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Published: Dec 8, 2014 License: BSD-3-Clause Imports: 35 Imported by: 0



Go is a tool for managing Go source code.


go command [arguments]

The commands are:

build       compile packages and dependencies
clean       remove object files
env         print Go environment information
fix         run go tool fix on packages
fmt         run gofmt on package sources
generate    generate Go files by processing source
get         download and install packages and dependencies
install     compile and install packages and dependencies
list        list packages
run         compile and run Go program
test        test packages
tool        run specified go tool
version     print Go version
vet         run go tool vet on packages

Use "go help [command]" for more information about a command.

Additional help topics:

c           calling between Go and C
filetype    file types
gopath      GOPATH environment variable
importpath  import path syntax
packages    description of package lists
testflag    description of testing flags
testfunc    description of testing functions

Use "go help [topic]" for more information about that topic.

Compile packages and dependencies


go build [-o output] [-i] [build flags] [packages]

Build compiles the packages named by the import paths, along with their dependencies, but it does not install the results.

If the arguments are a list of .go files, build treats them as a list of source files specifying a single package.

When the command line specifies a single main package, build writes the resulting executable to output. Otherwise build compiles the packages but discards the results, serving only as a check that the packages can be built.

The -o flag specifies the output file name. If not specified, the output file name depends on the arguments and derives from the name of the package, such as p.a for package p, unless p is 'main'. If the package is main and file names are provided, the file name derives from the first file name mentioned, such as f1 for 'go build f1.go f2.go'; with no files provided ('go build'), the output file name is the base name of the containing directory.

The -i flag installs the packages that are dependencies of the target.

The build flags are shared by the build, clean, get, install, list, run, and test commands:

	force rebuilding of packages that are already up-to-date.
	In Go releases, does not apply to the standard library.
	print the commands but do not run them.
-p n
	the number of builds that can be run in parallel.
	The default is the number of CPUs available.
	enable data race detection.
	Supported only on linux/amd64, freebsd/amd64, darwin/amd64 and windows/amd64.
	print the names of packages as they are compiled.
	print the name of the temporary work directory and
	do not delete it when exiting.
	print the commands.

-ccflags 'arg list'
	arguments to pass on each 5c, 6c, or 8c compiler invocation.
-compiler name
	name of compiler to use, as in runtime.Compiler (gccgo or gc).
-gccgoflags 'arg list'
	arguments to pass on each gccgo compiler/linker invocation.
-gcflags 'arg list'
	arguments to pass on each 5g, 6g, or 8g compiler invocation.
-installsuffix suffix
	a suffix to use in the name of the package installation directory,
	in order to keep output separate from default builds.
	If using the -race flag, the install suffix is automatically set to race
	or, if set explicitly, has _race appended to it.
-ldflags 'flag list'
	arguments to pass on each 5l, 6l, or 8l linker invocation.
-tags 'tag list'
	a list of build tags to consider satisfied during the build.
	For more information about build tags, see the description of
	build constraints in the documentation for the go/build package.

The list flags accept a space-separated list of strings. To embed spaces in an element in the list, surround it with either single or double quotes.

For more about specifying packages, see 'go help packages'. For more about where packages and binaries are installed, run 'go help gopath'. For more about calling between Go and C/C++, run 'go help c'.

See also: go install, go get, go clean.

Remove object files


go clean [-i] [-r] [-n] [-x] [build flags] [packages]

Clean removes object files from package source directories. The go command builds most objects in a temporary directory, so go clean is mainly concerned with object files left by other tools or by manual invocations of go build.

Specifically, clean removes the following files from each of the source directories corresponding to the import paths:

_obj/            old object directory, left from Makefiles
_test/           old test directory, left from Makefiles
_testmain.go     old gotest file, left from Makefiles
test.out         old test log, left from Makefiles
build.out        old test log, left from Makefiles
*.[568ao]        object files, left from Makefiles

DIR(.exe)        from go build
DIR.test(.exe)   from go test -c
MAINFILE(.exe)   from go build MAINFILE.go
*.so             from SWIG

In the list, DIR represents the final path element of the directory, and MAINFILE is the base name of any Go source file in the directory that is not included when building the package.

The -i flag causes clean to remove the corresponding installed archive or binary (what 'go install' would create).

The -n flag causes clean to print the remove commands it would execute, but not run them.

