Programming

Programming languages and software development

Programming

Decoding URL-Encoded Strings in Python
ByEric Ma Apr 1, 2018Apr 11, 2026

URL encoding (percent-encoding) converts special characters into a format safe for transmission over HTTP. In Python, the urllib.parse module provides straightforward functions for decoding these strings. Basic Decoding with unquote The unquote() function is the standard approach: from urllib.parse import unquote encoded_url = “https://example.com/search?q=hello%20world” decoded_url = unquote(encoded_url) print(decoded_url) # Output: https://example.com/search?q=hello world This handles the…

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Programming

Generate a Git Patch File for a Specific Commit
ByEric Ma Mar 30, 2018Apr 11, 2026

Patch files are essential for projects that use email-based code review or maintainer-driven workflows. They’re especially common in Linux kernel development, embedded systems, and projects that don’t rely on pull requests. Creating a patch from a single commit The standard approach is git format-patch: git format-patch -1 <commit-hash> This creates a .patch file containing the…

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Programming

Exclude a Package from a Specific Repository in Yum
ByQ A Mar 29, 2018Apr 11, 2026

When managing packages on RHEL, CentOS, AlmaLinux, or Fedora, you sometimes need to prevent a package from being installed or updated from a particular repository. This is useful when multiple repos provide the same package and you want to control which version gets pulled in. Repository-specific exclusions with DNF Modern systems use DNF (which supersedes…

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Programming

Cleaning Up Git Commit History: A Practical Guide
ByQ A Mar 28, 2018Apr 11, 2026

“Cleaning” history usually means rewriting it to remove large files, sensitive data, or to squash messy commits into logical units. This is destructive—it rewrites history and affects anyone who’s cloned the repo. Only do this on branches you control or coordinate with your team first. git filter-repo: The Standard Tool git filter-repo replaced the deprecated…

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Programming

Handling `]]>` in XML CDATA Sections
ByQ A Mar 26, 2018Apr 11, 2026

In XML, CDATA (Character Data) sections let you include text without worrying about XML special characters. Everything inside <![CDATA[ and ]]> is treated as literal text — no parsing, no entity references. This is useful for embedding code snippets, scripts, or any content with lots of <, >, or & characters. The catch: you can’t…

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Programming

Resizing a KVM Virtual Disk: A Step-by-Step Guide
ByWeiwei Jia Mar 24, 2018Apr 11, 2026

Expanding a VM’s storage is a routine operation in KVM environments. The process has two distinct phases: expanding the raw disk capacity and then growing the partitions and filesystems to use that space. Resizing the Disk Image The first step is to increase the virtual disk size using qemu-img: qemu-img resize disk.qcow2 +10G This adds…

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Programming

Using Type Erasure in C++11 Lambda Parameters
ByEric Ma Mar 24, 2018Apr 11, 2026

In C++11, lambda parameters required concrete types. Creating a truly generic lambda meant wrapping the logic in a template struct — awkward and verbose. C++14 introduced generic lambdas using auto for parameter deduction, eliminating this friction entirely. Basic Generic Lambda Syntax The simplest approach uses auto in lambda parameters: auto add = [](auto a, auto…

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Programming

Checking if a File is a Block Device in Python
ByQ A Mar 24, 2018Apr 11, 2026

On Linux, block special files represent hardware devices like hard drives, SSDs, and other block devices. They’re typically found in /dev and can be identified using Python’s stat module combined with os.stat(). The Standard Approach import os import stat path = “/dev/sda” try: mode = os.stat(path).st_mode if stat.S_ISBLK(mode): print(f”{path} is a block device”) except FileNotFoundError:…

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Programming

Opening or Creating a File in Read-Write Mode with C++
ByQ A Mar 24, 2018Apr 11, 2026

When you need to open a file for both reading and writing, creating it if it doesn’t exist, C++ offers several approaches. The choice depends on your project’s requirements and how much control you need over the process. Using std::fstream The most straightforward modern approach uses std::fstream, part of the standard library: #include <fstream> std::fstream…

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Programming

Escaping Special Characters in Bash Strings
ByQ A Mar 24, 2018Apr 11, 2026

When passing quoted strings through SSH, shell quoting rules can cause unexpected behavior. The classic issue: ssh user@host cmd “my string” On the remote host, this executes as: cmd my string Instead of treating “my string” as a single argument, the shell splits it. This happens because quotes are processed by your local shell first,…

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Programming

Checking if a String Starts With Another in C++
ByEric Ma Mar 24, 2018Apr 11, 2026

