| CommandLine 2.0 Library Manual | -
Written by Chris Lattner
-
+
| -Introduction - |
This document describes the CommandLine argument processing library. It will show you how to use it, and what it can do. The CommandLine library uses a declarative approach to specifying the command line options that your program takes. By default, these options declarations implicitly hold the value parsed for the option declared (of course this can be -changed).
+changed).
-Although there are a lot of command line argument parsing libraries out -there in many different languages, none of them fit well with what I needed. By -looking at the features and problems of other libraries, I designed the -CommandLine library to have the following features:+
Although there are a lot of command line argument parsing libraries +out there in many different languages, none of them fit well with what I needed. +By looking at the features and problems of other libraries, I designed the +CommandLine library to have the following features:
+performance).
+error prone constructs, it also leads to dramatically cleaner source code.
+parser. This means that you don't have to write any boilerplate +code.
+loaded options trivial.
+assigned a value that is not valid for your enum type.
+arguments. This is possible because CommandLine is...
+you declare it. Custom parsers are no problem.
+tool. Additionally, it does most of the basic correctness checking for +you.
+href="#cl::ConsumeAfter">interpreter style options.
- +
This document will hopefully let you jump in and start using CommandLine in +your utility quickly and painlessly. Additionally it should be a simple +reference manual to figure out how stuff works. If it is failing in some area +(or you want an extension to the library), nag the author, Chris Lattner.
+| -Quick Start Guide - |
This section of the manual runs through a simple CommandLine'ification of a basic compiler tool. This is intended to show you how to jump into using the CommandLine library in your own program, and show you some of the cool things it -can do.
+can do.
-To start out, you need to include the CommandLine header file into your -program:+
To start out, you need to include the CommandLine header file into your +program:
-- #include "Support/CommandLine.h" -
+
+ #include "llvm/Support/CommandLine.h" +
+
Additionally, you need to add this as the first line of your main +program:
-+-... which actually parses the arguments and fills in the variable -declarations.int main(int argc, char **argv) { cl::ParseCommandLineOptions(argc, argv); ... } -+
+
... which actually parses the arguments and fills in the variable +declarations.
-Now that you are ready to support command line arguments, we need to tell the +Now that you are ready to support command line arguments, we need to tell the system which ones we want, and what type of argument they are. The CommandLine library uses a declarative syntax to model command line arguments with the global variable declarations that capture the parsed values. This means that @@ -190,65 +223,65 @@ for every command line option that you would like to support, there should be a global variable declaration to capture the result. For example, in a compiler, we would like to support the unix standard '-o <filename>' option to specify where to put the output. With the CommandLine library, this is -represented like this:
+represented like this:
-+ +-This declares a global variable "OutputFilename" that is used to +cl::opt<string> OutputFilename("o", cl::desc("Specify output filename"), cl::value_desc("filename")); -+
This declares a global variable "OutputFilename" that is used to capture the result of the "o" argument (first parameter). We specify that this is a simple scalar option by using the "cl::opt" template (as opposed to the "cl::list template), and tell the CommandLine library -that the data type that we are parsing is a string.
+that the data type that we are parsing is a string.
-The second and third parameters (which are optional) are used to specify what to -output for the "--help" option. In this case, we get a line that looks -like this:+
The second and third parameters (which are optional) are used to specify what +to output for the "--help" option. In this case, we get a line that +looks like this:
-+-Because we specified that the command line option should parse using the +USAGE: compiler [options] OPTIONS: -help - display available options (--help-hidden for more) -o <filename> - Specify output filename -+Because we specified that the command line option should parse using the string data type, the variable declared is automatically usable as a real string in all contexts that a normal C++ string object may be used. For -example:
+example:
-+-There are many different options that you can use to customize the command line -option handling library, but the above example shows the general interface to -these options. The options can be specified in any order, and are specified +... ofstream Output(OutputFilename.c_str()); if (Out.good()) ... ... -+
There are many different options that you can use to customize the command +line option handling library, but the above example shows the general interface +to these options. The options can be specified in any order, and are specified with helper functions like cl::desc(...), so there are no positional dependencies to remember. The available options are -discussed in detail in the Reference Guide.
+discussed in detail in the Reference Guide.
- -Continuing the example, we would like to have our compiler take an input +Continuing the example, we would like to have our compiler take an input filename as well as an output filename, but we do not want the input filename to be specified with a hyphen (ie, not -filename.c). To support this style of argument, the CommandLine library allows for positional arguments to be specified for the program. These positional arguments are filled with command line parameters that are not -in option form. We use this feature like this:
+in option form. We use this feature like this:
-+-This declaration indicates that the first positional argument should be treated -as the input filename. Here we use the This declaration indicates that the first positional argument should be +treated as the input filename. Here we use the cl::init option to specify an initial value for the command line option, which is used if the option is not specified (if you do not specify a cl::init modifier for an option, then @@ -256,89 +289,91 @@ the default constructor for the data type is used to initialize the value). Command line options default to being optional, so if we would like to require that the user always specify an input filename, we would add the cl::Required flag, and we could eliminate the -cl::init modifier, like this:cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-")); -++cl::init modifier, like this:
-+-Again, the CommandLine library does not require the options to be specified in -any particular order, so the above declaration is equivalent to:cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::Required); -++
Again, the CommandLine library does not require the options to be specified +in any particular order, so the above declaration is equivalent to:
-+-By simply adding the cl::Required flag, the -CommandLine library will automatically issue an error if the argument is not +cl::opt<string> InputFilename(cl::Positional, cl::Required, cl::desc("<input file>")); -+By simply adding the cl::Required flag, +the CommandLine library will automatically issue an error if the argument is not specified, which shifts all of the command line option verification code out of your application into the library. This is just one example of how using flags can alter the default behaviour of the library, on a per-option basis. By adding one of the declarations above, the --help option synopsis is now -extended to:
+extended to:
-++USAGE: compiler [options] <input file> OPTIONS: -help - display available options (--help-hidden for more) -o <filename> - Specify output filename -- -... indicating that an input filename is expected.+
... indicating that an input filename is expected.