The -r flag causes clean to be applied recursively to all the dependencies of the packages named by the import paths.

The -x flag causes clean to print remove commands as it executes them.

For more about build flags, see 'go help build'.

For more about specifying packages, see 'go help packages'.

Print Go environment information


go env [var ...]

Env prints Go environment information.

By default env prints information as a shell script (on Windows, a batch file). If one or more variable names is given as arguments, env prints the value of each named variable on its own line.

Run go tool fix on packages


go fix [packages]

Fix runs the Go fix command on the packages named by the import paths.

For more about fix, see 'godoc fix'. For more about specifying packages, see 'go help packages'.

To run fix with specific options, run 'go tool fix'.

See also: go fmt, go vet.

Run gofmt on package sources


go fmt [-n] [-x] [packages]

Fmt runs the command 'gofmt -l -w' on the packages named by the import paths. It prints the names of the files that are modified.

For more about gofmt, see 'godoc gofmt'. For more about specifying packages, see 'go help packages'.

The -n flag prints commands that would be executed. The -x flag prints commands as they are executed.

To run gofmt with specific options, run gofmt itself.

See also: go fix, go vet.

Generate Go files by processing source


go generate [-run regexp] [file.go... | packages]

Generate runs commands described by directives within existing files. Those commands can run any process but the intent is to create or update Go source files, for instance by running yacc.

Go generate is never run automatically by go build, go get, go test, and so on. It must be run explicitly.

Go generate scans the file for directives, which are lines of the form,

//go:generate command argument...

(note: no leading spaces and no space in "//go") where command is the generator to be run, corresponding to an executable file that can be run locally. It must either be in the shell path (gofmt), a fully qualified path (/usr/you/bin/mytool), or a command alias, described below.

Note that go generate does not parse the file, so lines that look like directives in comments or multiline strings will be treated as directives.

The arguments to the directive are space-separated tokens or double-quoted strings passed to the generator as individual arguments when it is run.

Quoted strings use Go syntax and are evaluated before execution; a quoted string appears as a single argument to the generator.

Go generate sets several variables when it runs the generator:

	The execution architecture (arm, amd64, etc.)
	The execution operating system (linux, windows, etc.)
	The base name of the file.
	The name of the package of the file containing the directive.

Other than variable substitution and quoted-string evaluation, no special processing such as "globbing" is performed on the command line.

As a last step before running the command, any invocations of any environment variables with alphanumeric names, such as $GOFILE or $HOME, are expanded throughout the command line. The syntax for variable expansion is $NAME on all operating systems. Due to the order of evaluation, variables are expanded even inside quoted strings. If the variable NAME is not set, $NAME expands to the empty string.

A directive of the form,

//go:generate -command xxx args...

specifies, for the remainder of this source file only, that the string xxx represents the command identified by the arguments. This can be used to create aliases or to handle multiword generators. For example,

//go:generate -command yacc go tool yacc

specifies that the command "yacc" represents the generator "go tool yacc".

Generate processes packages in the order given on the command line, one at a time. If the command line lists .go files, they are treated as a single package. Within a package, generate processes the source files in a package in file name order, one at a time. Within a source file, generate runs generators in the order they appear in the file, one at a time.

If any generator returns an error exit status, "go generate" skips all further processing for that package.

The generator is run in the package's source directory.

Go generate accepts one specific flag:

	if non-empty, specifies a regular expression to
	select directives whose command matches the expression.

It also accepts the standard build flags -v, -n, and -x. The -v flag prints the names of packages and files as they are processed. The -n flag prints commands that would be executed. The -x flag prints commands as they are executed.

For more about specifying packages, see 'go help packages'.

Download and install packages and dependencies


go get [-d] [-f] [-fix] [-t] [-u] [build flags] [packages]

Get downloads and installs the packages named by the import paths, along with their dependencies.

The -d flag instructs get to stop after downloading the packages; that is, it instructs get not to install the packages.

The -f flag, valid only when -u is set, forces get -u not to verify that each package has been checked out from the source control repository implied by its import path. This can be useful if the source is a local fork of the original.

The -fix flag instructs get to run the fix tool on the downloaded packages before resolving dependencies or building the code.

The -t flag instructs get to also download the packages required to build the tests for the specified packages.

The -u flag instructs get to use the network to update the named packages and their dependencies. By default, get uses the network to check out missing packages but does not use it to look for updates to existing packages.

