Thus if the alias for `ls' were `ls -l' the command `ls /usr' would become `ls -l /usr', the argument list here being undisturbed. If the alias for `lookup' were `grep !^ /etc/passwd' then `lookup bill' would become `grep bill /etc/passwd'. Aliases can be used to introduce parser metasyntax. For example, `alias print 'pr \!* | lpr'' defines a ``command'' (`print') which pr(1)s its arguments to the line printer.
Alias substitution is repeated until the first word of the command has no alias. If an alias substitution does not change the first word (as in the previous example) it is flagged to prevent a loop. Other loops are detected and cause an error.
Some aliases are referred to by the shell; see Special aliases.
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