+
| -Boolean Arguments - |
In addition to input and output filenames, we would like the compiler example +to support three boolean flags: "-f" to force overwriting of the output file, "--quiet" to enable quiet mode, and "-q" for backwards compatibility with some of our users. We can support these by declaring options -of boolean type like this:
+of boolean type like this:
-+-This does what you would expect: it declares three boolean variables +cl::opt<bool> Force ("f", cl::desc("Overwrite output files")); cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); cl::opt<bool> Quiet2("q", cl::desc("Don't print informational messages"), cl::Hidden); -+
This does what you would expect: it declares three boolean variables ("Force", "Quiet", and "Quiet2") to recognize these options. Note that the "-q" option is specified with the "cl::Hidden" flag. This modifier prevents it from being shown by the standard "--help" output (note that it is still -shown in the "--help-hidden" output).
+shown in the "--help-hidden" output).
-The CommandLine library uses a different parser +The CommandLine library uses a different parser for different data types. For example, in the string case, the argument passed to the option is copied literally into the content of the string variable... we obviously cannot do that in the boolean case, however, so we must use a smarter parser. In the case of the boolean parser, it allows no options (in which case it assigns the value of true to the variable), or it allows the values "true" or "false" to be specified, allowing any of the -following inputs:
+following inputs:
-+-... you get the idea. The bool parser just turns the -string values into boolean values, and rejects things like 'compiler +compiler -f # No value, 'Force' == true compiler -f=true # Value specified, 'Force' == true compiler -f=TRUE # Value specified, 'Force' == true compiler -f=FALSE # Value specified, 'Force' == false -+... you get the idea. The bool parser just turns +the string values into boolean values, and rejects things like 'compiler -f=foo'. Similarly, the float, double, and int parsers work like you would expect, using the 'strtol' and 'strtod' C -library calls to parse the string value into the specified data type.
+library calls to parse the string value into the specified data type.
-With the declarations above, "compiler --help" emits this:+
With the declarations above, "compiler --help" emits this:
-+-and "opt --help-hidden" prints this:USAGE: compiler [options] <input file> OPTIONS: @@ -346,11 +381,11 @@ OPTIONS: -o - Override output filename -quiet - Don't print informational messages -help - display available options (--help-hidden for more) -+
+
and "opt --help-hidden" prints this:
-+-This brief example has shown you how to use the 'This brief example has shown you how to use the 'cl::opt' class to parse simple scalar command line arguments. In addition to simple scalar arguments, the CommandLine library also provides primitives to support CommandLine option aliases, -and lists of options.USAGE: compiler [options] <input file> OPTIONS: @@ -359,98 +394,105 @@ OPTIONS: -q - Don't print informational messages -quiet - Don't print informational messages -help - display available options (--help-hidden for more) -+
+and lists of options.
+
| -Argument Aliases - |
+
+So far, the example works well, except for the fact that we need to check the +quiet condition like this now:
+ +-... which is a real pain! Instead of defining two values for the same +... if (!Quiet && !Quiet2) printInformationalMessage(...); ... -+
... which is a real pain! Instead of defining two values for the same condition, we can use the "cl::alias" class to make the "-q" option an alias for the "-quiet" option, instead of providing -a value itself:
+a value itself:
-+-The third line (which is the only one we modified from above) defines a +cl::opt<bool> Force ("f", cl::desc("Overwrite output files")); cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); cl::alias QuietA("q", cl::desc("Alias for -quiet"), cl::aliasopt(Quiet)); -+
The third line (which is the only one we modified from above) defines a "-q alias that updates the "Quiet" variable (as specified by the cl::aliasopt modifier) whenever it is specified. Because aliases do not hold state, the only thing the program has to query is the Quiet variable now. Another nice feature of aliases is that they automatically hide themselves from the -help output (although, again, they are still visible in the --help-hidden -output).
+output).
-Now the application code can simply use:+
Now the application code can simply use:
-++... if (!Quiet) printInformationalMessage(...); ... -- -... which is much nicer! The "cl::alias" can be used to specify an -alternative name for any variable type, and has many uses.
+
... which is much nicer! The "cl::alias" +can be used to specify an alternative name for any variable type, and has many +uses.
+
| -Selecting an alternative from a set of possibilities - |
So far, we have seen how the CommandLine library handles builtin types like std::string, bool and int, but how does it handle -things it doesn't know about, like enums or 'int*'s?
+things it doesn't know about, like enums or 'int*'s?
-The answer is that it uses a table driven generic parser (unless you specify +The answer is that it uses a table driven generic parser (unless you specify your own parser, as described in the Extension -Guide). This parser maps literal strings to whatever type is required, are -requires you to tell it what this mapping should be.
+Guide). This parser maps literal strings to whatever type is required, and +requires you to tell it what this mapping should be.
