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Documentation
¶
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:
buildconstraint build constraints 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.
Print Go environment information ¶
Usage:
go env [-json] [-u] [-w] [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.
The -json flag prints the environment in JSON format instead of as a shell script.
The -u flag requires one or more arguments and unsets the default setting for the named environment variables, if one has been set with 'go env -w'.
The -w flag requires one or more arguments of the form NAME=VALUE and changes the default settings of the named environment variables to the given values.
For more about environment variables, see 'go help environment'.
Update packages to use new APIs ¶
Usage:
go fix [packages]
Fix runs the Go fix command on the packages named by the import paths.
For more about fix, see 'go doc cmd/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.
Gofmt (reformat) package sources ¶
Usage:
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 'go doc cmd/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.
The -mod flag's value sets which module download mode to use: readonly or vendor. See 'go help modules' for more.
To run gofmt with specific options, run gofmt itself.
See also: go fix, go vet.
Generate Go files by processing source ¶
Usage:
go generate [-run regexp] [-n] [-v] [-x] [build flags] [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.
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.
To convey to humans and machine tools that code is generated, generated source should have a line that matches the following regular expression (in Go syntax):
^// Code generated .* DO NOT EDIT\.$
The line may appear anywhere in the file, but is typically placed near the beginning so it is easy to find.
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:
$GOARCH The execution architecture (arm, amd64, etc.) $GOOS The execution operating system (linux, windows, etc.) $GOFILE The base name of the file. $GOLINE The line number of the directive in the source file. $GOPACKAGE The name of the package of the file containing the directive. $DOLLAR A dollar sign.
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 foo go tool foo
specifies that the command "foo" represents the generator "go tool foo".
Generate processes packages in the order given on the command line, one at a time. If the command line lists .go files from a single directory, 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. The go generate tool also sets the build tag "generate" so that files may be examined by go generate but ignored during build.
For packages with invalid code, generate processes only source files with a valid package clause.
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:
-run="" if non-empty, specifies a regular expression to select directives whose full original source text (excluding any trailing spaces and final newline) matches the expression.
It also accepts the standard build flags including -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 build flags, see 'go help build'.
For more about specifying packages, see 'go help packages'.
Add dependencies to current module and install them ¶
Usage:
go get [-d] [-t] [-u] [-v] [-insecure] [build flags] [packages]
Get resolves and adds dependencies to the current development module and then builds and installs them.
The first step is to resolve which dependencies to add.
For each named package or package pattern, get must decide which version of the corresponding module to use. By default, get looks up the latest tagged release version, such as v0.4.5 or v1.2.3. If there are no tagged release versions, get looks up the latest tagged pre-release version, such as v0.0.1-pre1. If there are no tagged versions at all, get looks up the latest known commit. If the module is not already required at a later version (for example, a pre-release newer than the latest release), get will use the version it looked up. Otherwise, get will use the currently required version.
This default version selection can be overridden by adding an @version suffix to the package argument, as in 'go get golang.org/x/text@v0.3.0'. The version may be a prefix: @v1 denotes the latest available version starting with v1. See 'go help modules' under the heading 'Module queries' for the full query syntax.
For modules stored in source control repositories, the version suffix can also be a commit hash, branch identifier, or other syntax known to the source control system, as in 'go get golang.org/x/text@master'. Note that branches with names that overlap with other module query syntax cannot be selected explicitly. For example, the suffix @v2 means the latest version starting with v2, not the branch named v2.
If a module under consideration is already a dependency of the current development module, then get will update the required version. Specifying a version earlier than the current required version is valid and downgrades the dependency. The version suffix @none indicates that the dependency should be removed entirely, downgrading or removing modules depending on it as needed.
The version suffix @latest explicitly requests the latest minor release of the module named by the given path. The suffix @upgrade is like @latest but will not downgrade a module if it is already required at a revision or pre-release version newer than the latest released version. The suffix @patch requests the latest patch release: the latest released version with the same major and minor version numbers as the currently required version. Like @upgrade, @patch will not downgrade a module already required at a newer version. If the path is not already required, @upgrade and @patch are equivalent to @latest.
Although get defaults to using the latest version of the module containing a named package, it does not use the latest version of that module's dependencies. Instead it prefers to use the specific dependency versions requested by that module. For example, if the latest A requires module B v1.2.3, while B v1.2.4 and v1.3.1 are also available, then 'go get A' will use the latest A but then use B v1.2.3, as requested by A. (If there are competing requirements for a particular module, then 'go get' resolves those requirements by taking the maximum requested version.)
The -t flag instructs get to consider modules needed to build tests of packages specified on the command line.
The -u flag instructs get to update modules providing dependencies of packages named on the command line to use newer minor or patch releases when available. Continuing the previous example, 'go get -u A' will use the latest A with B v1.3.1 (not B v1.2.3). If B requires module C, but C does not provide any packages needed to build packages in A (not including tests), then C will not be updated.
