Go中的文件路径

Question

So this is the example from Programming in Go by Mark Summerfield.

package main

import (
"fmt"
"io/ioutil"
"os"
"path/filepath"
"strings"
)

var britishAmerican = "british-american.txt"

func init() {
    dir, _ := filepath.Split(os.Args[0])
    britishAmerican = filepath.Join(dir, britishAmerican)
}

func main() {
    rawBytes, err := ioutil.ReadFile(britishAmerican)
    if err != nil {
        fmt.Println(err)
    }
    text := string(rawBytes)

    usForBritish := make(map[string]string)

    lines := strings.Split(text, "
")
    fmt.Println(lines)
    for _, line := range lines {
        fields := strings.Fields(line)
        if len(fields) == 2 {
            usForBritish[fields[0]] = fields[1]
        }
    }
    fmt.Println(usForBritish)
}

When I run this code with the init() func commented out, it works perfectly fine. If I leave it in I get this error:

open /var/folders/l6/rdqtyrfd303dw1cz8qvlfcvc0000gn/T/go-    build652175567/command-line-arguments/_obj/exe/british-american.txt: no     such file or directory exit status 1  

My question is, why does the init() func not grab the file from the appropriate directory?

Answer 1

You change the variable britishAmerican in the init function. Without init(), the program looks in the current directory (no path given, only the file name). With init(), it looks in the path where the executable is (os.Args[0]). And with go run main.go, the directory with the executable is not the current working directory.

You should use go build to build the binary and then run it, or you should tell us what you want to achieve (as written by @RoninDev).

---

The MCVE I've mentioned could look like this:

package main

import (
    "io/ioutil"
    "log"
    "os"
    "path/filepath"
)

var filename = "foo.txt"

func init() {
    // change to true and things break
    if false {
        dir, _ := filepath.Split(os.Args[0])
        filename = filepath.Join(dir, filename)
    }
}

func main() {
       // requires a file 'foo.txt' in the current directory
    _, err := ioutil.ReadFile(filename)
    if err != nil {
        log.Fatal(err)
    }
}

It can (of course) be even shorter, but this should be enough for the others in the community to see what is going on.