-Lets say that we would like to add four optimizations levels to our optimizer, -using the standard flags "-g", "-O0", "-O1", and -"-O2". We could easily implement this with boolean options like above, -but there are several problems with this strategy:+
Lets say that we would like to add four optimization levels to our +optimizer, using the standard flags "-g", "-O0", +"-O1", and "-O2". We could easily implement this with boolean +options like above, but there are several problems with this strategy:
+ -To cope with these problems, we can use an enum value, and have the CommandLine -library fill it in with the appropriate level directly, which is used like -this:
+
To cope with these problems, we can use an enum value, and have the +CommandLine library fill it in with the appropriate level directly, which is +used like this:
-+-This declaration defines a variable "OptimizationLevel" of the +enum OptLevel { g, O1, O2, O3 }; @@ -461,23 +503,24 @@ enum OptLevel { clEnumVal(O1, "Enable trivial optimizations"), clEnumVal(O2, "Enable default optimizations"), clEnumVal(O3, "Enable expensive optimizations"), - 0)); + clEnumValEnd)); ... if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); ... -+
This declaration defines a variable "OptimizationLevel" of the "OptLevel" enum type. This variable can be assigned any of the values that are listed in the declaration (Note that the declaration list must be -terminated with the "0" argument!). The CommandLine library enforces +terminated with the "clEnumValEnd" argument!). The CommandLine +library enforces that the user can only specify one of the options, and it ensure that only valid enum values can be specified. The "clEnumVal" macros ensure that the command line arguments matched the enum values. With this option added, our -help output now is:
+help output now is:
-+-In this case, it is sort of awkward that flag names correspond directly to enum -names, because we probably don't want a enum definition named "g" in -our program. Because of this, we can alternatively write this example like -this:USAGE: compiler [options] <input file> OPTIONS: @@ -490,14 +533,14 @@ OPTIONS: -help - display available options (--help-hidden for more) -o <filename> - Specify output filename -quiet - Don't print informational messages -++
In this case, it is sort of awkward that flag names correspond directly to +enum names, because we probably don't want a enum definition named "g" +in our program. Because of this, we can alternatively write this example like +this:
-++enum OptLevel { Debug, O1, O2, O3 }; @@ -508,35 +551,37 @@ enum OptLevel { clEnumVal(O1 , "Enable trivial optimizations"), clEnumVal(O2 , "Enable default optimizations"), clEnumVal(O3 , "Enable expensive optimizations"), - 0)); + clEnumValEnd)); ... if (OptimizationLevel == Debug) outputDebugInfo(...); ... -- -By using the "clEnumValN" macro instead of "clEnumVal", we can -directly specify the name that the flag should get. In general a direct mapping -is nice, but sometimes you can't or don't want to preserve the mapping, which is -when you would use it.
+
By using the "clEnumValN" macro instead of "clEnumVal", we +can directly specify the name that the flag should get. In general a direct +mapping is nice, but sometimes you can't or don't want to preserve the mapping, +which is when you would use it.
+
| -Named Alternatives - |
Another useful argument form is a named alternative style. We shall use this style in our compiler to specify different debug levels that can be used. Instead of each debug level being its own switch, we want to support the following options, of which only one can be specified at a time: "--debug-level=none", "--debug-level=quick", "--debug-level=detailed". To do this, we use the exact same format as our optimization level flags, but we also specify an option name. For this -case, the code looks like this:
+case, the code looks like this:
-+-This definition defines an enumerated command line variable of type "enum +enum DebugLev { nodebuginfo, quick, detailed }; @@ -547,15 +592,15 @@ enum DebugLev { clEnumValN(nodebuginfo, "none", "disable debug information"), clEnumVal(quick, "enable quick debug information"), clEnumVal(detailed, "enable detailed debug information"), - 0)); -+ clEnumValEnd)); +This definition defines an enumerated command line variable of type "enum DebugLev", which works exactly the same way as before. The difference here is just the interface exposed to the user of your program and the help output by -the "--help" option:
+the "--help" option:
-+-Again, the only structural difference between the debug level declaration and -the optimiation level declaration is that the debug level declaration includes +USAGE: compiler [options] <input file> OPTIONS: @@ -572,90 +617,153 @@ OPTIONS: -help - display available options (--help-hidden for more) -o <filename> - Specify output filename -quiet - Don't print informational messages -+
Again, the only structural difference between the debug level declaration and +the optimization level declaration is that the debug level declaration includes an option name ("debug_level"), which automatically changes how the library processes the argument. The CommandLine library supports both forms so -that you can choose the form most appropriate for your application.
- +that you can choose the form most appropriate for your application.
+
| -Parsing a list of options - |
Now that we have the standard run of the mill argument types out of the way, lets get a little wild and crazy. Lets say that we want our optimizer to accept a list of optimizations to perform, allowing duplicates. For example, we might want to run: "compiler -dce -constprop -inline -dce -strip". In this case, the order of the arguments and the number of appearances is very important. This is what the "cl::list" template is for. First, start by defining an enum of the optimizations that you -would like to perform:
+would like to perform:
-+-Then define your "cl::list" variable:enum Opts { // 'inline' is a C++ keyword, so name it 'inlining' dce, constprop, inlining, strip }; -+
+
Then define your "cl::list" variable:
-+-This defines a variable that is conceptually of the type +cl::list<Opts> OptimizationList(cl::desc("Available Optimizations:"), cl::values( clEnumVal(dce , "Dead Code Elimination"), clEnumVal(constprop , "Constant Propagation"), clEnumValN(inlining, "inline", "Procedure Integration"), clEnumVal(strip , "Strip Symbols"), - 0)); -+ clEnumValEnd)); +
This defines a variable that is conceptually of the type "std::vector<enum Opts>". Thus, you can access it with standard -vector methods:
+vector methods:
-+-... to iterate through the list of options specified.for (unsigned i = 0; i != OptimizationList.size(); ++i) switch (OptimizationList[i]) ... -++
... to iterate through the list of options specified.
