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############################################################################
#
# File: varsub.icn
#
# Subject: Procedure to perform UNIX-shell-style substitution
#
# Author: Robert J. Alexander
#
# Date: November 2, 1995
#
############################################################################
#
# This file is in the public domain.
#
############################################################################
#
# Variable values are obtained from the supplied procedure, "varProc",
# which returns the value of its variable-name argument or fails if
# there is no such variable. "varProc" defaults to the procedure,
# "getenv".
#
# As with the UNIX Bourne shell and C shell, variable names are
# preceded by $. Optionally, the variable name can additionally be
# surrounded by curly braces {}, which is usually done when necessary
# to isolate the variable name from surrounding text.
#
# As with the C-shell, the special symbol ~<username> is handled.
# Username can be omitted, in which case the value of the variable
# "HOME" is substituted. If username is supplied, the /etc/passwd file
# is searched to supply the home directory of username (this action is
# obviously not portable to non-UNIX environments).
#
############################################################################
procedure varsub(s,varProc)
local var,p,user,pw,i,c,line
static nameChar
initial nameChar := &letters ++ &digits ++ "_"
/varProc := getenv
s ? {
s := ""
while s ||:= tab(upto('$~')) do {
p := &pos
s ||:= case move(1) of {
"$": {
if c := tab(any('{(')) then var := tab(find(map(c,"{(","})"))) &
move(1)
else var := tab(many(nameChar)) | ""
"" ~== varProc(\var) | &subject[p:&pos]
}
"~": {
if user := tab(many(nameChar)) || ":" then {
if pw := open("/etc/passwd") then {
(while line := read(pw) do
if match(user,line) then break) | (line := &null)
close(pw)
if \line then {
every i := find(":",line)\5
i +:= 1
line[i:find(":",line,i)]
}
else &subject[p:&pos]
}
else &subject[p:&pos]
}
else getenv("HOME")
}
}
}
s ||:= tab(0)
}
return s
end
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