 확장합니까?

이것이 제가 여기서 놓친 부분인지 아니면 단지 매뉴얼에 대한 오해인지는 모르겠습니다.

좀 더 이해를 돕기 위해 더 많은 예를 들어주시면 감사하겠습니다.

감사해요