-Note that the "cl::list" template is completely general and may be used -with any data types or other arguments that you can use with the -"cl::opt" template. One especially useful way to use a list is to -capture all of the positional arguments together if there may be more than one -specified. In the case of a linker, for example, the linker takes several -'.o' files, and needs to capture them into a list. This is naturally -specified as:+
Note that the "cl::list" template is +completely general and may be used with any data types or other arguments that +you can use with the "cl::opt" template. One +especially useful way to use a list is to capture all of the positional +arguments together if there may be more than one specified. In the case of a +linker, for example, the linker takes several '.o' files, and needs to +capture them into a list. This is naturally specified as:
-+-This variable works just like a "vector<string>" object. As +... cl::list<std::string> InputFilenames(cl::Positional, cl::desc("<Input files>"), cl::OneOrMore); ... -+
This variable works just like a "vector<string>" object. As such, accessing the list is simple, just like above. In this example, we used the cl::OneOrMore modifier to inform the CommandLine library that it is an error if the user does not specify any .o files on our command line. Again, this just reduces the amount of -checking we have to do.
+checking we have to do.
+
Instead of collecting sets of options in a list, it is also possible to +gather information for enum values in a bit vector. The represention used by +the cl::bits class is an unsigned +integer. An enum value is represented by a 0/1 in the enum's ordinal value bit +position. 1 indicating that the enum was specified, 0 otherwise. As each +specified value is parsed, the resulting enum's bit is set in the option's bit +vector:
+ ++ bits |= 1 << (unsigned)enum; +
Options that are specified multiple times are redundant. Any instances after +the first are discarded.
+ +Reworking the above list example, we could replace +cl::list with cl::bits:
+ ++cl::bits<Opts> OptimizationBits(cl::desc("Available Optimizations:"), + cl::values( + clEnumVal(dce , "Dead Code Elimination"), + clEnumVal(constprop , "Constant Propagation"), + clEnumValN(inlining, "inline", "Procedure Integration"), + clEnumVal(strip , "Strip Symbols"), + clEnumValEnd)); +
To test to see if constprop was specified, we can use the +cl:bits::isSet function:
+ +
+ if (OptimizationBits.isSet(constprop)) {
+ ...
+ }
+It's also possible to get the raw bit vector using the +cl::bits::getBits function:
+ ++ unsigned bits = OptimizationBits.getBits(); +
Finally, if external storage is used, then the location specified must be of +type unsigned. In all other ways a cl::bits option is morally equivalent to a cl::list option.
+ +| -Adding freeform text to help output - |
As our program grows and becomes more mature, we may decide to put summary information about what it does into the help output. The help output is styled to look similar to a Unix man page, providing concise information about a program. Unix man pages, however often have a description about what @@ -664,19 +772,19 @@ argument to the cl::ParseCommandLineOptions call in main. This additional argument is then printed as the overview information for your program, allowing you to include any additional information -that you want. For example:
+that you want. For example:
-+-Would yield the help output: +int main(int argc, char **argv) { cl::ParseCommandLineOptions(argc, argv, " CommandLine compiler example\n\n" " This program blah blah blah...\n"); ... } -+
would yield the help output:
-++OVERVIEW: CommandLine compiler example This program blah blah blah... @@ -687,71 +795,81 @@ OPTIONS: ... -help - display available options (--help-hidden for more) -o <filename> - Specify output filename -- +
| -Reference Guide - |
+
Now that you know the basics of how to use the CommandLine library, this +section will give you the detailed information you need to tune how command line +options work, as well as information on more "advanced" command line option +processing capabilities.
+| -Positional Arguments - |
Positional arguments are those arguments that are not named, and are not specified with a hyphen. Positional arguments should be used when an option is specified by its position alone. For example, the standard Unix grep tool takes a regular expression argument, and an optional filename to search through (which defaults to standard input if a filename is not specified). -Using the CommandLine library, this would be specified as:
+Using the CommandLine library, this would be specified as:
-+-Given these two option declarations, the --help output for our grep -replacement would look like this:cl::opt<string> Regex (cl::Positional, cl::desc("<regular expression>"), cl::Required); cl::opt<string> Filename(cl::Positional, cl::desc("<input file>"), cl::init("-")); -++
Given these two option declarations, the --help output for our grep +replacement would look like this:
-+-... and the resultant program could be used just like the standard grep -tool.USAGE: spiffygrep [options] <regular expression> <input file> OPTIONS: -help - display available options (--help-hidden for more) -++
... and the resultant program could be used just like the standard +grep tool.
-Positional arguments are sorted by their order of construction. This means that -command line options will be ordered according to how they are listed in a .cpp -file, but will not have an ordering defined if they positional arguments are -defined in multiple .cpp files. The fix for this problem is simply to define -all of your positional arguments in one .cpp file.+
Positional arguments are sorted by their order of construction. This means +that command line options will be ordered according to how they are listed in a +.cpp file, but will not have an ordering defined if the positional arguments +are defined in multiple .cpp files. The fix for this problem is simply to +define all of your positional arguments in one .cpp file.
+
Sometimes you may want to specify a value to your positional argument that starts with a hyphen (for example, searching for '-foo' in a file). At first, you will have trouble doing this, because it will try to find an argument named '-foo', and will fail (and single quotes will not save you). -Note that the system grep has the same problem:
+Note that the system grep has the same problem:
-+-The solution for this problem is the same for both your tool and the system +$ spiffygrep '-foo' test.txt Unknown command line argument '-foo'. Try: spiffygrep --help' @@ -760,90 +878,157 @@ Note that the system grep has the same problem:grep: illegal option -- o grep: illegal option -- o Usage: grep -hblcnsviw pattern file . . . -
+
The solution for this problem is the same for both your tool and the system version: use the '--' marker. When the user specifies '--' on the command line, it is telling the program that all options after the '--' should be treated as positional arguments, not options. Thus, we -can use it like this:
+can use it like this:
-++$ spiffygrep -- -foo test.txt ...output... -+
Sometimes an option can affect or modify the meaning of another option. For + example, consider gcc's -x LANG option. This tells + gcc to ignore the suffix of subsequent positional arguments and force + the file to be interpreted as if it contained source code in language + LANG. In order to handle this properly , you need to know the + absolute position of each argument, especially those in lists, so their + interaction(s) can be applied correctly. This is also useful for options like + -llibname which is actually a positional argument that starts with + a dash.
