shell_escape.py

def shell_escape(s, quote_empty=True):
    if quote_empty and s == '':
        return "''"
    squot = False
    dquot = False
    dquot_special = False
    special = False
    escaped = []
    for c in s:
        if c == "'":
            squot = True
            escaped.append("\\")
            escaped.append(c)
        elif c == '"':
            dquot = True
            dquot_special = True
            escaped.append("\\")
            escaped.append(c)
        elif c in '$`\\':
            special = True
            dquot_special = True
            escaped.append("\\")
            escaped.append(c)
        elif c in '{}[]()*~|;!#& =?<>':
            special = True
            escaped.append("\\")
            escaped.append(c)
        else:
            escaped.append(c)
    if not special:
        if not squot and not dquot:
            return s
        if squot and not dquot:
            return '"' + s + '"' if len(escaped) >= len(s) + 2 else ''.join(escaped)
        if dquot and not squot:
            return "'" + s + "'" if len(escaped) >= len(s) + 2 else ''.join(escaped)
        return "\\'".join(shell_escape(word, False) for word in s.split("'"))
    prefer_quotes = len(escaped) >= len(s) + 2
    if not squot and prefer_quotes:
        return "'" + s + "'"
    elif not dquot_special and prefer_quotes:
        return '"' + s + '"'
    else:
        return ''.join(escaped)

if __name__ == '__main__':
    cases = [
        '',
        ' ',
        '  ',
        '   ',
        'hello',
        'hello world',
        'hello world!',
        "I'm here?",
        "I'm here.",
        "I'm (not) spending any $$~",
        'He said, "This is a quote."',
        'Try [some] {braces}',
        '$(one command \'quote\')+`and another`'
    ]
    for case in cases:
        print(shell_escape(case))