The -u=patch flag (not -u patch) also instructs get to update dependencies, but changes the default to select patch releases. Continuing the previous example, 'go get -u=patch A@latest' will use the latest A with B v1.2.4 (not B v1.2.3), while 'go get -u=patch A' will use a patch release of A instead.
When the -t and -u flags are used together, get will update test dependencies as well.
In general, adding a new dependency may require upgrading existing dependencies to keep a working build, and 'go get' does this automatically. Similarly, downgrading one dependency may require downgrading other dependencies, and 'go get' does this automatically as well.
The -insecure flag permits fetching from repositories and resolving custom domains using insecure schemes such as HTTP. Use with caution. The GOINSECURE environment variable is usually a better alternative, since it provides control over which modules may be retrieved using an insecure scheme. See 'go help environment' for details.
The second step is to download (if needed), build, and install the named packages.
If an argument names a module but not a package (because there is no Go source code in the module's root directory), then the install step is skipped for that argument, instead of causing a build failure. For example 'go get golang.org/x/perf' succeeds even though there is no code corresponding to that import path.
Note that package patterns are allowed and are expanded after resolving the module versions. For example, 'go get golang.org/x/perf/cmd/...' adds the latest golang.org/x/perf and then installs the commands in that latest version.
The -d flag instructs get to download the source code needed to build the named packages, including downloading necessary dependencies, but not to build and install them.
With no package arguments, 'go get' applies to Go package in the current directory, if any. In particular, 'go get -u' and 'go get -u=patch' update all the dependencies of that package. With no package arguments and also without -u, 'go get' is not much more than 'go install', and 'go get -d' not much more than 'go list'.
For more about modules, see 'go help modules'.
For more about specifying packages, see 'go help packages'.
This text describes the behavior of get using modules to manage source code and dependencies. If instead the go command is running in GOPATH mode, the details of get's flags and effects change, as does 'go help get'. See 'go help modules' and 'go help gopath-get'.
See also: go build, go install, go clean, go mod.
Compile and install packages and dependencies ¶
Usage:
go install [-i] [build flags] [packages]
Install compiles and installs the packages named by the import paths.
Executables are installed in the directory named by the GOBIN environment variable, which defaults to $GOPATH/bin or $HOME/go/bin if the GOPATH environment variable is not set. Executables in $GOROOT are installed in $GOROOT/bin or $GOTOOLDIR instead of $GOBIN.
When module-aware mode is disabled, other packages are installed in the directory $GOPATH/pkg/$GOOS_$GOARCH. When module-aware mode is enabled, other packages are built and cached but not installed.
The -i flag installs the dependencies of the named packages as well.
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 or modules ¶
Usage:
go list [-f format] [-json] [-m] [list flags] [build flags] [packages]
List lists the named packages, one per line. The most commonly-used flags are -f and -json, which control the form of the output printed for each package. Other list flags, documented below, control more specific details.
The default output shows the package import path:
bytes encoding/json github.com/gorilla/mux golang.org/x/net/html
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
Shlib string // the shared library that contains this package (only set when -linkshared)
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?
StaleReason string // explanation for Stale==true
Root string // Go root or Go path dir containing this package
ConflictDir string // this directory shadows Dir in $GOPATH
BinaryOnly bool // binary-only package (no longer supported)
ForTest string // package is only for use in named test
Export string // file containing export data (when using -export)
Module *Module // info about package's containing module, if any (can be nil)
Match []string // command-line patterns matching this package
DepOnly bool // package is only a dependency, not explicitly listed
// Source files
GoFiles []string // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
CgoFiles []string // .go source files that import "C"
CompiledGoFiles []string // .go files presented to compiler (when using -compiled)
IgnoredGoFiles []string // .go source files 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
FFiles []string // .f, .F, .for and .f90 Fortran source files
SFiles []string // .s source files
SwigFiles []string // .swig files
SwigCXXFiles []string // .swigcxx files
SysoFiles []string // .syso object files to add to archive
TestGoFiles []string // _test.go files in package
XTestGoFiles []string // _test.go files outside package
// Cgo directives
CgoCFLAGS []string // cgo: flags for C compiler
CgoCPPFLAGS []string // cgo: flags for C preprocessor
CgoCXXFLAGS []string // cgo: flags for C++ compiler
CgoFFLAGS []string // cgo: flags for Fortran compiler
CgoLDFLAGS []string // cgo: flags for linker
CgoPkgConfig []string // cgo: pkg-config names
// Dependency information
Imports []string // import paths used by this package
ImportMap map[string]string // map from source import to ImportPath (identity entries omitted)
Deps []string // all (recursively) imported dependencies
TestImports []string // imports from TestGoFiles
XTestImports []string // imports from XTestGoFiles
// Error information
Incomplete bool // this package or a dependency has an error
Error *PackageError // error loading package
DepsErrors []*PackageError // errors loading dependencies
}
Packages stored in vendor directories report an ImportPath that includes the path to the vendor directory (for example, "d/vendor/p" instead of "p"), so that the ImportPath uniquely identifies a given copy of a package. The Imports, Deps, TestImports, and XTestImports lists also contain these expanded import paths. See golang.org/s/go15vendor for more about vendoring.