+So, generally, the problem is that you have two cl::list variables + that interact in some way. To ensure the correct interaction, you can use the + cl::list::getPosition(optnum) method. This method returns the + absolute position (as found on the command line) of the optnum + item in the cl::list.
+The idiom for usage is like this:
+ +
+ static cl::list<std::string> Files(cl::Positional, cl::OneOrMore);
+ static cl::listlt;std::string> Libraries("l", cl::ZeroOrMore);
+
+ int main(int argc, char**argv) {
+ // ...
+ std::vector<std::string>::iterator fileIt = Files.begin();
+ std::vector<std::string>::iterator libIt = Libraries.begin();
+ unsigned libPos = 0, filePos = 0;
+ while ( 1 ) {
+ if ( libIt != Libraries.end() )
+ libPos = Libraries.getPosition( libIt - Libraries.begin() );
+ else
+ libPos = 0;
+ if ( fileIt != Files.end() )
+ filePos = Files.getPosition( fileIt - Files.begin() );
+ else
+ filePos = 0;
+
+ if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) {
+ // Source File Is next
+ ++fileIt;
+ }
+ else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) {
+ // Library is next
+ ++libIt;
+ }
+ else
+ break; // we're done with the list
+ }
+ }Note that, for compatibility reasons, the cl::opt also supports an + unsigned getPosition() option that will provide the absolute position + of that option. You can apply the same approach as above with a + cl::opt and a cl::list option as you can with two lists.
+The cl::ConsumeAfter formatting option is used to construct programs that use "interpreter style" option processing. With this style of option processing, all arguments specified after the last positional argument are treated as special interpreter arguments that are not -interpreted by the command line argument.
+interpreted by the command line argument.
-As a concrete example, lets say we are developing a replacement for the standard -Unix Bourne shell (/bin/sh). To run /bin/sh, first you -specify options to the shell itself (like -x which turns on trace +As a concrete example, lets say we are developing a replacement for the +standard Unix Bourne shell (/bin/sh). To run /bin/sh, first +you specify options to the shell itself (like -x which turns on trace output), then you specify the name of the script to run, then you specify arguments to the script. These arguments to the script are parsed by the bourne shell command line option processor, but are not interpreted as options to the -shell itself. Using the CommandLine library, we would specify this as:
+shell itself. Using the CommandLine library, we would specify this as:
-+-which automatically provides the help output:cl::opt<string> Script(cl::Positional, cl::desc("<input script>"), cl::init("-")); cl::list<string> Argv(cl::ConsumeAfter, cl::desc("<program arguments>...")); cl::opt<bool> Trace("x", cl::desc("Enable trace output")); -+
+
which automatically provides the help output:
-+-At runtime, if we run our new shell replacement as 'spiffysh -x test.sh -a --x -y bar', the Trace variable will be set to true, the +USAGE: spiffysh [options] <input script> <program arguments>... OPTIONS: -help - display available options (--help-hidden for more) -x - Enable trace output -+
At runtime, if we run our new shell replacement as `spiffysh -x test.sh +-a -x -y bar', the Trace variable will be set to true, the Script variable will be set to "test.sh", and the -Argv list will contain ["-a", "-x", "-y", "bar"], because -they were specified after the last positional argument (which is the script -name).
- -There are several limitations to when cl::ConsumeAfter options can be -specified. For example, only one cl::ConsumeAfter can be specified per -program, there must be at least one positional -argument specified, and the cl::ConsumeAfter option should be a cl::list option.
+Argv list will contain ["-a", "-x", "-y", "bar"], because they +were specified after the last positional argument (which is the script +name).
+There are several limitations to when cl::ConsumeAfter options can +be specified. For example, only one cl::ConsumeAfter can be specified +per program, there must be at least one positional +argument specified, there must not be any cl::list +positional arguments, and the cl::ConsumeAfter option should be a cl::list option.
+
| -Internal vs External Storage - |
By default, all command line options automatically hold the value that they parse from the command line. This is very convenient in the common case, especially when combined with the ability to define command line options in the -files that use them. This is called the internal storage model.
+files that use them. This is called the internal storage model.
-Sometimes, however, it is nice to separate the command line option processing +Sometimes, however, it is nice to separate the command line option processing code from the storage of the value parsed. For example, lets say that we have a '-debug' option that we would like to use to enable debug information across the entire body of our program. In this case, the boolean value controlling the debug code should be globally accessable (in a header file, for example) yet the command line option processing code should not be exposed to all of these clients (requiring lots of .cpp files to #include -CommandLine.h).
+CommandLine.h).
