TODO env sub

env_sub.py

@@ -0,0 +1,117 @@
+import argparse
+import os
+import re
+import sys
+
+
+def create_options():
+    parser = argparse.ArgumentParser(
+        description="Rewrites input to output expanding environment variables"
+    )
+    parser.add_argument(
+        "-g",
+        "--greedy-defaults",
+        action="store_true",
+        help="allow expansion of undefined variable defaults",
+    )
+    parser.add_argument(
+        "-v",
+        "--variable",
+        action="append",
+        help="restrict expansion to named variables only",
+        metavar="VAR",
+    )
+    parser.add_argument(
+        "-p",
+        "--prefix",
+        default="${",
+        help="set the expansion prefix marker (default: ${)",
+        metavar="PREFIX",
+    )
+    parser.add_argument(
+        "-s",
+        "--suffix",
+        default="}",
+        help="set the expansion suffix marker (default: })",
+        metavar="SUFFIX",
+    )
+    parser.add_argument(
+        "-V",
+        "--version",
+        action="version",
+        version="1.0",
+        help="print the version and exit",
+    )
+    return parser
+
+
+def print_usage(program):
+    print(f"Usage: {program} [options]")
+    print()
+    print("Rewrites input to output expanding environment variables")
+    print()
+    print("NOTE: Only ${ENV_VAR} and ${ENV_VAR-default value} are supported")
+    print("      (and you are on your own if your default value needs to include")
+    print("      a } character)")
+    print()
+
+
+def main():
+    parser = create_options()
+    args = parser.parse_args()
+
+    prefix = args.prefix
+    suffix = args.suffix
+    greedy = (
+        re.compile(
+            rf"{re.escape(prefix)}[a-zA-Z_][a-zA-Z0-9_]*:?-(.*?)" + re.escape(suffix)
+        )
+        if args.greedy_defaults
+        else None
+    )
+
+    if args.variable:
+        vars = {}
+        for var_name in args.variable:
+            vars[var_name] = (
+                re.compile(
+                    rf"{re.escape(prefix)}{var_name}((:?-)(.*?))??" + re.escape(suffix)
+                ),
+                os.getenv(var_name),
+            )
+    else:
+        vars = {
+            key: (
+                re.compile(
+                    rf"{re.escape(prefix)}{key}((:?-)(.*?))??" + re.escape(suffix)
+                ),
+                os.getenv(key),
+            )
+            for key in os.environ
+        }
+
+    for line in sys.stdin:
+        out = line.strip()
+        for var_name, (regex, value) in vars.items():
+            out = regex.sub(lambda match: handle_match(match, value), out)
+
+        if greedy:
+            out = greedy.sub(lambda match: match.group(1) or "", out)
+
+        sys.stdout.write(out + "\n")
+        sys.stdout.flush()
+
+
+def handle_match(caps, val):
+    if caps.group(2):
+        if caps.group(2) == ":-":
+            return val if val and val.strip() else caps.group(3) or ""
+        else:
+            return val or caps.group(3) or ""
+    else:
+        return val or caps.group(0)
+
+
+if __name__ == "__main__":
+    main()
+    main()