Substitute and parseCommand: The now recognise variables and deal with them as needed

src/fsh.nim

@@ -4,11 +4,21 @@
 
 # imports
 import streams
-import strutils
 import osproc
+import strtabs
+import os
+
+# globals
+var shellVariables = newStringTable(modeCaseSensitive)
+# Environment variables get defined in a separate var
+var envVariables = newStringTable(modeCaseSensitive)
+# populate the table
+for k, v in envPairs():
+  envVariables[k]=v
 
 # forward declarations
 proc eval(cmd: string): string
+proc substitute(strm: Stream, delim = ";\p"): string
 
 # skipSpaces reads the stream until a non-space character is found
 proc skipSpaces(strm: Stream): int =
@@ -104,6 +114,34 @@ proc readCommand(strm: Stream): string =
       of '\n', '\r', ';': break
       else: result.add(c)
 
+# readVariable reads a variable
+proc readVariable(strm: Stream): string =
+  let c = strm.readChar()
+  case c:
+    of '{':
+      result = strm.readLiteral()
+    of '[':
+      result.add(strm.readInterpelation)
+    of '"':
+      result.add(strm.readSubstitution())
+    of ']', '}':
+      stderr.write("Unexpected " & c & ".\n")
+    else:
+      result.add(c)
+      while not strm.atEnd():
+        let d = strm.readChar()
+        case d:
+          of 'a'..'z', 'A'..'Z', '0'..'9', '_', ':': result.add(d)
+          else: break
+
+# evalVariable finds a value of a variable
+proc evalVariable(vari: string): string =
+  if shellVariables.hasKey(vari):
+    result=shellVariables[vari]
+  elif envVariables.hasKey(vari):
+    result = envVariables[vari]
+  else: raise newException(Exception, "No such variable: " & vari & ".")
+
 # substitute does a substitution on the stream passed in
 proc substitute(strm: Stream, delim=";\p"): string =
   while not strm.atEnd():
@@ -120,6 +158,7 @@ proc substitute(strm: Stream, delim=";\p"): string =
         stderr.write("Extra closing bracket")
       of '\\':
         result.add(strm.readChar())
+      of '$': result.add(strm.readVariable.evalVariable)
       else:
         result.add(c)
 
@@ -139,6 +178,7 @@ proc parseCommand(cmd: string): seq[string] =
         newitem.add(strm.readInterpelation.eval)
       of '"':
         newitem.add(strm.readSubstitution.newStringStream.substitute)
+      of '$': result.add(strm.readVariable.evalVariable)
       of ' ':
         result.add(newitem)
         newitem = ""