-To do this, set up your .h file with your option, like this for example:+
To do this, set up your .h file with your option, like this for example:
+// DebugFlag.h - Get access to the '-debug' command line option // @@ -859,64 +1044,71 @@ extern bool DebugFlag; // debug build, then the code specified as the option to the macro will be // executed. Otherwise it will not be. Example: // -// DEBUG(cerr << "Bitset contains: " << Bitset << "\n"); +// DOUT << "Bitset contains: " << Bitset << "\n"; // -#ifdef NDEBUG +#ifdef NDEBUG #define DEBUG(X) #else -#define DEBUG(X) \ - do { if (DebugFlag) { X; } } while (0) -#endif +#define DEBUG(X) do { if (DebugFlag) { X; } } while (0) +#endif+
This allows clients to blissfully use the DEBUG() macro, or the DebugFlag explicitly if they want to. Now we just need to be able to set the DebugFlag boolean when the option is set. To do this, we pass an additial argument to our command line argument processor, and we specify -where to fill in with the cl::location attribute:
+where to fill in with the cl::location +attribute:
+-bool DebugFlag; // the actual value +bool DebugFlag; // the actual value static cl::opt<bool, true> // The parser -Debug("debug", cl::desc("Enable debug output"), cl::Hidden, - cl::location(DebugFlag)); +Debug("debug", cl::desc("Enable debug output"), cl::Hidden, cl::location(DebugFlag));+
- +
In the above example, we specify "true" as the second argument to +the cl::opt template, indicating that the +template should not maintain a copy of the value itself. In addition to this, +we specify the cl::location attribute, so +that DebugFlag is automatically set.
+| -Option Attributes - |
+
This section describes the basic attributes that you can specify on +options.
+This option is specified in simple double quotes:
cl::opt<bool> Quiet("quiet"); -
+ + +
+program.
+example.
+the right order.)
+information.
+
+ +
+that does not support it.
| -Option Modifiers - |
Option modifiers are the flags and expressions that you pass into the constructors for cl::opt and cl::list. These modifiers give you the ability to tweak how options are parsed and how --help output is generated to fit -your application well.
+your application well.
-These options fall into five main catagories:+
These options fall into five main catagories:
+ specified +
It is not possible to specify two options from the same catagory (you'll get +a runtime error) to a single option, except for options in the miscellaneous catagory. The CommandLine library specifies defaults for all of these settings that are the most useful in practice and the most common, which mean that you -usually shouldn't have to worry about these.
+usually shouldn't have to worry about these.
++
The cl::NotHidden, cl::Hidden, and +cl::ReallyHidden modifiers are used to control whether or not an option +appears in the --help and --help-hidden output for the +compiled program:
+in both help listings.
-The cl::Hidden modifier (which is the
+
+the --help-hidden output.
This group of options is used to control how many time an option is allowed +(or required) to be specified on the command line of your program. Specifying a value for this setting allows the CommandLine library to do error checking for -you.
+you.
-The allowed values for this option group are:+
The allowed values for this option group are:
+allow either zero or one occurrence of the option to be specified.
-The cl::ZeroOrMore modifier (which is
-the default for the cl::list class) indicates
-that your program will allow the option to be specified zero or more times.
+
+
+
+
If an option is not specified, then the value of the option is equal to the value specified by the cl::init attribute. If the cl::init attribute is not specified, the -option value is initialized with the default constructor for the data type.
+option value is initialized with the default constructor for the data type.
-If an option is specified multiple times for an option of the cl::opt class, only the last value will be retained.+
If an option is specified multiple times for an option of the cl::opt class, only the last value will be +retained.
+This group of options is used to control whether or not the option allows a value to be present. In the case of the CommandLine library, a value is either specified with an equal sign (e.g. '-index-depth=17') or as a trailing -string (e.g. '-o a.out').
+string (e.g. '-o a.out').
-The allowed values for this option group are:+
The allowed values for this option group are:
+href="#cl::ValueRequired">cl::ValueRequired
+a.out' to work.
+
In general, the default values for this option group work just like you would want them to. As mentioned above, you can specify the cl::ValueDisallowed modifier to a boolean argument to restrict your command line parser. These options are mostly useful -when extending the library.
- +when extending the library.
++
The formatting option group is used to specify that the command line option +has special abilities and is otherwise different from other command line +arguments. As usual, you can only specify at most one of these arguments.
- -The cl::Positional modifier specifies -that this is a positional argument, that does not have a command line option -associated with it. See the Positional Arguments -section for more information.
- -The cl::ConsumeAfter modifier -specifies that this option is used to capture "interpreter style" arguments. See this section for more information.
- - -The cl::Prefix modifier specifies that this -option prefixes its value. With 'Prefix' options, there is no equal sign that -separates the value from the option name specified. This is useful for -processing odd arguments like '-lmalloc -L/usr/lib' in a linker tool. -Here, the 'l' and 'L' options are normal string (list) -options, that have the cl::Prefix modifier added to -allow the CommandLine library to recognize them. Note that cl::Prefix options must not have the cl::ValueDisallowed modifier specified.
-
-The cl::Grouping modifier is used to
-implement unix style tools (like ls) that have lots of single letter
+
+
+letters. Note that cl::Grouping
+options cannot have values.
+
The CommandLine library does not restrict how you use the cl::Prefix or cl::Grouping modifiers, but it is possible to +specify ambiguous argument settings. Thus, it is possible to have multiple +letter options that are prefix or grouping options, and they will still work as +designed.
-To do this, the CommandLine library uses a greedy algorithm to parse the input -option into (potentially multiple) prefix and grouping options. The strategy -basically looks like this:+
To do this, the CommandLine library uses a greedy algorithm to parse the +input option into (potentially multiple) prefix and grouping options. The +strategy basically looks like this:
+ +
input = OrigInput;
while (!isOption(input) && !input.empty()) input.pop_back();
}
-
+
}
++
The miscellaneous option modifiers are the only flags where you can specify +more than one flag from the set: they are not mutually exclusive. These flags +specify boolean properties that modify the option.
+more values (i.e. it is a cl::list option).
+
So far, these are the only two miscellaneous option modifiers.
+| -Top-Level Classes and Functions - |
+classes in detail.
