Implement lowercase and uppercase, e.g. ${prev,,}

Used by bash_completion.

core/libstr.py

@@ -182,6 +182,18 @@ def DoUnarySuffixOp(s, op, arg):
       else:
         return s
 
+    elif op.op_id == Id.VOp1_Comma:  # Only lowercase the first letter
+      return s[0].lower() + s[1:]
+
+    elif op.op_id == Id.VOp1_DComma:
+      return s.lower()
+
+    elif op.op_id == Id.VOp1_Caret:  # Only uppercase the first letter
+      return s[0].upper() + s[1:]
+
+    elif op.op_id == Id.VOp1_DCaret:
+      return s.upper()
+
     else:  # e.g. ^ ^^ , ,,
       raise AssertionError(op.op_id)
 

doc/architecture-notes.md

@@ -70,6 +70,11 @@ This isn't re-parsing, but it's re-reading.
 - ${s:1:2} -- offsets in code points
 - ${x#?} and family (not yet implemented)
 
+Where bash respects it:
+
+- [[ a < b ]] and [ a '<' b ] for sorting
+- ${foo,} and ${foo^} for lowercase / uppercase
+
 ## Parse-time and Runtime Pairs
 
 - echo -e '\x00\n' and echo $'\x00\n' (shared in OSH)

spec/var-op-other.test.sh

@@ -440,3 +440,29 @@ echo -${s:1:3}-
 ## N-I dash stdout-json: ""
 ## N-I bash status: 0
 ## N-I bash stdout-json: "slice\n-bcd-\n"
+
+#### Lower Case with , and ,,
+x='ABC DEF'
+echo ${x,}
+echo ${x,,}
+## STDOUT:
+aBC DEF
+abc def
+## END
+## N-I dash/mksh/zsh stdout-json: ""
+## N-I dash status: 2
+## N-I mksh/zsh status: 1
+
+
+#### Upper Case with ^ and ^^
+x='abc def'
+echo ${x^}
+echo ${x^^}
+## STDOUT:
+Abc def
+ABC DEF
+## END
+## N-I dash/mksh/zsh stdout-json: ""
+## N-I dash status: 2
+## N-I mksh/zsh status: 1
+