Affected by 
Documentation
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Overview ¶
Go is a tool for managing Go source code.
Usage:
go <command> [arguments]
The commands are:
bug start a bug report build compile packages and dependencies clean remove object files and cached files doc show documentation for package or symbol env print Go environment information fix update packages to use new APIs fmt gofmt (reformat) package sources generate generate Go files by processing source get add dependencies to current module and install them install compile and install packages and dependencies list list packages or modules mod module maintenance run compile and run Go program test test packages tool run specified go tool version print Go version vet report likely mistakes in packages
Use "go help <command>" for more information about a command.
Additional help topics:
buildmode build modes c calling between Go and C cache build and test caching environment environment variables filetype file types go.mod the go.mod file gopath GOPATH environment variable gopath-get legacy GOPATH go get goproxy module proxy protocol importpath import path syntax modules modules, module versions, and more module-get module-aware go get module-auth module authentication using go.sum module-private module configuration for non-public modules packages package lists and patterns testflag testing flags testfunc testing functions
Use "go help <topic>" for more information about that topic.
Start a bug report ¶
Usage:
go bug
Bug opens the default browser and starts a new bug report. The report includes useful system information.
Compile packages and dependencies ¶
Usage:
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 to build are a list of .go files from a single directory, build treats them as a list of source files specifying a single package.
When compiling packages, build ignores files that end in '_test.go'.
When compiling a single main package, build writes the resulting executable to an output file named after the first source file ('go build ed.go rx.go' writes 'ed' or 'ed.exe') or the source code directory ('go build unix/sam' writes 'sam' or 'sam.exe'). The '.exe' suffix is added when writing a Windows executable.
When compiling multiple packages or a single non-main package, build compiles the packages but discards the resulting object, serving only as a check that the packages can be built.
The -o flag forces build to write the resulting executable or object to the named output file or directory, instead of the default behavior described in the last two paragraphs. If the named output is a directory that exists, then any resulting executables will be written to that 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:
-a force rebuilding of packages that are already up-to-date. -n print the commands but do not run them. -p n the number of programs, such as build commands or test binaries, that can be run in parallel. The default is the number of CPUs available. -race enable data race detection. Supported only on linux/amd64, freebsd/amd64, darwin/amd64, windows/amd64, linux/ppc64le and linux/arm64 (only for 48-bit VMA). -msan enable interoperation with memory sanitizer. Supported only on linux/amd64, linux/arm64 and only with Clang/LLVM as the host C compiler. On linux/arm64, pie build mode will be used. -v print the names of packages as they are compiled. -work print the name of the temporary work directory and do not delete it when exiting. -x print the commands. -asmflags '[pattern=]arg list' arguments to pass on each go tool asm invocation. -buildmode mode build mode to use. See 'go help buildmode' for more. -compiler name name of compiler to use, as in runtime.Compiler (gccgo or gc). -gccgoflags '[pattern=]arg list' arguments to pass on each gccgo compiler/linker invocation. -gcflags '[pattern=]arg list' arguments to pass on each go tool compile 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. Likewise for the -msan flag. Using a -buildmode option that requires non-default compile flags has a similar effect. -ldflags '[pattern=]arg list' arguments to pass on each go tool link invocation. -linkshared build code that will be linked against shared libraries previously created with -buildmode=shared. -mod mode module download mode to use: readonly, vendor, or mod. See 'go help modules' for more. -modcacherw leave newly-created directories in the module cache read-write instead of making them read-only. -modfile file in module aware mode, read (and possibly write) an alternate go.mod file instead of the one in the module root directory. A file named "go.mod" must still be present in order to determine the module root directory, but it is not accessed. When -modfile is specified, an alternate go.sum file is also used: its path is derived from the -modfile flag by trimming the ".mod" extension and appending ".sum". -pkgdir dir install and load all packages from dir instead of the usual locations. For example, when building with a non-standard configuration, use -pkgdir to keep generated packages in a separate location. -tags tag,list a comma-separated 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. (Earlier versions of Go used a space-separated list, and that form is deprecated but still recognized.) -trimpath remove all file system paths from the resulting executable. Instead of absolute file system paths, the recorded file names will begin with either "go" (for the standard library), or a module path@version (when using modules), or a plain import path (when using GOPATH). -toolexec 'cmd args' a program to use to invoke toolchain programs like vet and asm. For example, instead of running asm, the go command will run 'cmd args /path/to/asm <arguments for asm>'.
