In this quick lab, you will experience the most important Go Modules concepts:<\/p>\n\n\n\n
import<\/code>\u00a0\u2014 use a package in Go source code<\/li>\n\n\n\nrequire<\/code>\u00a0\u2014 record the module\/version in\u00a0go.mod<\/code><\/li>\n\n\n\n- Module cache \u2014 find where Go downloaded the dependency<\/li>\n\n\n\n
go.sum<\/code>\u00a0\u2014 verify downloaded module content<\/li>\n\n\n\n- Version management \u2014 inspect and pin a dependency version<\/li>\n\n\n\n
replace<\/code>\u00a0\u2014 understand how a module can be redirected to another location<\/li>\n\n\n\n- Essential Go module commands<\/li>\n<\/ul>\n\n\n\n
Estimated time:<\/strong> 15 minutes<\/p>\n\n\n\n
\n\n\n\n1. Check Go and Create the Module \u2014 2 minutes<\/h2>\n\n\n\n
Check Go:<\/p>\n\n\n\n
go version\n<\/code><\/pre>\n\n\n\nCreate the lab project:<\/p>\n\n\n\n
mkdir go-modules-lab\ncd go-modules-lab\ngo mod init example.com\/go-modules-lab\n<\/code><\/pre>\n\n\n\nInspect the generated file:<\/p>\n\n\n\n
cat go.mod\n<\/code><\/pre>\n\n\n\nExample:<\/p>\n\n\n\n
module example.com\/go-modules-lab\n\ngo 1.24\n<\/code><\/pre>\n\n\n\n\nYour Go version may be different.<\/p>\n<\/blockquote>\n\n\n\n
What happened?<\/h3>\n\n\n\n
go mod init<\/code> created go.mod<\/code>, which identifies this project as a Go module.<\/p>\n\n\n\n
\n\n\n\n2. Import an External Package \u2014 3 minutes<\/h2>\n\n\n\n
Create main.go<\/code>:<\/p>\n\n\n\npackage main\n\nimport (\n \"fmt\"\n\n \"github.com\/google\/uuid\"\n)\n\nfunc main() {\n id := uuid.New()\n fmt.Println(\"Generated ID:\", id)\n}\n<\/code><\/pre>\n\n\n\nNotice this line:<\/p>\n\n\n\n
import \"github.com\/google\/uuid\"\n<\/code><\/pre>\n\n\n\nAn import<\/strong> appears in Go source code. It tells the compiler that this package is used by the program.<\/p>\n\n\n\nNow synchronize dependencies:<\/p>\n\n\n\n
go mod tidy\n<\/code><\/pre>\n\n\n\nRun the application:<\/p>\n\n\n\n
go run .\n<\/code><\/pre>\n\n\n\nExample output:<\/p>\n\n\n\n
Generated ID: 550e8400-e29b-41d4-a716-446655440000\n<\/code><\/pre>\n\n\n\nThe UUID will be different each time.<\/p>\n\n\n\n
\n\n\n\n3. See How import<\/code> Becomes require<\/code> \u2014 2 minutes<\/h2>\n\n\n\nInspect go.mod<\/code>:<\/p>\n\n\n\ncat go.mod\n<\/code><\/pre>\n\n\n\nYou should see an entry similar to:<\/p>\n\n\n\n
module example.com\/go-modules-lab\n\ngo 1.24\n\nrequire github.com\/google\/uuid v1.6.0\n<\/code><\/pre>\n\n\n\nImport vs. Require<\/h3>\n\n\n\nItem<\/th> Location<\/th> Meaning<\/th><\/tr><\/thead> import<\/code><\/td>.go<\/code> source file<\/td>This code uses a package<\/td><\/tr> require<\/code><\/td>go.mod<\/code><\/td>This module needs a particular module version<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nIn this example:<\/p>\n\n\n\n
import \"github.com\/google\/uuid\"\n<\/code><\/pre>\n\n\n\ncauses Go tooling to record the providing module in go.mod<\/code>:<\/p>\n\n\n\nrequire github.com\/google\/uuid v1.6.0\n<\/code><\/pre>\n\n\n\nUsually, let Go commands such as go get<\/code> and go mod tidy<\/code> manage dependency requirements instead of manually editing versions.<\/p>\n\n\n\n
\n\n\n\n4. Find Where Go Downloaded the Module \u2014 2 minutes<\/h2>\n\n\n\n
Display the module cache location:<\/p>\n\n\n\n
go env GOMODCACHE\n<\/code><\/pre>\n\n\n\nA common location is similar to:<\/p>\n\n\n\n
