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Each line of input to ae (hereafter, the shell) is first broken into words which are then collected to form commands. A word is either a special word which is one of
> >> >& < << <& <<- <> & && | || ; ;; ( )
or a normal word which is any string of characters terminated by an unquoted special word or unquoted white space (space, tab, newline). See Quoting below.
The special words in the first row are used for input/output redirection and if any is preceded immediately by one or two digits, it includes that digit in the word. The words in the second row, along with the newline character, serve to terminate commands and affect how they are executed.
A number of normal words take on a special meaning if they appear at the beginning of a command. These are reserved words and are
if ifnot else elif elifnot fi for in while until
do done case esac { }
These serve to build the Structured Commands described below.
The final type of word is an assignment word which is a special type of normal word and has, as a prefix, a valid variable name (See Parameters and Variables below) and an equals sign `=', all unquoted. Such a word is interpreted specially only if it is early in a command, preceded only by I/O redirection or other assignment words or if the `k' flag is in effect.
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