Get also accepts build flags to control the installation. See 'go help build'.

When checking out or updating a package, get looks for a branch or tag that matches the locally installed version of Go. The most important rule is that if the local installation is running version "go1", get searches for a branch or tag named "go1". If no such version exists it retrieves the most recent version of the package.

For more about specifying packages, see 'go help packages'.

For more about how 'go get' finds source code to download, see 'go help importpath'.

See also: go build, go install, go clean.

Compile and install packages and dependencies


go install [build flags] [packages]

Install compiles and installs the packages named by the import paths, along with their dependencies.

For more about the build flags, see 'go help build'. For more about specifying packages, see 'go help packages'.

See also: go build, go get, go clean.

List packages


go list [-e] [-f format] [-json] [build flags] [packages]

List lists the packages named by the import paths, one per line.

The default output shows the package import path:


The -f flag specifies an alternate format for the list, using the syntax of package template. The default output is equivalent to -f '{{.ImportPath}}'. The struct being passed to the template is:

type Package struct {
    Dir           string // directory containing package sources
    ImportPath    string // import path of package in dir
    ImportComment string // path in import comment on package statement
    Name          string // package name
    Doc           string // package documentation string
    Target        string // install path
    Goroot        bool   // is this package in the Go root?
    Standard      bool   // is this package part of the standard Go library?
    Stale         bool   // would 'go install' do anything for this package?
    Root          string // Go root or Go path dir containing this package

    // Source files
    GoFiles        []string // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
    CgoFiles       []string // .go sources files that import "C"
    IgnoredGoFiles []string // .go sources ignored due to build constraints
    CFiles         []string // .c source files
    CXXFiles       []string // .cc, .cxx and .cpp source files
    MFiles         []string // .m source files
    HFiles         []string // .h, .hh, .hpp and .hxx source files
    SFiles         []string // .s source files
    SwigFiles      []string // .swig files
    SwigCXXFiles   []string // .swigcxx files
    SysoFiles      []string // .syso object files to add to archive

    // Cgo directives
    CgoCFLAGS    []string // cgo: flags for C compiler
    CgoCPPFLAGS  []string // cgo: flags for C preprocessor
    CgoCXXFLAGS  []string // cgo: flags for C++ compiler
    CgoLDFLAGS   []string // cgo: flags for linker
    CgoPkgConfig []string // cgo: pkg-config names

    // Dependency information
    Imports []string // import paths used by this package
    Deps    []string // all (recursively) imported dependencies

    // Error information
    Incomplete bool            // this package or a dependency has an error
    Error      *PackageError   // error loading package
    DepsErrors []*PackageError // errors loading dependencies

    TestGoFiles  []string // _test.go files in package
    TestImports  []string // imports from TestGoFiles
    XTestGoFiles []string // _test.go files outside package
    XTestImports []string // imports from XTestGoFiles

The template function "join" calls strings.Join.

The template function "context" returns the build context, defined as:

type Context struct {
	GOARCH        string   // target architecture
	GOOS          string   // target operating system
	GOROOT        string   // Go root
	GOPATH        string   // Go path
	CgoEnabled    bool     // whether cgo can be used
	UseAllFiles   bool     // use files regardless of +build lines, file names
	Compiler      string   // compiler to assume when computing target paths
	BuildTags     []string // build constraints to match in +build lines
	ReleaseTags   []string // releases the current release is compatible with
	InstallSuffix string   // suffix to use in the name of the install dir

For more information about the meaning of these fields see the documentation for the go/build package's Context type.

The -json flag causes the package data to be printed in JSON format instead of using the template format.

The -e flag changes the handling of erroneous packages, those that cannot be found or are malformed. By default, the list command prints an error to standard error for each erroneous package and omits the packages from consideration during the usual printing. With the -e flag, the list command never prints errors to standard error and instead processes the erroneous packages with the usual printing. Erroneous packages will have a non-empty ImportPath and a non-nil Error field; other information may or may not be missing (zeroed).

For more about build flags, see 'go help build'.

For more about specifying packages, see 'go help packages'.

Compile and run Go program


go run [build flags] [-exec xprog] gofiles... [arguments...]

Run compiles and runs the main package comprising the named Go source files. A Go source file is defined to be a file ending in a literal ".go" suffix.

