update slice help doc

CHANGELOG

@@ -9,7 +9,10 @@ jc changelog
 - Enhance `proc-net-tcp` parser to add opposite endian support for architectures
   like the s390x
 - Enhance `url` parser to add `parent`, `filename`, `stem`, and `extension` fields
+- Enhance `/proc` file magic syntax to allow slurping when multiple files are selected
+  and to include the `_file` metadata field in the data
 - Fix `ini` and `ini-dup` parsers to consistently handle null values as empty strings
+- Fix line slicer to not skip blank lines
 - Add source link to online parser documentation
 - Add snap package build scripts
 - Refactor parser aliases for `kv`, `pkg_index_deb`, `lsb_release`, and `os-release`

jc/cli.py

@@ -21,7 +21,7 @@ from .jc_types import JSONDictType, CustomColorType, ParserInfoType
 from . import utils
 from .cli_data import (
     long_options_map, new_pygments_colors, old_pygments_colors, helptext_preamble_string,
-    helptext_end_string
+    slicetext_string, helptext_end_string
 )
 from .shell_completions import bash_completion, zsh_completion
 from . import tracebackplus
@@ -289,7 +289,7 @@ class JcCli():
         """Return the help text with the list of parsers"""
         parsers_string: str = self.parsers_text()
         options_string: str = self.options_text()
-        helptext_string: str = f'{helptext_preamble_string}{parsers_string}\nOptions:\n{options_string}\n{helptext_end_string}'
+        helptext_string: str = f'{helptext_preamble_string}{parsers_string}\nOptions:\n{options_string}\n{slicetext_string}\n{helptext_end_string}'
         return helptext_string
 
     def help_doc(self) -> None:

jc/cli_data.py

@@ -79,6 +79,17 @@ Usage:
 Parsers:
 '''
 
+slicetext_string: str = '''\
+Slice:
+    [start]:[end]
+
+        start: [[-]index] - Zero-based start line, negative index for
+                counting from the end
+
+        end:   [[-]index] - Zero-based end line (excluding the index),
+                negative index for counting from the end
+'''
+
 helptext_end_string: str = '''\
 Examples:
     Standard Syntax:
@@ -90,7 +101,8 @@ Examples:
         $ jc --pretty /proc/meminfo
 
     Line Slicing:
-        $ cat file.csv | jc :101 --csv    # parse first 100 lines
+        $ $ cat output.txt | jc 4:15 --parser    # Parse from line 4 to 14
+                                                   with parser (zero-based)
 
     Parser Documentation:
         $ jc --help --dig