go files Cheat Sheet

A cheat sheet in English by cizixs

working with files in golang

12,757 views 3,112 downloads 26 Sep 2017 History

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Basic Operations

create empty file	`newFile, err := os.Create("test.txt")`
truncate a file	`err := os.Truncate("test.txt", 100)`
get file info	`fileInfo, err := os.State("test.txt")`
rename a file	`err := os.Rename(oldPath, newPath)`
delete a file	`err := os.Remove("test.txt")`
open a file for reading	`file, err := os.Open("test.txt")`
open a file	`file, err := os.Open("test.txt", os.O_APPEND, 0600)`
close a file	`err := file.Close()`
change file permision	`err := os.Chmod("test.txt", 0777)`
change file ownership	`err := os.Chown("test.txt", os.Getuid(), os.Getgid())`
change file timestamps	`err := os.Chtimes("test.txt", lastAccessTime, lastModifyTime)`

file open flag

`os.O_RDONLY`	open the file read only
`os.O_WRONLY`	open the file write only
`os.O_RDWR`	open the file read write
`os.O_APPEND`	append data to the file when writing
`os.O_CREATE`	create a new file if none exists
`os.O_EXCL`	used with `O_CREATE`, file must not exist
`os.O_SYNC`	open for synchronous I/O
`O_TRUNC`	if possible, truncate file when opened

When opening file with os.OpenFile, flags control how the file behaves.

Hard Link & Symbol Link

create a hard link	`err := os.Link("test.txt", "test_copy.txt")`
create a symbol link	`err := os.Symlink("test.txt", "test_sym.txt")`
get link file info	`fileInfo, err := os.Lstat("test_sym.txt")`
change link file owner	`err := os.Lchown("test_sym.txt", uid, gid)`
read a link	`dest, err := os.ReadLink("link_file.txt")`

A hard link creates a new pointer to the same place. A file will only be deleted from disk after all links are removed. Hard links only work on the same file system. A hard link is what you might consider a 'normal' link.

A symbolic link, or soft link, only reference other files by name. They can point to files on different filesystems. Not all systems support symlinks.

Read and Write

write bytes to file	`n, err := file.Write([]byte("hello, world!\n"))`
write string to file	`n, err := file.WriteString("Hello, world!\n")`
write at offset	`n, err := file.WriteAt([]byte("Hello"), 10)`
read to byte	`n, err := file.Read(byteSlice)`
read exactly n bytes	`n, err := io.ReadFull(file, byteSlice)`
read at least n bytes	`n, err := io.ReadAtLeast(file, byteSlice, minBytes)`
read all bytes of a file	`byteSlice, err := ioutil.ReadAll(file)`
read from offset	`n, err := file.ReadAt(byteSlice, 10)`

Work with directories

create a directory	`err := os.Mkdir("myDir", 0600)`
recursively create a directory	`err := os.MkdirAll("dir/subdir/myDir", 0600)`
delete a directory recursively	`err := os.RemoveAll("dir/")`
list directory files	`fileInfo, err := ioutil.ReadDir(".")`

Shortcuts

quick read from file	`byteSlice, err := ioutil.ReadFile("test.txt")`
quick write to file	`err := ioutil.WriteFile("test.txt", []byte("Hello"), 0666)`
copy file	`n, err := io.Copy(newFile, originFile)`
write string to file	`io.WriteString(file, "Hello, world")`

Temporary files and directories

create temp dir	`ioutil.TempDir(dir, prefix string) (name string, err error)`
create temp file	`ioutil.TempFile(dir, prefix string) (f *os.File, err error)`

References

Working with Files in Go

golang os standard library

golang ioutil standard library

golang iou standard library

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