Add more expansion features

Closes: #47

expandvars.py

@@ -196,6 +196,10 @@ def expand_modifier_var(vars_, nounset, environ, var_symbol):
     if vars_[0] == "!":
         indirect = True
         vars_ = vars_[1:]
+    elif vars_[0] == "#":
+        return expand_length(
+            vars_[1:], nounset=nounset, environ=environ, var_symbol=var_symbol
+        )
     else:
         indirect = False
 
@@ -264,7 +268,7 @@ def expand_advanced(var, vars_, nounset, indirect, environ, var_symbol):
             var, vars_[1:], nounset=nounset, environ=environ, var_symbol=var_symbol
         )
 
-    return expand_offset(
+    return expand_with_offset(
         var, vars_, nounset=nounset, environ=environ, var_symbol=var_symbol
     )
 
@@ -292,7 +296,7 @@ def expand_strict(var, vars_, nounset, environ, var_symbol):
     raise MissingClosingBrace("".join(buff))
 
 
-def expand_offset(var, vars_, nounset, environ, var_symbol):
+def expand_with_offset(var, vars_, nounset, environ, var_symbol):
     """Expand variable with offset."""
 
     buff = []
@@ -306,7 +310,7 @@ def expand_offset(var, vars_, nounset, environ, var_symbol):
                 raise OperandExpected(var, offset_str)
             else:
                 offset = int(offset_str)
-            return expand_length(
+            return expand_with_len(
                 var,
                 vars_[n:],
                 offset,
@@ -333,7 +337,7 @@ def expand_offset(var, vars_, nounset, environ, var_symbol):
     raise MissingClosingBrace("".join(buff))
 
 
-def expand_length(var, vars_, offset, nounset, environ, var_symbol):
+def expand_with_len(var, vars_, offset, nounset, environ, var_symbol):
     """Expand variable with offset and length."""
 
     buff = []
@@ -409,6 +413,35 @@ def expand_default(var, vars_, set_, nounset, indirect, environ, var_symbol):
     raise MissingClosingBrace("".join(default))
 
 
+def expand_length(vars_, nounset=False, environ=os.environ, var_symbol="$"):
+    """Expand length of a variable."""
+
+    buff = []
+    for c in vars_:
+        if c == "}":
+            n = len(buff) + 1
+            var = "".join(buff)
+            val = getenv(
+                var, nounset=nounset, indirect=False, environ=environ, default=""
+            )
+            if val:
+                return str(len(val)) + expand(
+                    vars_[n:], nounset=nounset, environ=environ, var_symbol=var_symbol
+                )
+            if RECOVER_NULL is not None:
+                return str(len(RECOVER_NULL)) + expand(
+                    vars_[n:], nounset=nounset, environ=environ, var_symbol=var_symbol
+                )
+            raise ParameterNullOrNotSet(var, None)
+
+        if _valid_char(c):
+            buff.append(c)
+        else:
+            raise BadSubstitution(vars_)
+
+    raise MissingClosingBrace("".join(buff))
+
+
 def expand(vars_, nounset=False, environ=os.environ, var_symbol="$"):
     """Expand variables Unix style.
 

tests/test_expandvars.py

@@ -130,6 +130,33 @@ def test_offset_length():
     assert expandvars.expandvars("${FOO:-3:1}:bar") == "damnbigfoobar:bar"
 
 
+@patch.dict(env, {"THREE": "abc", "FOUR": "abcd", "SIX": "abcdef"})
+def test_length():
+    importlib.reload(expandvars)
+
+    assert expandvars.expandvars("${#THREE}") == "3"
+    assert expandvars.expandvars("${#THREE}${#FOUR}") == "34"
+    assert expandvars.expandvars("foo${#SIX}$SIX") == "foo6abcdef"
+
+
+@patch.dict(env, {"FOO": "abcabbcd", "BAR": "xabcabbcd", "ABC": "abc"})
+def test_pattern_substitution_startswith():
+    importlib.reload(expandvars)
+
+    assert expandvars.expandvars("${FOO#abc}") == "abbcd"
+    assert expandvars.expandvars("${FOO#a*c}") == "abbcd"
+    assert expandvars.expandvars("${FOO##a*c}") == "d"
+    assert expandvars.expandvars("${FOO#a?c}") == "abbcd"
+    assert expandvars.expandvars("${FOO##a?c}") == "abbcd"
+
+    assert expandvars.expandvars("${FOO#$ABC}") == "abbcd"
+    assert expandvars.expandvars("${FOO#${ABC}}") == "abbcd"
+
+    assert expandvars.expandvars("${BAR#abc}") == "xabcabbcd"
+    assert expandvars.expandvars("${BAR#a*c}") == "xabcabbcd"
+    assert expandvars.expandvars("${BAR##a*c}") == "xabcabbcd"
+
+
 @patch.dict(env, {"FOO": "X", "X": "foo"})
 def test_expandvars_indirection():
     importlib.reload(expandvars)