lib/rcstring/quote_shell.cc

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//
// nis-util - NIS Administration Utilities
// Copyright (C) 2012 Peter Miller
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or (at
// your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License along
// with this program. If not, see <http://www.gnu.org/licenses/>.
//

#include <lib/ac/ctype.h>

#include <lib/rcstring.h>
#include <lib/rcstring/accumulator.h>


rcstring
rcstring::quote_shell(void)
    const
{
    //
    // Work out if the string needs quoting.
    // and how long the output will be.
    //
    const char *start = c_str();
    const char *end = start + size();
    bool single_quotes = false;
    bool double_quotes = false;
    unsigned char mode = '\0';
    for (const char *cp = start; cp < end; ++cp)
    {
        unsigned char c = *cp;
        switch (c)
        {
        default:
            if (!isprint(c))
            {
                single_quotes = true;
                if (!mode)
                    mode = '\'';
            }
            break;


        case '\'':
            double_quotes = true;
            if (!mode)
                mode = '"';
            break;

        case '!':
            // The exclamation mark is special for bash and csh, and can
            // only be quoted with single quotes.
            //
            // Fall through...

        case '"': case '$': case '\\':
        case '`': case '~':
            single_quotes = true;
            if (!mode)
                mode = '\'';
            break;

        case '\t': case ' ': case '#': case '&': case '(': case ')': case '*':
        case ':': case ';': case '<': case '=': case '>': case '?': case '[':
        case ']': case '^': case '{': case '|': case '}':
            single_quotes = true;
            double_quotes = true;
            break;
        }
    }

    //
    // If it doesn't need quoting, just pass it through.
    //
    if (!single_quotes && !double_quotes)
    {
        return rcstring(start, size());
    }

    //
    // If we have a choice, use single quote mode,
    // it's usually shorter and it's easier to read.
    //
    if (!mode)
    {
        // Only use double quotes if we have to.
        mode = (double_quotes ? '"' : '\'');
    }

    //
    // Form the quoted string, using the minimum number of escapes.
    //
    // The gotcha here is the backquote: the `blah` substitution is
    // still active within double quotes.  And so are a few others.
    //
    // Also, there are some difficulties: the single quote can't be
    // quoted within single quotes, and the exclamation mark can't
    // be quoted by anything *except* single quotes.  Sheesh.
    //
    // Also, the rules change depending on which style of quoting
    // is in force at the time.
    //
    rcstring_accumulator buf;
    buf.push_back(mode);
    for (const char *cp = start; cp < end; ++cp)
    {
        unsigned char c = *cp;
        if (mode == '\'')
        {
            // within single quotes
            if (c == '\'')
            {
                //
                // You can't quote a single quote within single quotes.
                // Need to change to double quote mode.
                //
                buf.push_back("'\"'", 3);
                mode = '"';
            }
            else
                buf.push_back(c);
        }
        else
        {
            // within double quotes
            switch (c)
            {
            case '!':
                //
                // You can't quote an exclamation mark within double
                // quotes.  Need to change to single quote mode.
                //
                buf.push_back("\"'!", 3);
                mode = '\'';
                break;

            case '\n':
            case '"':
            case '\\':
            case '`': // stop command substitutions
            case '$': // stop variable substitutions
                buf.push_back('\\');
                // fall through...

            default:
                buf.push_back(c);
                break;
            }
        }
    }
    buf.push_back(mode);
    return buf.mkstr();
}


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