Most people believe escaping arguments to a process is easy. Surround it with quotes, right? Escape the quotes and surround it with quotes? Escape the quotes and backslashes and then surround it with quotes? When do you need to escape and quote an argument?
You need to escape and quote any string that either contains whitespace, or a quote. These are interpreted as a single quote character unless quoted and escaped.
So to make life easier, just escape anything with whitespace or a quote. How do you escape a command line argument? You will also need to escape all the quote characters, again by prefixing a new backslash.
Performance wasn't exactly a major consideration here since spawning the process will be several orders of magnitude more time consuming. If your interested, the following are some of the test patterns used. The above method was also tested with random arguments used to spawn a process that echoed each argument back for verification. Aug 20 Tagged with: argsargumentscommandprocessprogram.
The following characters have special meaning to the shell itself in some contexts and may need to be escaped in arguments:. Escaping a newline requires quoting — backslashes won't do the job. Any other characters listed in IFS will need similar handling. Some of these characters have tighter limits on when they truly need escaping than others.
It doesn't hurt to escape them all conservatively anyway, and it's easier than remembering the fine distinctions. If your command name itself is a shell keyword iffordo then you'll need to escape or quote it too.
The only interesting one of those is inbecause it's not obvious that it's always a keyword. You don't need to do that for keywords used in arguments, only when you've foolishly! In most common, sensible locales, at least those based on C or UTF-8, it's only the whitespace characters above. If you're dealing with an arbitrary unknown locale, it could include just about anything, including letters, so good luck.
Conceivably, a single byte considered blank could appear within a multi-byte character that wasn't blank, and you'd have no way to escape that other than putting the whole thing in quotes.
This behaviour depends on the locale configuration in the environment running the script, not the one where you wrote it. I think this behaviour is broken multiple ways, but we have to play the hand we're dealt. If you're working with any non-self-synchronising multibyte character set, the safest thing would be to quote everything. If you're in UTF-8 or C, you're safe for the moment.
It is tested in bashdashashkshzshand fish. Some of the characters do not need quoting in some versions of the shells, but the above works in all tested shells.
For lightweight escaping solution in Perl, I'm following the principle of single quotes. A Bash-string in single quotes can have any character, except the single quote itself.03 - Unix Shell Scripts - Command Line Arguments
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Ask Question. Asked 4 years ago. Active 2 years, 2 months ago. Viewed 17k times. Tim Tim Could you exhaustively list the kinds of characters which need to be escaped in cmd line args? The list is good to have, but the most important thing to understand about quoting, is: Everything between single quotes is passed literally and without word splitting. No exceptions. This means there is no way whatsoever to embed a single quote within single quotes, by the way, but that's easy to work around.
Active Oldest Votes.At one time or another, we all need to pass arbitrary command line arguments to some program. These arguments could be filenames, debugging flags, hostnames, or any other kind of information: the point is that we are to take a string and make sure some child program receives exactly that string in its argv array no matter what this string contains. The task is harder than it appears. For better or for worse 1Windows knows about only one command line string for each process.
Because one string is not terribly useful, libraries conspire to provide the illusion of multiple command line arguments: before creating a subprocess, a program combines all argument strings into one command line string, and the newly-born subprocess, before calling main, splits this string into arguments and passes the arguments as argv. In principle, each program can parse the command line string differently, but most use the convetion that CommandLineToArgvW and the Microsoft C library understand.
This convention is a good one because it provides a way to encode any command line argument as part of a command line string without losing information. Our first instinct should be look for a library function that's already solved the problem.
These functions appear to be precisely what we need: they take an arbitrary number of distinct command line arguments and promise to launch a subprocess. Unfortunately and counter-intuitively, these functions do not quote or process these arguments: instead, they're all concatenated into a single string, with arguments separated spaces, and this string is then passed to the child, where it's eventually interpreted by CommandLineToArgvW. This approach works only for arguments that do not themselves contain spaces.
That's not what we want! So, while the C runtime process-launching functions appear to be what we need, they're actually useless for solving the command line argument problem. Having seen the problems with the previous approach, one might suggest that we heed the advice provided in the the C runtime documentation and surround arguments containing spaces with double-quote characters. This solution is also wrong. Recall 2 that the CommandLineToArgV convention 3 stipulates that arguments containing spaces be surrounded by double quotation marks.
Following the above approach and surrounding arguments with quotation marks produces good results for simple cases, and many people stop here. So far, so good: but what if our arguments are more complex? Bear in mind that our convention also stipulates that we precede a double quotation mark that is part of an argument with a backslash, and that we precede with another backslash a backslash that precedes a quotation mark which itself actually terminates the argument and is not included as part of that argument 4.
So, if we follow our simplistic approach above and use this as our command line:. Many popular programs including command shells, the authors of which really should know better use this simple approach. Developers test only with simple argument strings, leaving users confused and puzzled when their command lines are occasionally mangled.
We've seen that properly quoting an arbitrary command line argument is non-trivial, and that doing it incorrectly causes subtle and maddening problems. The function below properly quotes an argument; translate it into your language and coding style of choice. To construct a command line string for a program from arbitrary arguments, we encode each argument including the program name with the above function and follow all but the last with a single space.
We can then pass the resulting string as the lpCommandLine parameter to CreateProcess and be confident that the child process will decode each argument to exactly the arguments we were initially given. One might conclude that we're done: after all, we now understand how to send arbitrary strings through CreateProcess so that they emerge unchanged on the other side but life is not that simple.