\/home\/student\/go\/pkg\/mod\n<\/code><\/pre>\n\n\n\nThe default module cache is normally under:<\/p>\n\n\n\n
$GOPATH\/pkg\/mod\n<\/code><\/pre>\n\n\n\nCheck your GOPATH:<\/p>\n\n\n\n
go env GOPATH\n<\/code><\/pre>\n\n\n\nNow ask Go for the exact directory of the downloaded UUID module:<\/p>\n\n\n\n
go list -m -f '{{.Dir}}' github.com\/google\/uuid\n<\/code><\/pre>\n\n\n\nExample:<\/p>\n\n\n\n
\/home\/student\/go\/pkg\/mod\/github.com\/google\/uuid@v1.6.0\n<\/code><\/pre>\n\n\n\nImportant<\/h3>\n\n\n\n
Do not edit files inside the module cache. Go manages this directory.<\/p>\n\n\n\n
To see how Go is configured to obtain modules, run:<\/p>\n\n\n\n
go env GOPROXY\n<\/code><\/pre>\n\n\n\nYou may see something similar to:<\/p>\n\n\n\n
https://proxy.golang.org,direct\n<\/code><\/pre>\n\n\n\nThe module may therefore be obtained through a configured Go module proxy or directly from its version-control source, depending on the environment and module settings.<\/p>\n\n\n\n
\n\n\n\n5. Inspect go.sum<\/code> and the Dependency Version \u2014 2 minutes<\/h2>\n\n\n\nInspect the checksum file:<\/p>\n\n\n\n
cat go.sum\n<\/code><\/pre>\n\n\n\nYou will see entries similar to:<\/p>\n\n\n\n
github.com\/google\/uuid v1.6.0 h1:...\ngithub.com\/google\/uuid v1.6.0\/go.mod h1:...\n<\/code><\/pre>\n\n\n\ngo.sum<\/code> records cryptographic hashes used by Go to verify module content.<\/p>\n\n\n\nBoth go.mod<\/code> and go.sum<\/code> should normally be committed with your project.<\/p>\n\n\n\nSee modules selected for the build:<\/p>\n\n\n\n
go list -m all\n<\/code><\/pre>\n\n\n\nSee available versions of the UUID module:<\/p>\n\n\n\n
go list -m -versions github.com\/google\/uuid\n<\/code><\/pre>\n\n\n\nPin or change to a specific version:<\/p>\n\n\n\n
go get github.com\/google\/uuid@v1.6.0\n<\/code><\/pre>\n\n\n\nThen synchronize:<\/p>\n\n\n\n
go mod tidy\n<\/code><\/pre>\n\n\n\n
\n\n\n\n6. Understand replace<\/code> \u2014 2 minutes<\/h2>\n\n\n\nA replace<\/code> directive tells Go to use module code from another location instead of the normally resolved module source.<\/p>\n\n\n\nExample go.mod<\/code> syntax:<\/p>\n\n\n\nrequire example.com\/sharedlib v0.0.0\n\nreplace example.com\/sharedlib => ..\/sharedlib\n<\/code><\/pre>\n\n\n\nThis is useful when developing two local modules together.<\/p>\n\n\n\n
The application still imports the original module path:<\/p>\n\n\n\n
import \"example.com\/sharedlib\"\n<\/code><\/pre>\n\n\n\nIt does not<\/strong> change to:<\/p>\n\n\n\nimport \"..\/sharedlib\"\n<\/code><\/pre>\n\n\n\nYou can create a replacement directive with:<\/p>\n\n\n\n
go mod edit -replace=example.com\/sharedlib=..\/sharedlib\n<\/code><\/pre>\n\n\n\nView the result:<\/p>\n\n\n\n
cat go.mod\n<\/code><\/pre>\n\n\n\nRemove the demonstration directive afterward:<\/p>\n\n\n\n
go mod edit -dropreplace=example.com\/sharedlib\n<\/code><\/pre>\n\n\n\n\nA replace<\/code> directive redirects a module; it does not by itself make an unused module a dependency. The module must also be required somewhere in the module graph for the replacement to affect the build.<\/p>\n<\/blockquote>\n\n\n\n
