This shell script implements an advanced string pattern matching utility using extended regular expressions. It allows users to define complex search patterns and apply them to multiple input strings. The script includes...

The `match_advanced_pattern` function takes a regular expression and a list of strings as input. It first attempts a basic validation of the regex pattern to catch immediate syntax errors, returning an error code if invalid. It then iterates through each provided string. For empty strings, it skips processing. The core matching is done using `grep -qE`, which checks for the existence of a match without outputting the line itself, making it efficient for just determining if a pattern exists. The script collects indicators of matches found. If no matches are found across all strings, a message is printed. The time complexity is roughly O(N * M * L), where N is the number of input strings, M is the average length of an input string, and L is the complexity of the regex matching engine for the given pattern. Space complexity is O(K) where K is the number of matches found, stored in the `results` array. Edge cases handled include invalid regex syntax, no input strings, and empty input strings. The correctness relies on the `grep` utility's accurate implementation of POSIX Extended Regular Expressions.

function match_advanced_pattern(pattern, input_strings): initialize results list initialize error_occurred flag to false try to validate pattern syntax: if invalid: print error message to stderr set error_occurred to tru...

This shell script defines a function `sum_array_elements` that calculates the sum of numeric elements within a given array. It iterates through the array elements, checks if each element is a valid integer using a regula...

The `sum_array_elements` function takes an array's elements as separate arguments. It initializes a `sum` variable to 0 and `element_count` to track the number of elements processed. It iterates through each provided argument (`element`). Inside the loop, it uses a regular expression `^-?[0-9]+$` to validate if the `element` is an integer (allowing for an optional leading minus sign). If it's a valid integer, it's added to the `sum` using arithmetic expansion `$((...))`. If not, a warning is printed to standard error, and the element is skipped. After the loop, it checks if `element_count` is zero, indicating an empty array, and prints a specific message. Finally, it prints the calculated sum. The time complexity is O(N * R), where N is the number of elements in the array and R is the time complexity of the regex check (typically very fast for this simple pattern). The space complexity is O(1) as it only uses a few variables to store the sum and count.

function sum_array_elements(elements...): initialize sum = 0 initialize element_count = 0 for each element in elements: increment element_count if element matches regex "^-?[0-9]+$": add element to sum else: print warnin...

This script demonstrates essential error handling in shell scripting. It performs a series of operations (directory creation, file copying, simulated processing) and includes checks after each critical step. The `set -e`...

The script utilizes two primary methods for error handling. First, `set -e` is invoked at the beginning. This option causes the shell to exit immediately if any command fails (returns a non-zero exit status). This provides a baseline level of safety, preventing subsequent commands from running in an invalid state. Second, explicit checks are performed using `if ! command; then ... fi` or by checking the return status of functions. For instance, the `_simulate_processing` function returns 1 on failure, and the main script checks this return value. If the function fails, the script prints a custom error message and exits. This combination of `set -e` and explicit checks allows for both automatic termination on general errors and tailored error reporting for specific critical operations. The time complexity is O(N*M) where N is the number of steps and M is the average time for each step. Space complexity is O(1) for the script itself.

1. Set the shell option `set -e` to exit on error. 2. Define configuration variables (directory, source file, output file). 3. Define a helper function `_simulate_processing` that takes input and output filenames: a. Che...

This script implements atomic log file rotation. It uses `mv` for an atomic rename and `gzip` for compression. A `trap` mechanism is employed to catch signals like SIGINT and SIGTERM, ensuring that a log rotation occurs...

The core of this script is the `_rotate_logs` function. It first checks if the current log file (`app.log`) exists and is not empty. If so, it renames the current log file to a temporary name (`app.log.timestamp.tmp`), compresses it using `gzip`, and then atomically renames the compressed file to its final name (`app.log.timestamp.gz`). The `mv` command is atomic on POSIX systems when source and destination are on the same filesystem, preventing data loss. The `_cleanup_old_backups` function uses `find`, `sort`, and `head` to identify and remove older backup files, keeping only the `MAX_BACKUPS` most recent ones. The `trap` command ensures that `_signal_handler` is called upon receiving SIGINT or SIGTERM, executing `_rotate_logs` before exiting. This ensures that any buffered log data is saved and rotated properly. Time complexity for rotation is dominated by `mv` and `gzip`, which are typically efficient. Cleanup involves `find` and `sort`, which can be O(N log N) in the worst case for N backup files.

1. Define constants for log directory, log file name, and maximum backups. 2. Define a function `_ensure_log_dir` to create the log directory if it doesn't exist. 3. Define a function `_rotate_logs`: a. Get the current t...

