Short code examples on reading and writing to text files.
Open file, print contents line by line
If you can print a file line by line, of course, you can do whatever you like with that line.
with open('filename.txt', 'r') as f:
for line in f:
print(line.rstrip())
def handle_line(line):
print(line)
map(handle_line, [line.rstrip() for line in open('filename.txt', 'r')])
using System;
using System.Text;
namespace MyProgram
{
public class Program
{
public static void Main(string[] args)
{
using (var reader = new System.IO.StreamReader(System.IO.File.OpenRead("filename.txt"), Encoding.UTF8))
{
string line;
while ((line = reader.ReadLine()) != null)
{
Console.WriteLine(line);
}
}
}
}
}
const fs = require('fs')
const data = fs.readFileSync('filename.txt', 'UTF-8')
const lines = data.split(/\r?\n/)
lines.forEach((line) => {
console.log(line
})
const fs = require('fs');
const readline = require('readline');
const rl = readline.createInterface({
input: fs.createReadStream('file.txt'),
output: process.stdout,
terminal: false
});
rl.on('line', (line) => {
console.log(line);
});
foreach ($line in Get-Content .\filename.txt) {
Write-Output $line
}
Const ForReading = 1
Dim fso
Set fso = WScript.CreateObject("Scripting.FileSystemObject")
Dim file, line
Set file = fso.OpenTextFile("filename.txt", ForReading)
Do While file.AtEndOfStream = False
line = file.ReadLine
WScript.Echo line
Loop
file.Close
Create a new file, write text into it
So many combinations amongst various languages on handling whether the file exists or not. I’ll keep it simple here: create or overwrite.
with open('newfilename.txt', 'w') as f:
f.write('line 1\n')
f.write('line 2\n')
namespace MyProgram
{
public class Program
{
public static void Main(string[] args)
{
using (var writer = new System.IO.StreamWriter("newfilename.txt"))
{
writer.WriteLine("line 1");
writer.WriteLine("line 2");
}
}
}
}
const fs = require('fs')
const writer = fs.createWriteStream('newfilename.txt')
writer.write('line 1\n')
writer.write('line 2\n')
# this will create or overwrite newfilename.txt "line 1" | Out-File -FilePath .\newfilename.txt Add-Content .\newfilename.txt "line 2"
# this will only create, error if already exists New-Item .\newfilename.txt Set-Content .\newfilename.txt "line 1" Add-Content .\newfilename.txt "line 2"
Dim fso
Set fso = WScript.CreateObject("Scripting.FileSystemObject")
Dim file
Set file= fso.CreateTextFile("newfilename.txt", True, False) ' True = overwrite, False = unicode
file.WriteLine "line 1"
file.WriteLine "line 2"
file.Close
Append to an existing file
Each of these examples will create the file if it doesn’t exist, or append to it if it does – except for VB Script, which will error.
with open('priorfilename.txt', 'a') as f:
f.write('line 3')
namespace MyProgram
{
public class Program
{
public static void Main(string[] args)
{
using (var writer = new System.IO.StreamWriter("priorfilename.txt", true)) // true = append
{
writer.WriteLine("line 3");
}
}
}
}
const fs = require('fs')
const writer = fs.createWriteStream('priorfilename.txt', {'flags': 'a'})
writer.write('line 3\n')
Add-Content .\priorfilename.txt "line 3"
Const ForAppending = 8
Dim fso
Set fso = WScript.CreateObject("Scripting.FileSystemObject")
Dim file
Set file= fso.OpenTextFile("priorfilename.txt", ForAppending)
file.WriteLine "line 3"
file.Close
Check if a file exists
import os
if os.path.exists('filename.txt'):
print('It exists')
using System;
namespace MyProgram
{
public class Program
{
public static void Main(string[] args)
{
if (System.IO.File.Exists("filename.txt"))
{
Console.WriteLine("It exists");
}
}
}
}
const fs = require('fs')
if (fs.existsSync('filename.txt')) {
console.log('It exists')
}
If (Test-Path .\filename.txt -PathType Leaf) {
Write-Output "It exists"
}
Dim fso
Set fso = CreateObject("Scripting.FileSystemObject")
If fso.FileExists("filename.txt") Then
WScript.Echo "It exists"
End If