When you need to restrict a find-and-replace operation to a specific block of text, Vim gives you several approaches. Using the %V atom The most straightforward method is the %V atom, which restricts pattern matching to the current visual selection: :%s/%Vfrom/to/gc This works regardless of the visual mode you used (character, line, or block). The…
To identify the developers who’ve contributed the most commits to a repository, use git log with some text processing: git log –format=’%aN’ | sort | uniq -c | sort -rn This returns a sorted list with commit counts and author names: 247 Paul Phillips 45 Dale Wijnand 12 Yamashita Yuu 10 Gilles Cornu 8 Josh…
Sorting text file lines by their length is useful for analyzing text patterns, finding anomalies, or preparing data for processing. Here are the most practical approaches. Using awk with sort The standard approach combines awk to calculate line length with sort to order them: awk ‘{ print length(), $0 | “sort -n” }’ /path/to/text/file This…
When you run journalctl without options on a system with years of log history, it can take seconds or even minutes to parse everything. The slowness comes from journalctl loading and deserializing potentially gigabytes of journal data. The solution is targeted querying — you almost never need the entire journal, so restrict what journalctl reads…
mpv is a powerful media player for Linux that supports looping videos with minimal configuration. Here’s how to loop videos in fullscreen mode using mpv. Loop a Single Video The simplest way — use the –loop flag: mpv –fullscreen –loop video.mp4 –loop replays the video infinitely. To loop a specific number of times: # Loop…
Bash provides several straightforward ways to test whether a string contains a substring. The best approach depends on your use case and performance requirements. Using [[ ]] with glob patterns The fastest and most Bash-native method is the [[ conditional construct with glob patterns: if [[ “$string” == *”substring”* ]]; then echo “Found it!” fi…
[md] The dd command doesn’t evaluate arithmetic expressions in its parameters. If you try this: $ dd if=/dev/zero of=./4Ktest100M bs=4KB count=25000*9 dd: invalid number ‘25000*9′ You’ll get an error because dd expects literal numeric values, not expressions. The shell doesn’t expand 25000*9 as arithmetic — it’s passed to dd as a literal string. ## Using…
When accepting path input in Bash scripts, users might provide /path/to/dir/ or /path/to/dir. Normalizing these to a consistent format without the trailing slash is a common requirement. The Problem You need a reliable method that: Removes trailing slashes if present Works with both files and directories Handles paths that already lack a trailing slash Works…
Getting the directory path of a running script is a common requirement in bash, whether you’re sourcing files, building paths to config directories, or navigating relative to the script itself. The naive approach often fails with symbolic links or when the script is sourced rather than executed directly. The Problem Using $0 alone is unreliable….
By default, xargs appends its input as arguments at the end of the command. This works fine when you need a utility once per item, but becomes problematic when you need to reference the same input multiple times in different positions. The Problem Consider renaming files by appending .bak to each filename. You might try:…
When you run a command like this in Bash: ssh host1 hostname &; ssh host2 hostname & You get an error: bash: syntax error near unexpected token `;’ The issue stems from how Bash interprets command separators. The & and ; characters are both command terminators, but they serve different purposes, and Bash has strict…
When stop-dfs.sh fails to cleanly terminate DataNode processes, you’re left with orphaned Java processes consuming resources and potentially causing cluster issues. This happens most often after ungraceful cluster shutdowns or when the standard stop script encounters communication problems with specific nodes. Understanding the Problem The typical symptom is stop-dfs.sh reporting that certain nodes have no…
Monitoring directory growth is essential for tracking logs, temporary files, and catching runaway disk usage before it becomes a problem. Linux offers several approaches depending on whether you need simple periodic checks, interactive exploration, or event-driven monitoring. Simple periodic monitoring The watch command repeatedly runs a command at set intervals: watch -n 1 du -sh…
Writing a master thesis means protecting years of work. You need to handle three core concerns: preventing data loss from hardware failure or malware, ensuring 24/7 access to your work, and keeping it private until publication. The solution is version control with remote backup. Git provides local history and recovery, while a private remote repository…
Merging SAM files is a common task in bioinformatics workflows, and while samtools merge works directly with BAM files, you need a different approach for SAM files. The most efficient method leverages the SAM format structure: headers start with @, and alignment records don’t. Why not convert to BAM first? Converting SAM to BAM, merging…
The git diff –word-diff output is clean and readable for tracking changes at the word level instead of line-by-line. If you need that functionality outside a git repository—or just want a standalone tool—wdiff is purpose-built for exactly this. Using wdiff for word-level diffs wdiff compares two files word by word, where a word is defined…
The free command—along with ps, top, kill, pgrep, and dozens of other system utilities—is maintained as part of the procps-ng project. Source repository The source code is hosted at: https://gitlab.com/procps-ng/procps You can clone it with: git clone https://gitlab.com/procps-ng/procps.git cd procps Most distributions package procps-ng, so you likely already have it installed. You can verify the…
Automating keyboard input on Linux is useful for testing, accessibility workflows, and automation scripts. If you need to simulate pressing multiple keys simultaneously and holding them, xdotool is the standard tool for this job. Basic approach with xdotool The keydown and keyup commands let you press and release individual keys without triggering the other. To…
When you’re processing text with varying amounts of whitespace between fields, the standard cut command falls short. Given input like this: a b c d You need a way to reliably extract fields regardless of how many spaces separate them. Here are the practical approaches. Using tr with cut The tr command can normalize whitespace…
When uploading files to HDFS using hdfs dfs -put, the replication factor defaults to the cluster-wide setting in hdfs-site.xml (typically 3). For temporary files, logs, or staging data, you often want a lower replication factor to reduce write latency and disk usage. Override Replication Factor at Upload Time Use the -D flag to pass HDFS…