+ +The cl::ParseCommandLineOptions function is designed to be called directly from main, and is used to fill in the values of all of the command line option variables once argc and argv are -available.
+available.
-The cl::ParseCommandLineOptions function requires two parameters +The cl::ParseCommandLineOptions function requires two parameters (argc and argv), but may also take an optional third parameter which holds additional extra text to emit when the ---help option is invoked.
+--help option is invoked.
+The cl::ParseEnvironmentOptions function has mostly the same effects +as cl::ParseCommandLineOptions, +except that it is designed to take values for options from an environment +variable, for those cases in which reading the command line is not convenient or +not desired. It fills in the values of all the command line option variables +just like cl::ParseCommandLineOptions +does.
+ +It takes three parameters: first, the name of the program (since +argv may not be available, it can't just look in argv[0]), +second, the name of the environment variable to examine, and third, the optional +additional extra text to emit when the +--help option is invoked.
+ +cl::ParseEnvironmentOptions will break the environment +variable's value up into words and then process them using +cl::ParseCommandLineOptions. +Note: Currently cl::ParseEnvironmentOptions does not support +quoting, so an environment variable containing -option "foo bar" will +be parsed as three words, -option, "foo, and bar", +which is different from what you would get from the shell with the same +input.
+ +The cl::SetVersionPrinter function is designed to be called +directly from main, and before +cl::ParseCommandLineOptions. Its use is optional. It simply arranges +for a function to be called in response to the --version option instead +of having the CommandLine library print out the usual version string +for LLVM. This is useful for programs that are not part of LLVM but wish to use +the CommandLine facilities. Such programs should just define a small +function that takes no arguments and returns void and that prints out +whatever version information is appropriate for the program. Pass the address +of that function to cl::SetVersionPrinter to arrange for it to be +called when the --version option is given by the user.
+ +The cl::opt class is the class used to represent scalar command line options, and is the one used most of the time. It is a templated class which can take up to three arguments (all except for the first have default values -though):
+though):
-+-The first template argument specifies what underlying data type the command line -argument is, and is used to select a default parser implementation. The second -template argument is used to specify whether the option should contain the -storage for the option (the default) or whether external storage should be used -to contain the value parsed for the option (see Internal vs -External Storage for more information).namespace cl { template <class DataType, bool ExternalStorage = false, class ParserClass = parser<DataType> > class opt; } -+
+
The first template argument specifies what underlying data type the command +line argument is, and is used to select a default parser implementation. The +second template argument is used to specify whether the option should contain +the storage for the option (the default) or whether external storage should be +used to contain the value parsed for the option (see Internal +vs External Storage for more information).
-The third template argument specifies which parser to use. The default value +The third template argument specifies which parser to use. The default value selects an instantiation of the parser class based on the underlying data type of the option. In general, this default works well for most applications, so this option is only used when using a custom parser.
+href="#customparser">custom parser.
+
The cl::list class is the class used to represent a list of command line options. It too is a templated class which can take up to three -arguments:
+arguments:
-+-This class works the exact same as the cl::opt -class, except that the second argument is the type of the external -storage, not a boolean value. For this class, the marker type 'bool' -is used to indicate that internal storage should be used.namespace cl { template <class DataType, class Storage = bool, class ParserClass = parser<DataType> > class list; } -+
+
This class works the exact same as the cl::opt class, except that the second argument is +the type of the external storage, not a boolean value. For this class, +the marker type 'bool' is used to indicate that internal storage should +be used.
+
+
+The cl::bits class is the class used to represent a list of command +line options in the form of a bit vector. It is also a templated class which +can take up to three arguments:
+ ++ ++namespace cl { + template <class DataType, class Storage = bool, + class ParserClass = parser<DataType> > + class bits; +} +This class works the exact same as the cl::lists class, except that the second argument +must be of type unsigned if external storage is used.
+ +
The cl::alias class is a nontemplated class that is used to form +aliases for other arguments.
+ +
namespace cl {
class alias;
}
-
+The cl::aliasopt attribute should be +used to specify which option this is an alias for. Alias arguments default to +being Hidden, and use the aliased options parser to do +the conversion from string to data.
-The cl::aliasopt attribute should be used -to specify which option this is an alias for. Alias arguments default to being -Hidden, and use the aliased options parser to do the -conversion from string to data.+
The cl::extrahelp class is a nontemplated class that allows extra +help text to be printed out for the --help option.
+ +
+namespace cl {
+ struct extrahelp;
+}
+To use the extrahelp, simply construct one with a const char* +parameter to the constructor. The text passed to the constructor will be printed +at the bottom of the help message, verbatim. Note that multiple +cl::extrahelp can be used, but this practice is discouraged. If +your tool needs to print additional help information, put all that help into a +single cl::extrahelp instance.
+For example:
+
+ cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n");
+| -Builtin parsers - |
Parsers control how the string value taken from the command line is +translated into a typed value, suitable for use in a C++ program. By default, +the CommandLine library uses an instance of parser<type> if the command line option specifies that it uses values of type 'type'. Because of this, custom option processing is specified with specializations of -the 'parser' class.
+the 'parser' class.
+ +The CommandLine library provides the following builtin parser +specializations, which are sufficient for most applications. It can, however, +also be extended to work with new data types and new ways of interpreting the +same data. See the Writing a Custom Parser for more +details on this type of library extension.
-The CommandLine library provides the following builtin parser specializations, -which are sufficient for most applications. It can, however, also be extended to -work with new data types and new ways of interpreting the same data. See the Writing a Custom Parser for more details on this type -of library extension.+
+for any data type.
+"false", "FALSE", "False", and "0".
+
+'0x' or '0X'.
