echo: Add echo.py and test script

Author: Expertcoderz

src/echo.py

@@ -0,0 +1,83 @@
+#!/usr/bin/python3
+
+import codecs
+import re
+from optparse import OptionParser, BadOptionError, AmbiguousOptionError
+
+ESCAPES_PATTERN = re.compile(
+    r"(\\0[0-7]{1,3}|\\x[0-9A-Za-z]{1,2}|\\[\\0abcefnrtv])",
+    re.UNICODE | re.VERBOSE,
+)
+
+
+class PassthroughOptionParser(OptionParser):
+    """
+    A modified version of OptionParser that treats unknown options and "--" as
+    regular arguments. Always behaves as if interspersed args are disabled.
+    """
+
+    def _process_args(self, largs, rargs, values):
+        parsing_options = True
+
+        for arg in rargs:
+            if parsing_options and arg and arg[0] == "-" and arg != "--":
+                try:
+                    super()._process_args([], [arg], values)
+                except (BadOptionError, AmbiguousOptionError) as e:
+                    parsing_options = False
+                    largs.append(e.opt_str)
+            else:
+                parsing_options = False
+                largs.append(arg)
+
+        rargs.clear()
+
+
+def echo(opts, args):
+    string = " ".join(args)
+
+    if opts.escapes:
+
+        def decode_match(match: re.Match[str]) -> str:
+            try:
+                if (escape := match.group(0))[1] == "0" and len(escape) > 2:
+                    # Convert octal escapes from "\0NNN" to Python's form
+                    # ("\NNN" without the "0").
+                    escape = "\\" + escape[2:]
+
+                return codecs.decode(escape, "unicode_escape")
+            except UnicodeDecodeError:
+                return match.group(0)
+
+        string = ESCAPES_PATTERN.sub(decode_match, string)
+
+    print(string, end="" if opts.n else "\n")
+
+
+if __name__ == "__main__":
+    parser = PassthroughOptionParser(
+        usage="Usage: %prog [OPTION]... [STRING]...",
+        description="Print STRING(s) to standard output.",
+        add_help_option=False,
+    )
+    parser.disable_interspersed_args()
+    parser.add_option("--help", action="help", help="show usage information and exit")
+
+    parser.add_option(
+        "-n", action="store_true", help="do not output the trailing newline"
+    )
+    parser.add_option(
+        "-e",
+        dest="escapes",
+        action="store_true",
+        help="enable interpretation of backslash escapes",
+    )
+    parser.add_option(
+        "-E",
+        dest="escapes",
+        action="store_false",
+        default=False,
+        help="disable interpretation of backslash escapes (default)",
+    )
+
+    echo(*parser.parse_args())

tests/echo.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env sh
+
+set -eux
+
+## basic echo
+
+result="$(./echo.py foo bar)"
+
+test "${result}" = 'foo bar'
+
+## double hyphen
+
+result="$(./echo.py -- foo)"
+
+test "${result}" = '-- foo'
+
+## multiple double hyphens
+
+result="$(./echo.py -- foo --)"
+
+test "${result}" = '-- foo --'
+
+## unknown option
+
+result="$(./echo.py -x foo)"
+
+test "${result}" = '-x foo'
+
+## unknown option and double hyphen
+
+result="$(./echo.py -x -- foo)"
+
+test "${result}" = '-x -- foo'
+
+## escape codes
+
+result="$(./echo.py -e 'foo \x41' '\0102')"
+
+test "${result}" = 'foo A B'
+
+## no arguments
+
+result="$(./echo.py)"
+
+test "${result}" = "$(printf '\n')"
+
+## empty arguments
+
+result="$(./echo.py '' foo '' bar '' '')"
+
+test "${result}" = ' foo  bar  '
+
+## no trailing newline
+
+n_lines="$(./echo.py -n 'foo' | wc -l)"
+
+test "${n_lines}" = 0
+
+exit 0