The error information, if any, is
type PackageError struct {
ImportStack []string // shortest path from package named on command line to this one
Pos string // position of error (if present, file:line:col)
Err string // the error itself
}
The module information is a Module struct, defined in the discussion of list -m below.
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 -compiled flag causes list to set CompiledGoFiles to the Go source files presented to the compiler. Typically this means that it repeats the files listed in GoFiles and then also adds the Go code generated by processing CgoFiles and SwigFiles. The Imports list contains the union of all imports from both GoFiles and CompiledGoFiles.
The -deps flag causes list to iterate over not just the named packages but also all their dependencies. It visits them in a depth-first post-order traversal, so that a package is listed only after all its dependencies. Packages not explicitly listed on the command line will have the DepOnly field set to true.
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).
The -export flag causes list to set the Export field to the name of a file containing up-to-date export information for the given package.
The -find flag causes list to identify the named packages but not resolve their dependencies: the Imports and Deps lists will be empty.
The -test flag causes list to report not only the named packages but also their test binaries (for packages with tests), to convey to source code analysis tools exactly how test binaries are constructed. The reported import path for a test binary is the import path of the package followed by a ".test" suffix, as in "math/rand.test". When building a test, it is sometimes necessary to rebuild certain dependencies specially for that test (most commonly the tested package itself). The reported import path of a package recompiled for a particular test binary is followed by a space and the name of the test binary in brackets, as in "math/rand math/rand.test" or "regexp [sort.test]". The ForTest field is also set to the name of the package being tested ("math/rand" or "sort" in the previous examples).
The Dir, Target, Shlib, Root, ConflictDir, and Export file paths are all absolute paths.
By default, the lists GoFiles, CgoFiles, and so on hold names of files in Dir (that is, paths relative to Dir, not absolute paths). The generated files added when using the -compiled and -test flags are absolute paths referring to cached copies of generated Go source files. Although they are Go source files, the paths may not end in ".go".
The -m flag causes list to list modules instead of packages.
When listing modules, the -f flag still specifies a format template applied to a Go struct, but now a Module struct:
type Module struct {
Path string // module path
Version string // module version
Versions []string // available module versions (with -versions)
Replace *Module // replaced by this module
Time *time.Time // time version was created
Update *Module // available update, if any (with -u)
Main bool // is this the main module?
Indirect bool // is this module only an indirect dependency of main module?
Dir string // directory holding files for this module, if any
GoMod string // path to go.mod file used when loading this module, if any
GoVersion string // go version used in module
Error *ModuleError // error loading module
}
type ModuleError struct {
Err string // the error itself
}
The file GoMod refers to may be outside the module directory if the module is in the module cache or if the -modfile flag is used.
The default output is to print the module path and then information about the version and replacement if any. For example, 'go list -m all' might print:
my/main/module golang.org/x/text v0.3.0 => /tmp/text rsc.io/pdf v0.1.1
The Module struct has a String method that formats this line of output, so that the default format is equivalent to -f '{{.String}}'.
Note that when a module has been replaced, its Replace field describes the replacement module, and its Dir field is set to the replacement's source code, if present. (That is, if Replace is non-nil, then Dir is set to Replace.Dir, with no access to the replaced source code.)
The -u flag adds information about available upgrades. When the latest version of a given module is newer than the current one, list -u sets the Module's Update field to information about the newer module. The Module's String method indicates an available upgrade by formatting the newer version in brackets after the current version. For example, 'go list -m -u all' might print:
my/main/module golang.org/x/text v0.3.0 [v0.4.0] => /tmp/text rsc.io/pdf v0.1.1 [v0.1.2]
(For tools, 'go list -m -u -json all' may be more convenient to parse.)
The -versions flag causes list to set the Module's Versions field to a list of all known versions of that module, ordered according to semantic versioning, earliest to latest. The flag also changes the default output format to display the module path followed by the space-separated version list.
The arguments to list -m are interpreted as a list of modules, not packages. The main module is the module containing the current directory. The active modules are the main module and its dependencies. With no arguments, list -m shows the main module. With arguments, list -m shows the modules specified by the arguments. Any of the active modules can be specified by its module path. The special pattern "all" specifies all the active modules, first the main module and then dependencies sorted by module path. A pattern containing "..." specifies the active modules whose module paths match the pattern. A query of the form path@version specifies the result of that query, which is not limited to active modules. See 'go help modules' for more about module queries.