C++20 introduced std::string::starts_with(), which is the most straightforward way to check if a string begins with a specific substring: #include <iostream> #include <string> int main() { std::string text = “big string here…”; std::cout << std::boolalpha; std::cout << text.starts_with(“big”) << std::endl; // true std::cout << text.starts_with(“small”) << std::endl; // false std::cout << text.starts_with(“big string”) << std::endl;…

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Programming

Splitting and Iterating Strings by Delimiter in C++
ByEric Ma Mar 24, 2018Apr 11, 2026

Splitting strings by a delimiter is a common task in systems programming. C++ doesn’t provide a built-in split function like Python, but you can implement one efficiently using the standard library. Using std::istringstream and getline() The standard approach uses std::istringstream with std::getline(). The getline() function accepts a delimiter parameter, allowing you to extract tokens until…

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Programming

Getting the Canonical Path Without Following Symlinks in Python
ByQ A Mar 24, 2018Apr 11, 2026

The Linux command readlink -m resolves a path to its absolute, canonical form, following all symlinks and resolving .. and . components. Python provides several ways to do this, depending on your needs and Python version. Using pathlib.Path.resolve() The modern standard approach uses pathlib: from pathlib import Path canonical_path = Path(“./../folder/./file.txt”).resolve() print(canonical_path) Path.resolve() returns an…

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Programming

Accessing Elements in a const Map with operator[] in C++
ByEric Ma Mar 24, 2018Apr 11, 2026

Using operator[] on a const map will fail to compile. This code: #include <iostream> #include <string> #include <map> std::int64_t count(const std::map<std::string, std::int64_t>& map) { return map[“one”] + map[“two”]; } int main() { std::map<std::string, std::int64_t> map = { {“one”, 1}, {“two”, 2} }; std::cout << count(map) << std::endl; return 0; } produces a compiler error: error:…

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Programming

Configuring Vim to Indent C++11 Lambdas Properly
ByEric Ma Mar 24, 2018Apr 11, 2026

Vim’s default indentation can mangle C++11 lambdas, treating them like nested blocks instead of closures. The lambda body gets indented too far relative to the enclosing statement. The Problem Given this code: #include <iostream> #include <string> #include <vector> #include <algorithm> int main() { std::vector<std::string> strs({“one”, “two”}); std::vector<std::string> newstrs; std::transform(strs.begin(), strs.end(), std::back_inserter(newstrs), [](const std::string& s) ->…

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Programming

Hide Your Private IP from Thunderbird Email Headers
ByEric Ma Mar 24, 2018Apr 11, 2026

Thunderbird can leak your LAN IP address in SMTP email headers, even though the mail server itself only sees your public IP. This happens because Thunderbird sends its local IP during the HELO/EHLO handshake with the SMTP server, and that information gets recorded in the email header. For example, you might see: Received: from [192.168.1.2]…

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Programming

How to View Partition Start and End Sectors with Parted
ByEric Ma Mar 24, 2018Apr 11, 2026

By default, parted displays partition boundaries in bytes. To view start and end positions in sectors instead, you need to set the unit explicitly using the unit command. Using the unit command The unit subcommand in parted sets the display unit for locations and sizes. The syntax is straightforward: parted /dev/sda unit s print The…

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Programming

Prevent Line Wrapping in Evolution’s Compose Window
ByEric Ma Mar 24, 2018Apr 11, 2026

Evolution automatically wraps long lines in Plain Text mode, which can be frustrating if you need to preserve line breaks exactly as you’ve written them. Unlike some email clients, Evolution doesn’t support “soft wrapping” where text reflows visually in the composer but sends without hard line breaks. Using External Editor The most straightforward approach is…

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Programming

Enabling Email Auto-Completion in Evolution
ByEric Ma Mar 24, 2018Apr 11, 2026

GNOME Evolution’s email address auto-completion works by querying your local address books and, optionally, external sources. Here’s how to get it working properly. Check Your Address Books Evolution pulls auto-completion suggestions from multiple sources: Personal address book (local contacts you’ve added) On This Computer (system-wide contacts) Synced contact sources (Google, CalDAV, CardDAV, LDAP) To see…

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Programming

Applying Email Sort Order to All Folders in Evolution
ByEric Ma Mar 24, 2018Apr 11, 2026

Evolution stores sort preferences individually per folder by default. If you want emails consistently sorted across your entire mailbox, you need to set a global default. Steps Open Evolution and navigate to Edit → Preferences Go to Mail Preferences → General Locate the Default Sorting section Choose your preferred Sort by option (Date Received, Subject,…

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