{"id":597,"date":"2022-04-28T13:26:00","date_gmt":"2022-04-28T13:26:00","guid":{"rendered":"https:\/\/andrejacobs.org\/?p=597"},"modified":"2022-05-27T15:53:03","modified_gmt":"2022-05-27T15:53:03","slug":"learning-go-day-8","status":"publish","type":"post","link":"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-8\/","title":{"rendered":"Learning Go &#8211; Day 8"},"content":{"rendered":"\n<p class=\"has-small-font-size\">Featured image by&nbsp;<a href=\"https:\/\/github.com\/egonelbre\/gophers\" target=\"_blank\" rel=\"noreferrer noopener\">Egon Elbre<\/a><\/p>\n\n\n\n<div class=\"wp-block-jetpack-markdown\"><h3>Implementing the Stringer interface<\/h3>\n<p>The standard library defines the <code>Stringer<\/code> interface that is used to return a string.<\/p>\n<pre><code class=\"language-go\">type Stringer interface {\n\tString() string\n}\n<\/code><\/pre>\n<ul>\n<li>Implement the Stringer interface on your custom types<\/li>\n<\/ul>\n<pre><code class=\"language-go\">type Person struct {\n\tName string\n}\n\n\/\/ Implementation for Stringer\nfunc (p Person) String() string {\n\treturn &quot;My name is &quot; + p.Name\n}\n\n\/\/ Your type can now be passed to function that accept Stringer based types\nfmt.Print(person1)\n<\/code><\/pre>\n<h3>Launching other command line applications<\/h3>\n<p>For example using <code>exec.Command()<\/code> you could build the app during a unit-test and run it.<\/p>\n<pre><code class=\"language-go\">import (\n\t&quot;os&quot;\n\t&quot;os\/exec&quot;\n)\n\napp := exec.Command(&quot;go&quot;, &quot;build&quot;, &quot;-o&quot;, &quot;myapp&quot;)\nif err := app.Run(); err != nil {\n\tfmt.Fprintf(os.Stderr, &quot;Building tool myapp failed with error: %s&quot;, err)\n\tos.Exit(42)\n}\n<\/code><\/pre>\n<ul>\n<li>You can bind Stderr to be outputted into Stdout before running the command.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">cmd := exec.Command(&quot;ls&quot;, &quot;-la&quot;)\nout, err := cmd.CombinedOutput()\n\/\/ Convert out to a string for processing\noutString = string(out)\n<\/code><\/pre>\n<ul>\n<li>You can get access to the command\u2019s Stdin pipe and write to it.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">cmdStdIn, err := cmd.StdinPipe()\n\nio.WriteString(cmdStdIn, &quot;Input to be passed to stdin of the process&quot;)\ncmdStdIn.Close()\n\nif err := cmd.Run(); err != nil {\n}\n<\/code><\/pre>\n<ul>\n<li>You can redirect the Stdout or Stderr output to any io.Writer.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">cmd := exec.Command(&quot;ls&quot;, &quot;-la&quot;)\ncmd.Stdout = &amp;someOtherIOWriter\ncmd.Run()\n<\/code><\/pre>\n<ul>\n<li>Change the working directory the command executes in with <code>cmd.Dir = somePath<\/code>.<\/li>\n<li>Set environment variables for the command by setting <code>cmd.Env<\/code> which is defined as <code>Env []string<\/code>. Each string is \u201ckey=value\u201d.<\/li>\n<li>To see if a specific executable can be found in the $PATH variable, use <code>exec.LookPath()<\/code>.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">path, err := exec.LookPath(&quot;git&quot;)\nif err != nil {\n\tlog.Fatal(&quot;git need to be installed&quot;)\n}\nfmt.Printf(&quot;git was found at %s\\n&quot;, path)\n<\/code><\/pre>\n<ul>\n<li>NOTE: There is this package called <code>context<\/code> which among many other things can also be used in combination with <code>exec<\/code> to execute commands with a timeout or to allow to be cancelled etc. See <a href=\"https:\/\/www.digitalocean.com\/community\/tutorials\/how-to-use-contexts-in-go\">this<\/a> for a general guide on how to use context.<\/li>\n<\/ul>\n<h3>Miscellaneous<\/h3>\n<ul>\n<li>Can track date time using the <code>time<\/code> package and the <code>time.Time<\/code> type.<\/li>\n<li>To get the current date time, use <code>time.Now()<\/code> method.<\/li>\n<li>Recall you can return <code>error<\/code> type from your functions\/methods and use <code>fmt.Errorf<\/code> to return a string based error message.<\/li>\n<li>You can use the <code>errors<\/code> package to check for OS errors.