Often, we can't directly supply our command line CreateProcess, but instead must pass it through a level of indirection before reaching our intended child process.Parameter expansion will treat a Full Stop within a directory name as a file extension, so for a name like " Sample 2.
The CMD shell does not read file descriptors, or work with filesystem objects the way that PowerShell does, it is processing a simple list of text strings. Tokenization Tokenization of the command line arguments is not always done by the cmd. Most often the tokenization is done by the newly formed processes' runtime, at the OS level, Windows passes a command line untokenized as a single string to the new process.
In addition to passing numeric or string values on the command line, it is also possible to pass a variable name and then use the variable to transfer data between scripts or subroutines. Passing by reference is a slightly more advanced technique but can be particularly useful when the string contains characters that are CMD delimiters or quotes.
The expansion of a file attribute produces a series of 9 dashes, with each recognized attribute replacing a dash with a letter. A file with no recognized attributes or with none set will expand to 9 dashes like this: Example: Expansion of a file with the Hidden and System attributes: hs The maximum length of any command line or variable within CMD is characters.
In mathematical terms a parameter is "a numerical or other measurable factor" so typically a number. In programming terminology: A parameter represents a value that the procedure expects you to pass when you call it.
An argument represents the actual value that you pass to a procedure. In practice the phrases argument and parameter tend to be used interchangeably, CMD batch files do not perform any type checking. The FOR command creates parameter variables which are identified with a letter rather than a number e. The Parameter Expansions described above can also be applied to these. Examples: Pass parameters from one batch to another: MyBatch.
Issues with SQLCMD when using special characters
CALL - Call one batch program from another. FOR - Conditionally perform a command several times. StackOverflow - Script to parse optional arguments by Dave Benham. EXE parse scripts? Equivalent bash command Linux : dirname - Convert a full pathname to just a path.It can be used in distributed, heterogeneous environments, where automation requires using different technologies and interfaces.
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The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Question : Given a file name and an arbitrary list of strings, is there a canonical way to create a single command line such that Environment.
Background : The way. NET splits a command line into arguments is surprisingly complexe. If a double quotation mark follows two or an even number of backslashes, each proceeding backslash pair is replaced with one backslash and the double quotation mark is removed. If a double quotation mark follows an odd number of backslashes, including just one, each preceding pair is replaced with one backslash and the remaining backslash is removed; however, in this case the double quotation mark is not removed.
Many try the simple "put every argument in double quotes and escape existing double quotes" approach and fail as soon as one of the arguments contains a trailing backslash. There have been various questions on StackOverflow regarding this issue, e. However, their answers are either not general enough to provide a canonical solution for all cases or appear to be developed "iteratively" "Oh, there's one more special case I forgot, let's add it and now it should cover most cases Since this is quite a common problem, I'd like to see a solution that provides confidence, for example, by either.
This algorithm is generic and comes from a relatively authoritative source MSDN blogs. A few years ago, Microsoft announced that they were going to release a command line parser on CodePlex instead of the System. CommandLine that was supposed to ship with.
NET Framework 4. I'm not sure if they actually did this. If you want a parser developed by a Microsoft employee have a look at cmdline. Also you can look for command line parses in CodePlex. You could also try Mono. Options which is quite powerful. Learn more. Canonical solution for escaping. NET command line arguments Ask Question.
Asked 7 years, 4 months ago. Active 7 years, 4 months ago. Viewed 3k times. Start Passing command-line arguments in C However, their answers are either not general enough to provide a canonical solution for all cases or appear to be developed "iteratively" "Oh, there's one more special case I forgot, let's add it and now it should cover most cases Since this is quite a common problem, I'd like to see a solution that provides confidence, for example, by either coming from an authoritative source maybe a blog entry from one of the developers involved in this crazy command line convention or providing a formal proof that the given algorithm satisfies the.
NET command line requirements. Heinzi Heinzi k 46 46 gold badges silver badges bronze badges. Pursuing a generic solution to this problem is very unproductive. Write data to a file, pass the path of the file instead. I agree with Hans. What would you do with the solution once you had it? HansPassant: You don't always have control over the called application and many applications out there today do use multiple command-line arguments.
I want to pass the command line arguments string args to another process using ProcessInfo. The problem is that I get the arguments as an array and must merge them into a single string. An arguments could be crafted to trick my program. According to this answer I have created the following function to escape a single argument, but I might have missed something.
I was having related problem writing front-end. Initially all seemed good doing it as you suggest arg. We have been overzealous in escapes windows is not unix! Which we can do like so:. We did the encoding correctly but there is a twist because you are enclosing all parameters in double-quotes in case there are spaces in some of them.
My answer was similar to Nas Banov's answer but I wanted double quotes only if necessary. To escape the backslashes and double quotes correctly you can just replace any instances of multiple backslashes followed by a single double quote with:. If there was originally backslashes on the end of the argument they will not have been quoted, now that there is a double quote on the end they need to be.
So they are duplicated, which quotes them all, and prevents unintentionally quoting the final double quote. It does a minimal matching for the first section so that the last. I was running into issues with this, too. Instead of unparsing args, I went with taking the full original commandline and trimming off the executable.
It still has to chase escapes in the executable, but that seemed easier than the args. It works fine, but you should note that cmd. If and only iflike the original author of article noted your command line will be interpreted by cmd. There is a CommandLineEncoder.
Does a nice job of adding arguments, but doesn't escape. Added comment in method where escape sequence should go. This solved it. Learn more. Escape command line arguments in c Ask Question.