+
| -Extension Guide - |
Although the CommandLine library has a lot of functionality built into it already (as discussed previously), one of its true strengths lie in its extensibility. This section discusses how the CommandLine library works under -the covers and illustrates how to do some simple, common, extensions.
+the covers and illustrates how to do some simple, common, extensions.
+| Writing a custom parser - |
One of the simplest and most common extensions is the use of a custom parser. As discussed previously, parsers are the portion of the CommandLine library that turns string input from the user into a -particular parsed data type, validating the input in the process.
+particular parsed data type, validating the input in the process.
-There are two ways to use a new parser:+
There are two ways to use a new parser:
- This approach has the advantage that users of your custom data type will - automatically use your custom parser whenever they define an option with a - value type of your data type. The disadvantage of this approach is that it - doesn't work if your fundemental data type is something that is already - supported.
+
Specialize the cl::parser template for +your custom data type.
+ +
This approach has the advantage that users of your custom data type will +automatically use your custom parser whenever they define an option with a value +type of your data type. The disadvantage of this approach is that it doesn't +work if your fundamental data type is something that is already supported.
+ ++
Write an independent class, using it explicitly from options that need +it.
- This approach works well in situations where you would line to parse an - option using special syntax for a not-very-special data-type. The drawback - of this approach is that users of your parser have to be aware that they are - using your parser, instead of the builtin ones.+
This approach works well in situations where you would line to parse an +option using special syntax for a not-very-special data-type. The drawback of +this approach is that users of your parser have to be aware that they are using +your parser, instead of the builtin ones.
-+ -To guide the discussion, we will discuss a custom parser that accepts file + + +
To guide the discussion, we will discuss a custom parser that accepts file sizes, specified with an optional unit after the numeric size. For example, we would like to parse "102kb", "41M", "1G" into the appropriate integer value. In this case, the underlying data type we want to parse into is 'unsigned'. We choose approach #2 above because we don't want to make -this the default for all unsigned options.
+this the default for all unsigned options.
-To start out, we declare our new FileSizeParser class:+
To start out, we declare our new FileSizeParser class:
-+-Our new class inherits from the cl::basic_parser template class to fill -in the default, boiler plate, code for us. We give it the data type that we -parse into (the last argument to the parse method so that clients of +struct FileSizeParser : public cl::basic_parser<unsigned> { // parse - Return true on error. bool parse(cl::Option &O, const char *ArgName, const std::string &ArgValue, unsigned &Val); }; -+
Our new class inherits from the cl::basic_parser template class to +fill in the default, boiler plate, code for us. We give it the data type that +we parse into (the last argument to the parse method so that clients of our custom parser know what object type to pass in to the parse method (here we -declare that we parse into 'unsigned' variables.
+declare that we parse into 'unsigned' variables.
-For most purposes, the only method that must be implemented in a custom parser -is the parse method. The parse method is called whenever the -option is invoked, passing in the option itself, the option name, the string to -parse, and a reference to a return value. If the string to parse is not well formed, the parser should output an error message and return true. Otherwise it should return false and set 'Val' to the parsed value. In our example, we implement parse as:+
For most purposes, the only method that must be implemented in a custom +parser is the parse method. The parse method is called +whenever the option is invoked, passing in the option itself, the option name, +the string to parse, and a reference to a return value. If the string to parse +is not well formed, the parser should output an error message and return true. +Otherwise it should return false and set 'Val' to the parsed value. In +our example, we implement parse as:
-+-This function implements a very simple parser for the kinds of strings we are +bool FileSizeParser::parse(cl::Option &O, const char *ArgName, const std::string &Arg, unsigned &Val) { const char *ArgStart = Arg.c_str(); @@ -1431,34 +1846,34 @@ parse, and a reference to a return value. If the string to parse is not well fo } } } -+
This function implements a very simple parser for the kinds of strings we are interested in. Although it has some holes (it allows "123KKK" for example), it is good enough for this example. Note that we use the option itself to print out the error message (the error method always returns true) in order to get a nice error message (shown below). Now that we have our -parser class, we can use it like this:
+parser class, we can use it like this:
-+-Which adds this to the output of our program:static cl::opt<unsigned, false, FileSizeParser> MFS("max-file-size", cl::desc("Maximum file size to accept"), cl::value_desc("size")); -+
+
Which adds this to the output of our program:
-+-And we can test that our parse works correctly now (the test program just prints -out the max-file-size argument value):OPTIONS: -help - display available options (--help-hidden for more) ... -max-file-size=<size> - Maximum file size to accept -+
+
And we can test that our parse works correctly now (the test program just +prints out the max-file-size argument value):
-+-It looks like it works. The error message that we get is nice and helpful, and -we seem to accept reasonable file sizes. This wraps up the "custom parser" -tutorial.$ ./test MFS: 0 $ ./test -max-file-size=123MB @@ -1467,41 +1882,57 @@ $ ./test -max-file-size=3G MFS: 3221225472 $ ./test -max-file-size=dog -max-file-size option: 'dog' value invalid for file size argument! -+
+
It looks like it works. The error message that we get is nice and helpful, +and we seem to accept reasonable file sizes. This wraps up the "custom parser" +tutorial.
+
| Exploiting external -storage |
Several of the LLVM libraries define static cl::opt instances that + will automatically be included in any program that links with that library. + This is a feature. However, sometimes it is necessary to know the value of the + command line option outside of the library. In these cases the library does or + should provide an external storage location that is accessible to users of the + library. Examples of this include the llvm::DebugFlag exported by the + lib/Support/Debug.cpp file and the llvm::TimePassesIsEnabled + flag exported by the lib/VMCore/Pass.cpp file.
+TODO: complete this section
- -| Dynamically adding command -line options |
TODO: fill in this section
+
+