By default, 'go run' runs the compiled binary directly: 'a.out arguments...'. If the -exec flag is given, 'go run' invokes the binary using xprog: 'xprog a.out arguments...'. If the -exec flag is not given, GOOS or GOARCH is different from the system default, and a program named go_$GOOS_$GOARCH_exec can be found on the current search path, 'go run' invokes the binary using that program, for example 'go_nacl_386_exec a.out arguments...'. This allows execution of cross-compiled programs when a simulator or other execution method is available.

For more about build flags, see 'go help build'.

See also: go build.

Test packages


go test [-c] [-i] [build and test flags] [packages] [flags for test binary]

'Go test' automates testing the packages named by the import paths. It prints a summary of the test results in the format:

ok   archive/tar   0.011s
FAIL archive/zip   0.022s
ok   compress/gzip 0.033s

followed by detailed output for each failed package.

'Go test' recompiles each package along with any files with names matching the file pattern "*_test.go". Files whose names begin with "_" (including "_test.go") or "." are ignored. These additional files can contain test functions, benchmark functions, and example functions. See 'go help testfunc' for more. Each listed package causes the execution of a separate test binary.

Test files that declare a package with the suffix "_test" will be compiled as a separate package, and then linked and run with the main test binary.

By default, go test needs no arguments. It compiles and tests the package with source in the current directory, including tests, and runs the tests.

The package is built in a temporary directory so it does not interfere with the non-test installation.

In addition to the build flags, the flags handled by 'go test' itself are:

	Compile the test binary to pkg.test but do not run it
	(where pkg is the last element of the package's import path).
	The file name can be changed with the -o flag.

-exec xprog
    Run the test binary using xprog. The behavior is the same as
    in 'go run'. See 'go help run' for details.

    Install packages that are dependencies of the test.
    Do not run the test.

-o file
	Compile the test binary to the named file.
	The test still runs (unless -c or -i is specified).

The test binary also accepts flags that control execution of the test; these flags are also accessible by 'go test'. See 'go help testflag' for details.

If the test binary needs any other flags, they should be presented after the package names. The go tool treats as a flag the first argument that begins with a minus sign that it does not recognize itself; that argument and all subsequent arguments are passed as arguments to the test binary.

For more about build flags, see 'go help build'. For more about specifying packages, see 'go help packages'.

See also: go build, go vet.

Run specified go tool


go tool [-n] command [args...]

Tool runs the go tool command identified by the arguments. With no arguments it prints the list of known tools.

The -n flag causes tool to print the command that would be executed but not execute it.

For more about each tool command, see 'go tool command -h'.

Print Go version


go version

Version prints the Go version, as reported by runtime.Version.

Run go tool vet on packages


go vet [-n] [-x] [packages]

Vet runs the Go vet command on the packages named by the import paths.

For more about vet, see 'godoc golang.org/x/tools/cmd/vet'. For more about specifying packages, see 'go help packages'.

To run the vet tool with specific options, run 'go tool vet'.

The -n flag prints commands that would be executed. The -x flag prints commands as they are executed.

See also: go fmt, go fix.

Calling between Go and C

There are two different ways to call between Go and C/C++ code.

The first is the cgo tool, which is part of the Go distribution. For information on how to use it see the cgo documentation (godoc cmd/cgo).

The second is the SWIG program, which is a general tool for interfacing between languages. For information on SWIG see http://swig.org/. When running go build, any file with a .swig extension will be passed to SWIG. Any file with a .swigcxx extension will be passed to SWIG with the -c++ option.

When either cgo or SWIG is used, go build will pass any .c, .m, .s, or .S files to the C compiler, and any .cc, .cpp, .cxx files to the C++ compiler. The CC or CXX environment variables may be set to determine the C or C++ compiler, respectively, to use.

File types

The go command examines the contents of a restricted set of files in each directory. It identifies which files to examine based on the extension of the file name. These extensions are:

	Go source files.
.c, .h
	C source files.
	If the package uses cgo, these will be compiled with the
	OS-native compiler (typically gcc); otherwise they will be
	compiled with the Go-specific support compiler,
	5c, 6c, or 8c, etc. as appropriate.
.cc, .cpp, .cxx, .hh, .hpp, .hxx
	C++ source files. Only useful with cgo or SWIG, and always
	compiled with the OS-native compiler.
	Objective-C source files. Only useful with cgo, and always
	compiled with the OS-native compiler.
.s, .S
	Assembler source files.
	If the package uses cgo, these will be assembled with the
	OS-native assembler (typically gcc (sic)); otherwise they
	will be assembled with the Go-specific support assembler,
	5a, 6a, or 8a, etc., as appropriate.
.swig, .swigcxx
	SWIG definition files.
	System object files.

