Bash-如何区分控制运算符和元字符？

Question

According to bash manual :

control operator

A token that performs a control function. It is a newline or one of the following: '||', '&&', '&', ';', ';;', '|', '|&', '(', or ')'.

metacharacter

A character that, when unquoted, separates words. A metacharacter is a blank or one of the following characters: '|', '&', ';', '(', ')', '<', or '>'.

Many characters are both control operator and metacharacter .

So how could I konw the syntax category of eg a ; ?

Take if COND ; then CMD ; fi if COND ; then CMD ; fi if COND ; then CMD ; fi as an example.

; seems like a control operator in the context, for it can be substituted by newline . However removing pre and post space s around ; still works ok. Isn't it supposed to be separated by sapces if it's an operator ?

Answer 1

According to the bash manual, an operator is:

A control operator or a redirection operator . See Redirections, for a list of redirection operators. Operators contain at least one unquoted metacharacter.

The metacharacter is basically any character that cannot be part of a word.

Definition of word :

A sequence of characters treated as a unit by the shell. Words may not include unquoted metacharacters.

There is no need for spaces around operators because they always contain metacharacters , which makes the parser know it is not part of the word .

An exception is redirection , where eg

ls 2>&1

requires a space prior to the redirection statement since the operator has a parameter 2 , and requires the parameter to be next to the operator (otherwise it will be a parameter to ls ).