The template function "module" takes a single string argument that must be a module path or query and returns the specified module as a Module struct. If an error occurs, the result will be a Module struct with a non-nil Error field.
For more about build flags, see 'go help build'.
For more about specifying packages, see 'go help packages'.
For more about modules, see 'go help modules'.
Module maintenance ¶
Go mod provides access to operations on modules.
Note that support for modules is built into all the go commands, not just 'go mod'. For example, day-to-day adding, removing, upgrading, and downgrading of dependencies should be done using 'go get'. See 'go help modules' for an overview of module functionality.
Usage:
go mod <command> [arguments]
The commands are:
download download modules to local cache edit edit go.mod from tools or scripts graph print module requirement graph init initialize new module in current directory tidy add missing and remove unused modules vendor make vendored copy of dependencies verify verify dependencies have expected content why explain why packages or modules are needed
Use "go help mod <command>" for more information about a command.
Download modules to local cache ¶
Usage:
go mod download [-x] [-json] [modules]
Download downloads the named modules, which can be module patterns selecting dependencies of the main module or module queries of the form path@version. With no arguments, download applies to all dependencies of the main module (equivalent to 'go mod download all').
The go command will automatically download modules as needed during ordinary execution. The "go mod download" command is useful mainly for pre-filling the local cache or to compute the answers for a Go module proxy.
By default, download writes nothing to standard output. It may print progress messages and errors to standard error.
The -json flag causes download to print a sequence of JSON objects to standard output, describing each downloaded module (or failure), corresponding to this Go struct:
type Module struct {
Path string // module path
Version string // module version
Error string // error loading module
Info string // absolute path to cached .info file
GoMod string // absolute path to cached .mod file
Zip string // absolute path to cached .zip file
Dir string // absolute path to cached source root directory
Sum string // checksum for path, version (as in go.sum)
GoModSum string // checksum for go.mod (as in go.sum)
}
The -x flag causes download to print the commands download executes.
See 'go help modules' for more about module queries.
Edit go.mod from tools or scripts ¶
Usage:
go mod edit [editing flags] [go.mod]
Edit provides a command-line interface for editing go.mod, for use primarily by tools or scripts. It reads only go.mod; it does not look up information about the modules involved. By default, edit reads and writes the go.mod file of the main module, but a different target file can be specified after the editing flags.
The editing flags specify a sequence of editing operations.
The -fmt flag reformats the go.mod file without making other changes. This reformatting is also implied by any other modifications that use or rewrite the go.mod file. The only time this flag is needed is if no other flags are specified, as in 'go mod edit -fmt'.
The -module flag changes the module's path (the go.mod file's module line).
The -require=path@version and -droprequire=path flags add and drop a requirement on the given module path and version. Note that -require overrides any existing requirements on path. These flags are mainly for tools that understand the module graph. Users should prefer 'go get path@version' or 'go get path@none', which make other go.mod adjustments as needed to satisfy constraints imposed by other modules.
The -exclude=path@version and -dropexclude=path@version flags add and drop an exclusion for the given module path and version. Note that -exclude=path@version is a no-op if that exclusion already exists.
The -replace=old[@v]=new[@v] flag adds a replacement of the given module path and version pair. If the @v in old@v is omitted, a replacement without a version on the left side is added, which applies to all versions of the old module path. If the @v in new@v is omitted, the new path should be a local module root directory, not a module path. Note that -replace overrides any redundant replacements for old[@v], so omitting @v will drop existing replacements for specific versions.
The -dropreplace=old[@v] flag drops a replacement of the given module path and version pair. If the @v is omitted, a replacement without a version on the left side is dropped.
The -require, -droprequire, -exclude, -dropexclude, -replace, and -dropreplace editing flags may be repeated, and the changes are applied in the order given.
The -go=version flag sets the expected Go language version.
The -print flag prints the final go.mod in its text format instead of writing it back to go.mod.
The -json flag prints the final go.mod file in JSON format instead of writing it back to go.mod. The JSON output corresponds to these Go types:
type Module struct {
Path string
Version string
}
type GoMod struct {
Module Module
Go string
Require []Require
Exclude []Module
Replace []Replace
}
type Require struct {
Path string
Version string
Indirect bool
}
type Replace struct {
Old Module
New Module
}
Note that this only describes the go.mod file itself, not other modules referred to indirectly. For the full set of modules available to a build, use 'go list -m -json all'.
For example, a tool can obtain the go.mod as a data structure by parsing the output of 'go mod edit -json' and can then make changes by invoking 'go mod edit' with -require, -exclude, and so on.