Files of each of these types except .syso may contain build constraints, but the go command stops scanning for build constraints at the first item in the file that is not a blank line or //-style line comment.

GOPATH environment variable

The Go path is used to resolve import statements. It is implemented by and documented in the go/build package.

The GOPATH environment variable lists places to look for Go code. On Unix, the value is a colon-separated string. On Windows, the value is a semicolon-separated string. On Plan 9, the value is a list.

GOPATH must be set to get, build and install packages outside the standard Go tree.

Each directory listed in GOPATH must have a prescribed structure:

The src/ directory holds source code. The path below 'src' determines the import path or executable name.

The pkg/ directory holds installed package objects. As in the Go tree, each target operating system and architecture pair has its own subdirectory of pkg (pkg/GOOS_GOARCH).

If DIR is a directory listed in the GOPATH, a package with source in DIR/src/foo/bar can be imported as "foo/bar" and has its compiled form installed to "DIR/pkg/GOOS_GOARCH/foo/bar.a".

The bin/ directory holds compiled commands. Each command is named for its source directory, but only the final element, not the entire path. That is, the command with source in DIR/src/foo/quux is installed into DIR/bin/quux, not DIR/bin/foo/quux. The foo/ is stripped so that you can add DIR/bin to your PATH to get at the installed commands. If the GOBIN environment variable is set, commands are installed to the directory it names instead of DIR/bin.

Here's an example directory layout:


            bar/               (go code in package bar)
            quux/              (go code in package main)
        quux                   (installed command)
                bar.a          (installed package object)

Go searches each directory listed in GOPATH to find source code, but new packages are always downloaded into the first directory in the list.

Import path syntax

An import path (see 'go help packages') denotes a package stored in the local file system. In general, an import path denotes either a standard package (such as "unicode/utf8") or a package found in one of the work spaces (see 'go help gopath').

Relative import paths

An import path beginning with ./ or ../ is called a relative path. The toolchain supports relative import paths as a shortcut in two ways.

First, a relative path can be used as a shorthand on the command line. If you are working in the directory containing the code imported as "unicode" and want to run the tests for "unicode/utf8", you can type "go test ./utf8" instead of needing to specify the full path. Similarly, in the reverse situation, "go test .." will test "unicode" from the "unicode/utf8" directory. Relative patterns are also allowed, like "go test ./..." to test all subdirectories. See 'go help packages' for details on the pattern syntax.

Second, if you are compiling a Go program not in a work space, you can use a relative path in an import statement in that program to refer to nearby code also not in a work space. This makes it easy to experiment with small multipackage programs outside of the usual work spaces, but such programs cannot be installed with "go install" (there is no work space in which to install them), so they are rebuilt from scratch each time they are built. To avoid ambiguity, Go programs cannot use relative import paths within a work space.

Remote import paths

Certain import paths also describe how to obtain the source code for the package using a revision control system.

A few common code hosting sites have special syntax:

Bitbucket (Git, Mercurial)

	import "bitbucket.org/user/project"
	import "bitbucket.org/user/project/sub/directory"

GitHub (Git)

	import "github.com/user/project"
	import "github.com/user/project/sub/directory"

Google Code Project Hosting (Git, Mercurial, Subversion)

	import "code.google.com/p/project"
	import "code.google.com/p/project/sub/directory"

	import "code.google.com/p/project.subrepository"
	import "code.google.com/p/project.subrepository/sub/directory"

Launchpad (Bazaar)

	import "launchpad.net/project"
	import "launchpad.net/project/series"
	import "launchpad.net/project/series/sub/directory"

	import "launchpad.net/~user/project/branch"
	import "launchpad.net/~user/project/branch/sub/directory"

IBM DevOps Services (Git)

	import "hub.jazz.net/git/user/project"
	import "hub.jazz.net/git/user/project/sub/directory"

For code hosted on other servers, import paths may either be qualified with the version control type, or the go tool can dynamically fetch the import path over https/http and discover where the code resides from a <meta> tag in the HTML.

