[pp:exec] support more replacement fields for '--exec' (#4633)

- {_directory}
- {_filename}
- {_path} (alias for {})

gallery_dl/option.py

@@ -510,6 +510,8 @@ def build_parser():
         dest="postprocessors", metavar="CMD",
         action=AppendCommandAction, const={"name": "exec"},
         help=("Execute CMD for each downloaded file. "
+              "Supported replacement fields are "
+              "{} or {_path}, {_directory}, {_filename}. "
               "Example: --exec \"convert {} {}.png && rm {}\""),
     )
     postprocessor.add_argument(
@@ -518,7 +520,8 @@ def build_parser():
         action=AppendCommandAction, const={
             "name": "exec", "event": "finalize"},
         help=("Execute CMD after all files were downloaded successfully. "
-              "Example: --exec-after \"cd {} && convert * ../doc.pdf\""),
+              "Example: --exec-after \"cd {_directory} "
+              "&& convert * ../doc.pdf\""),
     )
     postprocessor.add_argument(
         "-P", "--postprocessor",

gallery_dl/postprocessor/exec.py

@@ -12,6 +12,7 @@ from .common import PostProcessor
 from .. import util, formatter
 import subprocess
 import os
+import re
 
 
 if util.WINDOWS:
@@ -32,6 +33,7 @@ class ExecPP(PostProcessor):
         args = options["command"]
         if isinstance(args, str):
             self.args = args
+            self._sub = re.compile(r"\{(_directory|_filename|_path|)\}").sub
             execute = self.exec_string
         else:
             self.args = [formatter.parse(arg) for arg in args]
@@ -69,11 +71,8 @@ class ExecPP(PostProcessor):
         if archive and archive.check(pathfmt.kwdict):
             return
 
-        if pathfmt.realpath:
-            args = self.args.replace("{}", quote(pathfmt.realpath))
-        else:
-            args = self.args.replace("{}", quote(pathfmt.realdirectory))
-
+        self.pathfmt = pathfmt
+        args = self._sub(self._replace, self.args)
         self._exec(args, True)
 
         if archive:
@@ -90,5 +89,13 @@ class ExecPP(PostProcessor):
         self.log.debug("Running '%s'", args)
         subprocess.Popen(args, shell=shell)
 
+    def _replace(self, match):
+        name = match.group(1)
+        if name == "_directory":
+            return quote(self.pathfmt.realdirectory)
+        if name == "_filename":
+            return quote(self.pathfmt.filename)
+        return quote(self.pathfmt.realpath)
+
 
 __postprocessor__ = ExecPP