Substitutions are used to abbreviate user names or addresses by inserting a character string into the rewritten address, the value of which is determined by the particular substitution sequence used. For example, in the template:
the $U is a substitution sequence. It causes the username portion of the address being rewritten to be substituted into the output of the template. Thus, if jdoe@mailhost.acme.com was being rewritten by this template, the resulting output would be jdoe@acme.com, the $U substituting in the username portion, jdoe, of the original address.
Substitution Sequence
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Substitutes
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$D
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Portion of domain specification that matched
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$H
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Unmatched portion of host/domain specification; left of dot in pattern
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$L
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Unmatched portion of domain literal; right of dot in pattern literal
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$U
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Username from original address
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$$
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Inserts a literal dollar sign ($)
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$%
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Inserts a literal percent sign (%)
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$@
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Inserts a literal at sign (@)
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$\
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Force material to lowercase
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$^
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Force material to uppercase
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$_
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Use original case
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$W
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Substitutes in a random, unique string
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$[...]
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Invoke customer-supplied routine; substitute in result
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$(text)
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General database substitution; rule fails if lookup fails
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${...}
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Apply specified mapping to supplied string
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$&n
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nth part of unmatched (or wild card) host, as counting from left to right, starting from 0
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$!n
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nth part of unmatched (wild card) host, as counted from right to left, starting from 0
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$*n
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nth part of matching pattern, as counting from left to right, starting from 0
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$#n
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nth part of matching pattern, as counted from right to left, starting from 0
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