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">import &quot;errors&quot;\n\nif errors.Is(err, os.ErrNotExist) {\n...\n}\n<\/code><\/pre>\n<ul>\n<li>The package <code>ioutil<\/code> has been <a href=\"https:\/\/pkg.go.dev\/io\/ioutil\">deprecated<\/a> from Go 1.16. It is replaced with <code>io<\/code> and <code>os<\/code><\/li>\n<li>You can remove files using <code>os.Remove()<\/code>.<\/li>\n<li>Get the current working directory with <code>os.Getwd()<\/code>.<\/li>\n<li>You can read an environment variable using <code>os.Getenv()<\/code>.<\/li>\n<li>You can join strings together using <code>strings.Join(elems []string, sep string) string<\/code>.<\/li>\n<li>You can declare a multiline string using the backticks `<\/li>\n<\/ul>\n<pre><code class=\"language-go\">const multiline = `This is\na multiline\nstring in golang\n`\n<\/code><\/pre>\n<ul>\n<li>To get just the filename from a path.<\/li>\n<\/ul>\n<pre><code class=\"language-go\">import &quot;path\/filepath&quot;\n\nfmt.Println(filepath.Base(&quot;test.txt&quot;)) \/\/ test.txt\nfmt.Println(filepath.Base(&quot;a\/b\/c\/test.txt&quot;)) \/\/ test.txt\n<\/code><\/pre>\n<ul>\n<li>You can build up a buffer and then create a []byte (slice of bytes) using <code>bytes.Buffer<\/code><\/li>\n<\/ul>\n<pre><code class=\"language-go\">func makeBytes() []byte {\n\tvar buffer bytes.Buffer\n\n\tbuffer.WriteString(&quot;The quick brown fox &quot;)\n\tbuffer.WriteString(&quot;jumped over the lazy dog&quot;)\n\n\treturn buffer.Bytes()\n}\n\nfmt.Println(makeBytes())\n\/\/ [84 104 101 32 113 117 105 99 107 32 98 114 111 119 ...\nfmt.Println(string(makeBytes()))\n\/\/ The quick brown fox jumped over the lazy dog\n<\/code><\/pre>\n<h3>Reference to external packages<\/h3>\n<ul>\n<li>Markdown processor: <a href=\"https:\/\/github.com\/russross\/blackfriday\">Blackfriday<\/a><\/li>\n<li>HTML sanitizer: <a href=\"https:\/\/github.com\/microcosm-cc\/bluemonday\">bluemonday<\/a><\/li>\n<\/ul>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Featured image by&nbsp;Egon Elbre [&#8230;]<\/p>\n<p><a class=\"understrap-read-more-link\" href=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-8\/\">Read more &rarr;<\/a><\/p>\n","protected":false},"author":2,"featured_media":582,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_mi_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[52],"tags":[53],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v19.13 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Learning Go - Day 8 - Andr\u00e9 Jacobs<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-8\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Learning Go - Day 8 - Andr\u00e9 Jacobs\" \/>\n<meta property=\"og:description\" content=\"Featured image by&nbsp;Egon Elbre [...]Read more &rarr;\" \/>\n<meta property=\"og:url\" content=\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-8\/\" \/>\n<meta property=\"og:site_name\" content=\"Andr\u00e9 Jacobs\" \/>\n<meta property=\"article:published_time\" content=\"2022-04-28T13:26:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2022-05-27T15:53:03+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/andrejacobs.org\/wp-content\/uploads\/2022\/05\/standing.png\" \/>\n\t<meta property=\"og:image:width\" content=\"548\" \/>\n\t<meta property=\"og:image:height\" content=\"682\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/png\" \/>\n<meta name=\"author\" content=\"Andr\u00e9 Jacobs\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:creator\" content=\"@andrejacobs81\" \/>\n<meta name=\"twitter:site\" content=\"@andrejacobs81\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Andr\u00e9 Jacobs\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-8\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/andrejacobs.org\/study-notes\/learning-go-day-8\/\"},\"author\":{\"name\":\"Andr\u00e9 Jacobs\",\"@id\":\"https:\/\/andrejacobs.org\/#\/schema\/person\/3d38360883015e883c80c2fb875c5a68\"},\"headline\":\"Learning Go &#8211; 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