\n\n\n\n7. Essential Go Module Commands \u2014 2 minutes<\/h2>\n\n\n\nCommand<\/th> Purpose<\/th><\/tr><\/thead> go mod init example.com\/app<\/code><\/td>Create a new module<\/td><\/tr> go mod tidy<\/code><\/td>Add missing and remove unused requirements<\/td><\/tr> go get module@version<\/code><\/td>Add, upgrade, or downgrade a dependency<\/td><\/tr> go list -m all<\/code><\/td>List modules in the build list<\/td><\/tr> go list -m -versions module<\/code><\/td>Show known versions of a module<\/td><\/tr> go mod why -m module<\/code><\/td>Explain why a module is needed<\/td><\/tr> go mod graph<\/code><\/td>Show the module dependency graph<\/td><\/tr> go mod download<\/code><\/td>Download modules to the module cache<\/td><\/tr> go mod verify<\/code><\/td>Verify cached module content against recorded hashes<\/td><\/tr> go env GOMODCACHE<\/code><\/td>Show downloaded-module cache location<\/td><\/tr> go env GOPROXY<\/code><\/td>Show module download\/proxy configuration<\/td><\/tr> go clean -modcache<\/code><\/td>Remove the entire downloaded module cache<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nTry these three now:<\/p>\n\n\n\n
go mod why -m github.com\/google\/uuid\ngo mod verify\ngo list -m all\n<\/code><\/pre>\n\n\n\n
\n\n\n\nFinal Mental Model<\/h1>\n\n\n\nmain.go\n |\n | import \"github.com\/google\/uuid\"\n v\ngo mod tidy \/ go get\n |\n +----> go.mod\n | require github.com\/google\/uuid v1.6.0\n |\n +----> go.sum\n | dependency checksums\n |\n +----> GOMODCACHE\n downloaded module source\n<\/code><\/pre>\n\n\n\nWith a replacement:<\/p>\n\n\n\n
import example.com\/sharedlib\n |\n v\nrequire example.com\/sharedlib ...\n |\n v\nreplace example.com\/sharedlib => ..\/sharedlib\n |\n v\n local module source\n<\/code><\/pre>\n\n\n\n
\n\n\n\nFinal Check<\/h2>\n\n\n\n
Your project should contain:<\/p>\n\n\n\n
go-modules-lab\/\n\u251c\u2500\u2500 go.mod\n\u251c\u2500\u2500 go.sum\n\u2514\u2500\u2500 main.go\n<\/code><\/pre>\n\n\n\nRun:<\/p>\n\n\n\n
go mod tidy\ngo mod verify\ngo run .\n<\/code><\/pre>\n\n\n\nIf the application runs successfully, the lab is complete.<\/p>\n\n\n\n
What You Experienced<\/h2>\n\n\n\n
You now understand the core dependency flow:<\/p>\n\n\n\n
IMPORT -> package used by source code\nREQUIRE -> module\/version recorded in go.mod\nDOWNLOAD -> module stored in GOMODCACHE\nGO.SUM -> verifies downloaded content\nREPLACE -> redirects a module to another source\/location\n<\/code><\/pre>\n\n\n\nLab complete.<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"Goal In this quick lab, you will experience the most important Go Modules concepts: Estimated time: 15 minutes 1. Check Go and Create the Module \u2014 2 minutes… <\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1118","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/posts\/1118","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/comments?post=1118"}],"version-history":[{"count":1,"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/posts\/1118\/revisions"}],"predecessor-version":[{"id":1119,"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/posts\/1118\/revisions\/1119"}],"wp:attachment":[{"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/media?parent=1118"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/categories?post=1118"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.devopsschool.com\/tutorials\/wp-json\/wp\/v2\/tags?post=1118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}