To declare the code location, an import path of the form


specifies the given repository, with or without the .vcs suffix, using the named version control system, and then the path inside that repository. The supported version control systems are:

Bazaar      .bzr
Git         .git
Mercurial   .hg
Subversion  .svn

For example,

import "example.org/user/foo.hg"

denotes the root directory of the Mercurial repository at example.org/user/foo or foo.hg, and

import "example.org/repo.git/foo/bar"

denotes the foo/bar directory of the Git repository at example.org/repo or repo.git.

When a version control system supports multiple protocols, each is tried in turn when downloading. For example, a Git download tries git://, then https://, then http://.

If the import path is not a known code hosting site and also lacks a version control qualifier, the go tool attempts to fetch the import over https/http and looks for a <meta> tag in the document's HTML <head>.

The meta tag has the form:

<meta name="go-import" content="import-prefix vcs repo-root">

The import-prefix is the import path corresponding to the repository root. It must be a prefix or an exact match of the package being fetched with "go get". If it's not an exact match, another http request is made at the prefix to verify the <meta> tags match.

The vcs is one of "git", "hg", "svn", etc,

The repo-root is the root of the version control system containing a scheme and not containing a .vcs qualifier.

For example,

import "example.org/pkg/foo"

will result in the following request(s):

https://example.org/pkg/foo?go-get=1 (preferred)
http://example.org/pkg/foo?go-get=1  (fallback)

If that page contains the meta tag

<meta name="go-import" content="example.org git https://code.org/r/p/exproj">

the go tool will verify that https://example.org/?go-get=1 contains the same meta tag and then git clone https://code.org/r/p/exproj into GOPATH/src/example.org.

New downloaded packages are written to the first directory listed in the GOPATH environment variable (see 'go help gopath').

The go command attempts to download the version of the package appropriate for the Go release being used. Run 'go help install' for more.

Description of package lists

Many commands apply to a set of packages:

go action [packages]

Usually, [packages] is a list of import paths.

An import path that is a rooted path or that begins with a . or .. element is interpreted as a file system path and denotes the package in that directory.

Otherwise, the import path P denotes the package found in the directory DIR/src/P for some DIR listed in the GOPATH environment variable (see 'go help gopath').

If no import paths are given, the action applies to the package in the current directory.

There are three reserved names for paths that should not be used for packages to be built with the go tool:

- "main" denotes the top-level package in a stand-alone executable.

- "all" expands to all package directories found in all the GOPATH trees. For example, 'go list all' lists all the packages on the local system.

- "std" is like all but expands to just the packages in the standard Go library.

An import path is a pattern if it includes one or more "..." wildcards, each of which can match any string, including the empty string and strings containing slashes. Such a pattern expands to all package directories found in the GOPATH trees with names matching the patterns. As a special case, x/... matches x as well as x's subdirectories. For example, net/... expands to net and packages in its subdirectories.

An import path can also name a package to be downloaded from a remote repository. Run 'go help importpath' for details.

Every package in a program must have a unique import path. By convention, this is arranged by starting each path with a unique prefix that belongs to you. For example, paths used internally at Google all begin with 'google', and paths denoting remote repositories begin with the path to the code, such as 'code.google.com/p/project'.

As a special case, if the package list is a list of .go files from a single directory, the command is applied to a single synthesized package made up of exactly those files, ignoring any build constraints in those files and ignoring any other files in the directory.

Directory and file names that begin with "." or "_" are ignored by the go tool, as are directories named "testdata".

Description of testing flags

The 'go test' command takes both flags that apply to 'go test' itself and flags that apply to the resulting test binary.

Several of the flags control profiling and write an execution profile suitable for "go tool pprof"; run "go tool pprof help" for more information. The --alloc_space, --alloc_objects, and --show_bytes options of pprof control how the information is presented.

The following flags are recognized by the 'go test' command and control the execution of any test:

-bench regexp
    Run benchmarks matching the regular expression.
    By default, no benchmarks run. To run all benchmarks,
    use '-bench .' or '-bench=.'.

    Print memory allocation statistics for benchmarks.

-benchtime t
    Run enough iterations of each benchmark to take t, specified
    as a time.Duration (for example, -benchtime 1h30s).
    The default is 1 second (1s).

-blockprofile block.out
    Write a goroutine blocking profile to the specified file
    when all tests are complete.
    Writes test binary as -c would.

