Programming Tutorials and Coding Guides

Shell script parallel execution in Bash: background jobs, wait, and per-PID exit codes. Bash parallelize for loop, parallel shell patterns, and how to run a script on Linux before scaling out.

Exponentiation in JavaScript with the ** power operator and Math.pow: numbers, BigInt, right-associativity, unary minus precedence, NaN ** 0, **= compound assignment, and when to prefer Math.pow on older engines. Each …

Zap logger and zap logging with go.uber.org/zap, zap sugaredlogger and sugaredlogger vs Logger, golang zap and zap golang structured fields, zap request id with With or Infow, golang zap logger setup, levels, and …

Linux login history: view and check login history, login logs, and Linux SSH login history via last, wtmp, auth.log or /var/log/secure, and journalctl. Optional script to summarize successful and failed SSH attempts.

Grep word after match, grep everything after match, grep characters after match, grep next line after match, and awk print after match on Linux (GNU grep -P with \K, -A, match/substr). Brief patterns for the word before …

Bash: measure time of a command, script execution time, and elapsed time (wall clock vs CPU). Use the time builtin, TIMEFORMAT, SECONDS, or EPOCHREALTIME; print duration on exit with trap.

Bash get script name, get current script name, get script path, and get script directory (script dir). Use $0, basename, BASH_SOURCE[0], dirname, cd+pwd, and readlink -f on Linux; handle sourced scripts safely.

Use find with sha256sum (or md5sum) to list identical files on Linux, group by hash, then delete duplicate copies interactively or after a dry-run—plus how “duplicate by name” differs from same content.

What echo does on Linux, the echo -n flag (no trailing newline), why echo n is not echo -n, how echo -e handles backslash escapes like \n, and when to use printf instead.

Bash patterns to remove an element from an array, drop the first item, dedupe (bash array remove duplicates), and subtract all values of one array from another using loops or an associative map.

Onboarding-style Bash: read usernames from a file, create multiple Linux users with useradd, optional custom shell and home under /home, per-user passwords with chpasswd, force change on first login, and test with su or …

Build a bash progress bar and bash loading bar in the terminal with carriage return redraws, reusable functions, multi-step jobs, plus pv for pipe byte counts and dialog for a gauge widget.

Bash counter patterns: C-style for loop counter, bash while loop counter, increment with (( )) and let, bash for count over a list, and a small script counter over files—plus links to deeper increment and loop guides.

Count how many times a word or substring appears in a file, count lines and words with wc, whole-word matches with grep -E, and build a frequency table with awk or sort/uniq.

Find top CPU and memory consuming processes on Linux with ps, top, sar, and pidstat; sample output after controlled stress; Bash scripts that append metrics to a file and ideas for email alerts.

Bash patterns to see if a string contains a substring or character, if it is only digits, if it starts with a prefix, and how [[ =~ ]] and globs differ— with quoting, empty-string gotchas, and a short locale note.

Linux and Bash ways to check if a process is running, if a PID still exists, and how to stop a second copy of the same shell script—using kill -0, pidof, pgrep, and flock with sane lock files and cleanup.

Bash while loops: `while`/`do`/`done`, any command as the condition, `while true` with `break` and `continue`, `while read` over files, do-while style with `while true`, nested loops, and `break` vs `exit`.

Bash script arguments and bash script parameters with $0–$9, $#, "$@", shift, and a while/case example; missing-flag values, $# checks, and links to getopts and forwarding all args.

Bash check if file exists with [[ -f ]], test -e, and [ ]; bash if file exists patterns with if/else; symlinks and broken links; check if file exists on Linux with find and stat; quoting, exit codes, and pitfalls.

Bash trap Ctrl+C (SIGINT): linux ctrl c signal basics, trap INT and trap ctrl-c patterns, ignore with trap empty string, EXIT cleanup, quoting pitfalls, and subshell vs child-process behavior.

Bashrc vs bash_profile and profile vs bashrc: when Bash reads ~/.bashrc, ~/.bash_profile, and ~/.profile on login and new terminals, Debian vs Red Hat patterns, and what /etc/skel ships for new users.

Bash until vs while using exit status: bash until loop runs while a command fails, while loop bash runs while it succeeds. Examples for counters, wait until ready, and while read line-by-line.

Bash multiple arguments with positional parameters, bash pass all arguments via "$@", bash pass multiple arguments to a function, forwarding to another script, and bash pass function over SSH with typeset -f or declare …

Bash increment variable and bash add 1 to variable with $(( )), ((++)), bash increment variable in loop (for/while), bash increment counter patterns, let, and post vs pre-increment pitfalls.

Bash if else and bash if then else with elif chains, if else in bash shell scripts, combining conditions, nested if, exit-status semantics, and [[ ]] vs [ ] with links to string and number comparisons.

Bash getopts tutorial: optstring, OPTARG, OPTIND, opterr, bash getopts leading colon behavior for missing option arguments vs invalid options, bash getopts example scripts, shift after parsing, and getopt bash vs getopts …

Bash define function with name() or function keyword, bash function example calls, bash script function arguments ($1, $@), local vs global variables, return exit codes, and capturing output.

Bash for loop and for loop in bash: iterate words, arrays with "${a[@]}", C-style for ((i=0;i

Bash concatenate strings and bash string concat with ${a}${b}, bash append to string using +=, join strings with separators, brace pitfalls (${var}_), loops, newlines, and printf-based joining.