Accidentally pushing a tag to a remote repository happens frequently. Whether you tagged the wrong commit, used an incorrect version number, or triggered an unintended CI/CD pipeline, you need a clean way to remove it. The Basic Command Delete a remote tag using git push with the –delete flag: git push origin –delete <tagname> For…
Querying transaction details from a Hyperledger Fabric ledger is critical for auditing, compliance verification, and debugging chaincode behavior. The QSCC (Query System Chaincode) provides the GetTransactionByID function to retrieve complete transaction metadata including endorsements, read/write sets, and validation status. This guide uses Hyperledger Fabric 2.5+ on Ubuntu 24.04 LTS with the test-network from fabric-samples. Environment…
Zlib is a foundational open-source compression library implementing the DEFLATE algorithm. It powers gzip, PNG, HTTP compression, and countless applications. While Ubuntu’s package repositories provide pre-built binaries, compiling from source lets you use the latest version, customize the installation path, enable specific compile-time features, and maintain multiple versions simultaneously. This guide covers building zlib on…
Go doesn’t have a dedicated FileExists() function. Instead, use os.Stat() to retrieve file metadata and inspect the error type to determine what actually happened. Basic File Existence Check import “os” func fileExists(path string) bool { _, err := os.Stat(path) return !os.IsNotExist(err) } os.Stat() returns an error only if something goes wrong. The key is using…
PHP lets you call functions dynamically when you don’t know the function name until runtime. This is essential for plugin systems, routing handlers, API dispatchers, and configuration-driven logic. The approach you choose affects both performance and safety. Direct Variable Function Invocation The simplest approach treats a string variable as a callable: $func = ‘strlen’; echo…
The stat() system call is the traditional approach for checking file existence: #include <sys/stat.h> int file_exists(const char *path) { struct stat buffer; return (stat(path, &buffer) == 0); } This returns 1 if the file exists, 0 otherwise. The stat() call fills the buffer with file metadata, but when checking existence alone, you’re mainly interested in…
“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…
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…
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…
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,…
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:…
For iterating through directories and files in C++, you have several options depending on your needs and C++ standard version. Using <filesystem> (C++17 and Later — Recommended) The modern approach uses std::filesystem, which is cleaner, safer, and handles cross-platform differences for you: #include <filesystem> #include <iostream> #include <string> namespace fs = std::filesystem; int ListDir(const std::string&…
The stat() system call is the standard way to retrieve file metadata on Linux, including modification time (mtime). It’s fast, portable, and gives you access to nanosecond-precision timestamps. Basic Approach with stat() #include <sys/stat.h> #include <stdio.h> struct stat st; if (stat(“path/to/file”, &st) == -1) { perror(“stat failed”); return 1; } printf(“Mtime (seconds): %ld\n”, st.st_mtime); printf(“Mtime…
Determining whether a path points to a directory or regular file is a common task in system programming. You need to stat the path and inspect the file mode. Using lstat() and stat macros The lstat() system call retrieves file metadata into a struct stat. For a given path, you can use the standard macros…
If you’re getting this error when running bibtex on your auxiliary file, it typically means your document has no citations, even though BibTeX is being invoked: This is BibTeX, Version 0.99d (TeX Live 2015/Debian) The top-level auxiliary file: main.aux The style file: latex8.bst I found no citation commands—while reading file main.aux (There was 1 error…
You need to detect whether STDERR (file descriptor 2) is connected to a terminal or redirected to a file or pipe. This is useful for conditional logging, color output, or error handling that depends on the output destination. Using file descriptor tests The primary method is the -t test operator, which checks if a file…
The NameNode in HDFS maintains the filesystem namespace in memory. The Secondary NameNode (or Checkpoint Node in HA setups) periodically merges the namespace image (fsimage) with the edit logs to create a new checkpoint. Understanding how to force this process is essential for cluster maintenance and recovery operations. How Checkpointing Works The checkpoint process combines…
By default, Python buffers stdout when it’s not connected to a terminal — typically when you redirect output to a file, pipe to another command, or run inside a container. This buffering can hide output until the buffer fills or the program exits, making debugging and log monitoring difficult. Using the flush parameter The simplest…
[md] The error ValueError: zero length field name in format occurs when using implicit positional arguments in .format() strings with Python versions that don’t support this syntax. ## The Problematic Code print(‘== {} SPF’.format(d)) This raises ValueError: zero length field name in format on older Python interpreters. ## Why This Happens The {} syntax without…
The fastestmirror plugin automatically selects the fastest package mirror for your system. While useful, you might want to disable it if you’re experiencing slow mirror detection, prefer a specific mirror, or troubleshoot package manager issues. The plugin is provided by yum-plugin-fastestmirror (on older EL7 systems) or as part of DNF’s core functionality (EL8+). Unlike older…