The -asmflags, -gccgoflags, -gcflags, and -ldflags flags accept a space-separated list of arguments to pass to an underlying tool during the build. To embed spaces in an element in the list, surround it with either single or double quotes. The argument list may be preceded by a package pattern and an equal sign, which restricts the use of that argument list to the building of packages matching that pattern (see 'go help packages' for a description of package patterns). Without a pattern, the argument list applies only to the packages named on the command line. The flags may be repeated with different patterns in order to specify different arguments for different sets of packages. If a package matches patterns given in multiple flags, the latest match on the command line wins. For example, 'go build -gcflags=-S fmt' prints the disassembly only for package fmt, while 'go build -gcflags=all=-S fmt' prints the disassembly for fmt and all its dependencies.
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'.
Note: Build adheres to certain conventions such as those described by 'go help gopath'. Not all projects can follow these conventions, however. Installations that have their own conventions or that use a separate software build system may choose to use lower-level invocations such as 'go tool compile' and 'go tool link' to avoid some of the overheads and design decisions of the build tool.
See also: go install, go get, go clean.
Remove object files and cached files ¶
Usage:
go clean [clean flags] [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.
If a package argument is given or the -i or -r flag is set, 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.
The -cache flag causes clean to remove the entire go build cache.
The -testcache flag causes clean to expire all test results in the go build cache.
The -modcache flag causes clean to remove the entire module download cache, including unpacked source code of versioned dependencies.
For more about build flags, see 'go help build'.
For more about specifying packages, see 'go help packages'.
Show documentation for package or symbol ¶
Usage:
go doc [-u] [-c] [package|[package.]symbol[.methodOrField]]
Doc prints the documentation comments associated with the item identified by its arguments (a package, const, func, type, var, method, or struct field) followed by a one-line summary of each of the first-level items "under" that item (package-level declarations for a package, methods for a type, etc.).
Doc accepts zero, one, or two arguments.
Given no arguments, that is, when run as
go doc
it prints the package documentation for the package in the current directory. If the package is a command (package main), the exported symbols of the package are elided from the presentation unless the -cmd flag is provided.
When run with one argument, the argument is treated as a Go-syntax-like representation of the item to be documented. What the argument selects depends on what is installed in GOROOT and GOPATH, as well as the form of the argument, which is schematically one of these:
go doc <pkg> go doc <sym>[.<methodOrField>] go doc [<pkg>.]<sym>[.<methodOrField>] go doc [<pkg>.][<sym>.]<methodOrField>
The first item in this list matched by the argument is the one whose documentation is printed. (See the examples below.) However, if the argument starts with a capital letter it is assumed to identify a symbol or method in the current directory.
For packages, the order of scanning is determined lexically in breadth-first order. That is, the package presented is the one that matches the search and is nearest the root and lexically first at its level of the hierarchy. The GOROOT tree is always scanned in its entirety before GOPATH.
If there is no package specified or matched, the package in the current directory is selected, so "go doc Foo" shows the documentation for symbol Foo in the current package.
The package path must be either a qualified path or a proper suffix of a path. The go tool's usual package mechanism does not apply: package path elements like . and ... are not implemented by go doc.
When run with two arguments, the first must be a full package path (not just a suffix), and the second is a symbol, or symbol with method or struct field. This is similar to the syntax accepted by godoc:
go doc <pkg> <sym>[.<methodOrField>]
In all forms, when matching symbols, lower-case letters in the argument match either case but upper-case letters match exactly. This means that there may be multiple matches of a lower-case argument in a package if different symbols have different cases. If this occurs, documentation for all matches is printed.
Examples:
go doc Show documentation for current package. go doc Foo Show documentation for Foo in the current package. (Foo starts with a capital letter so it cannot match a package path.) go doc encoding/json Show documentation for the encoding/json package. go doc json Shorthand for encoding/json. go doc json.Number (or go doc json.number) Show documentation and method summary for json.Number. go doc json.Number.Int64 (or go doc json.number.int64) Show documentation for json.Number's Int64 method. go doc cmd/doc Show package docs for the doc command. go doc -cmd cmd/doc Show package docs and exported symbols within the doc command. go doc template.new Show documentation for html/template's New function. (html/template is lexically before text/template) go doc text/template.new # One argument Show documentation for text/template's New function. go doc text/template new # Two arguments Show documentation for text/template's New function. At least in the current tree, these invocations all print the documentation for json.Decoder's Decode method: go doc json.Decoder.Decode go doc json.decoder.decode go doc json.decode cd go/src/encoding/json; go doc decode
Flags:
-all Show all the documentation for the package. -c Respect case when matching symbols. -cmd Treat a command (package main) like a regular package. Otherwise package main's exported symbols are hidden when showing the package's top-level documentation. -short One-line representation for each symbol. -src Show the full source code for the symbol. This will display the full Go source of its declaration and definition, such as a function definition (including the body), type declaration or enclosing const block. The output may therefore include unexported details. -u Show documentation for unexported as well as exported symbols, methods, and fields.