Temporary files are essential for any non-trivial Bash script. Whether you’re processing data, staging changes, or handling inter-process communication, you need reliable ways to create uniquely-named files that won’t collide with other processes. Using mktemp The standard and most reliable approach is mktemp, which generates a cryptographically random temporary filename: tmpfile=$(mktemp) echo “Temporary file created…
Sending output to stderr keeps error messages separate from normal program output, making it easier to redirect and filter logs in shell scripts and pipelines. Basic Approach with fmt The simplest method uses fmt.Fprintln() with os.Stderr: package main import ( “fmt” “os” ) func main() { fmt.Fprintln(os.Stderr, “This is an error message”) } This writes…
The Windows Start Menu pulls shortcuts from two key directories. Understanding where these files live is essential if you’re managing deployments, troubleshooting pinned apps, or automating setups. User-Specific Start Menu User-scoped shortcuts go here: C:\Users\<YourUsername>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs This directory contains all the Start Menu shortcuts specific to your user account. Shortcuts you create or applications install…
To check whether a function exists in Bash, use the type builtin with the -t option. This returns a string identifying what the name is: alias, keyword, function, builtin, or file. Basic Check The simplest approach: if [[ $(type -t f1) == “function” ]]; then echo “f1 is defined as a function” fi This works…
Bash maintains a set of built-in options that control script behavior. You disable them using set +o followed by the option name, or with short flags like set +x. The Basic Syntax set +o option-name Or using short flag notation: set +x The + sign disables an option; – enables it. This works for both…
You need to check whether a directory exists in your $PATH variable. This is useful when verifying that a tool installation succeeded, or when debugging shell initialization scripts. The regex approach Since $PATH uses colons as separators, a regex is the most straightforward method: if [[ “$PATH” =~ (^|:)”/usr/local/mytool/bin”(:|$) ]]; then echo “Directory found in…
When running scripts as root, you often need to execute commands with the environment of a different user. The most reliable way to retrieve another user’s PATH is by spawning a login shell under that user’s context. Basic Approach user1path=$(su – user1 -c ‘echo $PATH’) This spawns a login shell (-) as user1 and outputs…
The scp command handles multiple files efficiently, whether you’re pushing to a remote server or pulling from one. Here are the practical approaches for copying multiple files from remote to local. Brace Expansion Use brace expansion to specify discrete files: scp user@remote:file{1,2,3} ./ This works well when you have a known set of files with…
When you source a script using . script.sh or source script.sh, the $0 variable doesn’t point to the sourced script—it stays as the path of the parent shell or calling script. This creates a problem if you need the sourced script to know its own location. The solution: use ${BASH_SOURCE[0]} The ${BASH_SOURCE[0]} variable holds the…
The tilde expansion ~username works fine when the username is literal, but fails when the username is stored in a variable like ~$user. Bash doesn’t perform tilde expansion on variables by default—it only expands ~ at the beginning of a word before variable expansion happens. Using eval The most common approach is to use eval:…
When you try to unmount a filesystem, Linux sometimes refuses with a “device is busy” error. This safety mechanism prevents data loss when processes are actively using the filesystem. But there are legitimate cases where you need to force an unmount: a dead NFS server, a failed USB device, or a hung mount that won’t…
When Linux fails to boot with the error message “sulogin: can not open password database” despite /etc/passwd and /etc/shadow appearing intact, SELinux is often the culprit. The files exist and have correct content, but SELinux context labels are missing or corrupted, preventing the login process from reading them. Diagnose the Problem Boot into the initramfs…
Backing up text messages from Android works best through Google Messages for real-time web access, or via ADB and third-party tools for local archives. Your approach depends on whether you need cloud sync, local storage, or both. Google Messages for Web (Easiest) The simplest method for most users is Google Messages, which syncs SMS and…
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(), $0 | “sort -n” }’ /path/to/text/file This…
Bash provides several straightforward ways to test whether a string contains a substring. The best approach depends on your use case and performance requirements. Using [[ ]] with glob patterns The fastest and most Bash-native method is the [[ conditional construct with glob patterns: if [[ “$string” == *”substring”* ]]; then echo “Found it!” fi…
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 shell arithmetic expansion The…
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…