-blockprofilerate n
    Control the detail provided in goroutine blocking profiles by
    calling runtime.SetBlockProfileRate with n.
    See 'godoc runtime SetBlockProfileRate'.
    The profiler aims to sample, on average, one blocking event every
    n nanoseconds the program spends blocked.  By default,
    if -test.blockprofile is set without this flag, all blocking events
    are recorded, equivalent to -test.blockprofilerate=1.

    Enable coverage analysis.

-covermode set,count,atomic
    Set the mode for coverage analysis for the package[s]
    being tested. The default is "set" unless -race is enabled,
    in which case it is "atomic".
    The values:
	set: bool: does this statement run?
	count: int: how many times does this statement run?
	atomic: int: count, but correct in multithreaded tests;
		significantly more expensive.
    Sets -cover.

-coverpkg pkg1,pkg2,pkg3
    Apply coverage analysis in each test to the given list of packages.
    The default is for each test to analyze only the package being tested.
    Packages are specified as import paths.
    Sets -cover.

-coverprofile cover.out
    Write a coverage profile to the file after all tests have passed.
    Sets -cover.

-cpu 1,2,4
    Specify a list of GOMAXPROCS values for which the tests or
    benchmarks should be executed.  The default is the current value

-cpuprofile cpu.out
    Write a CPU profile to the specified file before exiting.
    Writes test binary as -c would.

-memprofile mem.out
    Write a memory profile to the file after all tests have passed.
    Writes test binary as -c would.

-memprofilerate n
    Enable more precise (and expensive) memory profiles by setting
    runtime.MemProfileRate.  See 'godoc runtime MemProfileRate'.
    To profile all memory allocations, use -test.memprofilerate=1
    and pass --alloc_space flag to the pprof tool.

-outputdir directory
    Place output files from profiling in the specified directory,
    by default the directory in which "go test" is running.

-parallel n
    Allow parallel execution of test functions that call t.Parallel.
    The value of this flag is the maximum number of tests to run
    simultaneously; by default, it is set to the value of GOMAXPROCS.

-run regexp
    Run only those tests and examples matching the regular

    Tell long-running tests to shorten their run time.
    It is off by default but set during all.bash so that installing
    the Go tree can run a sanity check but not spend time running
    exhaustive tests.

-timeout t
    If a test runs longer than t, panic.

    Verbose output: log all tests as they are run. Also print all
    text from Log and Logf calls even if the test succeeds.

The test binary, called pkg.test where pkg is the name of the directory containing the package sources, can be invoked directly after building it with 'go test -c'. When invoking the test binary directly, each of the standard flag names must be prefixed with 'test.', as in -test.run=TestMyFunc or -test.v.

When running 'go test', flags not listed above are passed through unaltered. For instance, the command

go test -x -v -cpuprofile=prof.out -dir=testdata -update

will compile the test binary and then run it as

pkg.test -test.v -test.cpuprofile=prof.out -dir=testdata -update

The test flags that generate profiles (other than for coverage) also leave the test binary in pkg.test for use when analyzing the profiles.

Flags not recognized by 'go test' must be placed after any specified packages.

Description of testing functions

The 'go test' command expects to find test, benchmark, and example functions in the "*_test.go" files corresponding to the package under test.

A test function is one named TestXXX (where XXX is any alphanumeric string not starting with a lower case letter) and should have the signature,

func TestXXX(t *testing.T) { ... }

A benchmark function is one named BenchmarkXXX and should have the signature,

func BenchmarkXXX(b *testing.B) { ... }

An example function is similar to a test function but, instead of using *testing.T to report success or failure, prints output to os.Stdout. That output is compared against the function's "Output:" comment, which must be the last comment in the function body (see example below). An example with no such comment, or with no text after "Output:" is compiled but not executed.

Godoc displays the body of ExampleXXX to demonstrate the use of the function, constant, or variable XXX. An example of a method M with receiver type T or *T is named ExampleT_M. There may be multiple examples for a given function, constant, or variable, distinguished by a trailing _xxx, where xxx is a suffix not beginning with an upper case letter.

Here is an example of an example:

func ExamplePrintln() {
	Println("The output of\nthis example.")
	// Output: The output of
	// this example.

The entire test file is presented as the example when it contains a single example function, at least one other function, type, variable, or constant declaration, and no test or benchmark functions.

See the documentation of the testing package for more information.

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