This script demonstrates batch processing of files found by `find`. It uses `find -print0` to generate a null-terminated list of files, which is then piped to a `while read` loop. The loop is configured with `IFS=` and `...

The script leverages `find` with the `-print0` option to produce a stream of filenames separated by null characters. This is the most robust way to handle arbitrary filenames in shell scripting. The output is piped to a `while` loop. Inside the loop, `IFS=` prevents leading/trailing whitespace stripping, `-r` prevents backslash interpretation, and `-d ''` sets the delimiter to the null character, ensuring that each `read` command correctly captures a full filename, including spaces and special characters. The `_process_file` helper function then performs the desired operations on the filename. Error handling is included for the search directory and for individual file processing. The time complexity is primarily determined by `find`'s traversal and the processing time for each file. If there are N files and processing each takes M time, the total is roughly O(N*M). Space complexity is O(1) for the script itself, plus the space required to hold one filename at a time in the `read` command.

1. Define the search directory and file pattern. 2. Define a helper function `_process_file` that takes a filename, performs operations (e.g., count lines, display head), and returns success or failure. 3. In the main ex...

This script aggregates logs from multiple sources into a single file. It uses `tail -f` to continuously monitor each specified log file and pipes their output. The `tee -a` command then appends this combined stream to a...

The script initializes by clearing or creating the main output log file. It then iterates through a list of log files, checking if each is readable using a helper function `_is_readable`. For each readable file, it constructs a `tail -f` command. These commands are then chained together using pipes (`|`) and the entire sequence is executed using `eval`. The final output of all `tail -f` processes is piped to `tee -a`. `tee -a` duplicates the input stream: one copy is appended to the specified `OUTPUT_LOG` file, and another copy is sent to standard output. This allows for real-time viewing of aggregated logs while also persisting them. The script runs indefinitely until manually interrupted. The primary complexity lies in constructing the command string dynamically and handling potential errors like non-existent log files. Time complexity is effectively O(N*M) where N is the number of log files and M is the rate of log entries, as `tail -f` and `tee` are efficient I/O operations.

1. Define the output log file path and an array of input log file paths. 2. Define a helper function `_is_readable` that checks if a file exists and is readable. 3. Clear the output log file if it exists, or create it if...

This script safely traverses a directory, finds files matching a pattern, and processes each file individually. It uses `find -print0` to handle filenames with spaces or special characters and pipes the null-terminated o...

The script utilizes `find` with the `-print0` option to generate a null-terminated list of filenames. This is crucial for correctly handling filenames containing spaces, newlines, or other special characters. The output is piped to `xargs -0`, which reads the null-delimited input and executes the `process_file` function for each item. The `process_file` function itself is designed to be safe by quoting its argument. Error handling is included for invalid input directories and for cases where `process_file` might fail. The time complexity is roughly O(N*M) where N is the number of files and M is the average time to process a file, as `find` is efficient for directory traversal. Space complexity is O(1) beyond the storage for filenames passed to `xargs`.

1. Define a function `process_file` that takes a filename as input. 2. Inside `process_file`, validate if the input is a regular file. 3. If it's a file, perform some operation (e.g., count lines) and return success. 4....

This script ensures atomic updates to a configuration file. It first writes the new configuration to a temporary file. After validating the temporary file's content (e.g., syntax check), it creates a backup of the origin...

The script employs a robust strategy for atomic file updates. It begins by creating a temporary file (`.tmp_update.$$`) in the same directory as the target configuration file. This is crucial because `mv` operations are typically atomic when the source and destination are on the same filesystem. The new configuration content is written to this temporary file. A validation step (`_validate_config`) is performed on the temporary file to ensure its integrity. If validation passes, a backup of the original file is created using `cp`. The final step is an atomic `mv` command to replace the original configuration file with the temporary one. If the `mv` operation fails, the script attempts to restore the configuration from the backup. This multi-step process, especially the use of `mv` on the same filesystem, guarantees that the configuration file is either in its old state, its new state, or is being restored from backup, never in an intermediate, potentially corrupted state. Time complexity is dominated by file operations like `cat`, `echo`, `cp`, and `mv`, which are generally efficient, plus the validation step. Space complexity is O(N) where N is the size of the configuration file, due to the temporary file and backup.

1. Define constants for the configuration file path, temporary file suffix, and backup suffix. 2. Define a helper function `_validate_config` that takes a filename and returns success if the content is valid, failure oth...