Julia File Read/Write

Julia provides some basic functions to handle files:

• open()- Open file
• read()- Read file content
• close()- Close file

To read or write data from a file, you need to use a file handle.

A file handle is actually a pointer, and the pointer points to a certain position in the file.

To read data from a file, the application first calls an operating system function, passes the file name, and selects a path to the file to open it. The function that opens the file returns a sequence number, i.e., the file handle. This file handle is the unique identifier for the opened file.

open() Function

Julia can useopen()function to open a file, this function returns a file handle:

Syntax format:

open(filename, mode)

filenameis the file name,modeis the read/write mode, which can be the following values:

# Windows 打开文件
foo = open("D://example-test//julia//example-file.txt")

# Linux 或 Mac 打开文件 
foo = open("./example-test/julia/example-file.txt")

close() Function

After finishing file operations, we need to close the file; otherwise it may cause problems such as resource leaks. To close a file, useclose()function:

# 关闭上面代码中打开文件返回的 foo 句柄
close(foo)

In Julia, we recommend that any file processing function be wrapped in adostatement block. The advantage of wrapping file processing functions in a do statement block is that when the block finishes execution, the opened file will be automatically closed, i.e., it will automatically call the close() function, as shown below:

The above code does not need to call the close() function, because it will automatically call the close() function to close the file.

Next, we create a test.jl file with the following code:

Execute the above code:

$ julia test.jl

After successful execution, a example-file.txt file is created in the directory of the current code file, and the written content is as follows:

Hello world!
Example Julia Test

We can usedostatement, so there is no need to useclose()function:

Execute the above code:

$ julia test.jl

After successful execution, a example-file.txt file is created in the directory of the current code file, and the written content is as follows:

Hello world!
Example Julia Test
使用 do 语句

read() Function

Using the read() function, we can read the entire contents of a file, for example:

txt = read(foo, String)

Execute the above code, the output result is as follows:

$ Julia test.jl
Hello world!
Example Julia Test

doIn the statement, useread()function:

open(filename) do file
    read(file, String)
end

Execute the above code, the output result is as follows:

$ julia test.jl
Hello world!
Example Julia Test

We can usereadlines()function to put the file content into an array line by line, with the following syntax:

readlines(io::IO=stdin; keep::Bool=false)
readlines(filename::AbstractString; keep::Bool=false)

Execute the above code, the output result is as follows:

$ julia test.jl
["Hello world!\n", "Example Julia Test\n", "使用 do 语句"]

We can also useeachline()function to process the file line by line:

Execute the above code, the output result is as follows:

$ julia test.jl
12, Hello world!
17, Example Julia Test
8, 使用 do 语句

We can also get the current line number:

Execute the above code, the output result is as follows:

$ julia test.jl
1 Hello world!
2 Example Julia Test
3 使用 do 语句

stat() Function

stat() The function is used to obtain file information, the format is as follows:

stat(pathname) 

Execute the above code, the output result is as follows:

$ julia test.jl
desc: example-file.txt
device: 16777222
inode: 35345094
mode: 33188
nlink: 1
uid: 501
gid: 20
rdev: 0
size: 47
blksize: 4096
blocks: 8
mtime: 1.6524042534674733e9
ctime: 1.6524042534674733e9

abspath() Function

abspath() The function is used to get the absolute path of a file, and can be mapped to a list:

stat(pathname) 

Execute the above code, the output result is as follows:

["/Users/EXAMPLE/example-test/.Rhistory", "/Users/EXAMPLE/example-test/.vscode", 
...

More Functions

The following table lists other related functions for handling files: