Exploring the Command 'xe' for Line-by-Line Execution (with examples)

The xe command is a powerful tool for executing a specified command once for each line of input data that is piped from another command or sourced from a file. It is particularly advantageous when handling batch operations where each line signifies a separate task or input parameter. This command simplifies scenarios where repetitive execution of a similar process across multiple data entries is required.

Run a command once for each line of input data as arguments

Code:

arguments_source | xe command

Motivation:

Using xe in this manner is beneficial when you need to apply the same shell command or utility across multiple data inputs. Each line of the input serves as the argument for the command. This can significantly automate tasks such as batch processing user inputs, iterating over a list of URLs for curl operations, or processing file paths for conversion operations in a systematic manner.

Explanation:

• arguments_source: Represents the command or file that generates the input lines.
• |: A pipe that passes the output of arguments_source as input to xe.
• xe: Executes the specified command once for each line from arguments_source.
• command: The command to be executed with each line of input as its argument.

Example output:

If you have a file names.txt containing:

John
Doe
Jane
Smith

And you execute:

cat names.txt | xe echo

The output would be:

John
Doe
Jane
Smith

Execute the commands, replacing any occurrence of the placeholder (marked as {}) with the input line

Code:

arguments_source | xe command {} optional_extra_arguments

Motivation:

This usage is incredibly handy when you want to include the input line dynamically within your command string, allowing for more flexibility and customization of the execution behavior. You might need this, for instance, when constructing URLs, forming complex queries, or tailoring terminal commands to each input entry.

Explanation:

• {}: A placeholder substituted by the current input line when the command is run.
• optional_extra_arguments: Any additional arguments required by the command besides the placeholder.

Example output:

With a list containing:

image1.png
image2.png
image3.png

Running:

cat images.txt | xe mv {} {}.backup

Will produce a command that renames each image file to its .backup version.

Execute a shellscript, joining every N lines into a single call

Code:

echo -e 'a\nb' | xe -N2 -s 'echo $2 $1'

Motivation:

In scenarios where pairs or groups of lines are relevant for the logic being executed, this approach enables you to process every N lines together rather than treating them individually. Ideal for working with datasets that are logically grouped, such as paired coordinates, key-value pairs, or other types of concatenated data.

Explanation:

• -N2: Determines that xe should combine every two lines for execution.
• -s 'echo $2 $1': A shellscript executed for every pair of lines, where $1 and $2 represent the individual lines within the pair.

Example output:

For the data:

a
b

The command:

echo -e 'a\nb' | xe -N2 -s 'echo $2 $1'

Yields:

b a

Delete all files with a .backup extension

Code:

find . -name '*.backup' | xe rm -v

Motivation:

Automating file management tasks like deleting unnecessary backup files across directories is essential for maintaining a clean and organized file system. The xe command assists in efficiently executing such file operations over a list of files, ensuring accuracy and speed.

Explanation:

• find . -name '*.backup': Generates a list of files ending with .backup.
• |: Pipes the file list to xe.
• xe rm -v: Executes the rm -v command for each file entry, where -v stands for verbose, providing information on each file deletion.

Example output:

If there are files file1.backup and file2.backup in the directory, the output will be:

removed 'file1.backup'
removed 'file2.backup'

Run up to max-jobs processes in parallel

Code:

arguments_source | xe -j max-jobs command

Motivation:

Leverage the power of parallel processing to fast-track operations and fully utilize the computational capacity of your system. This is particularly useful for time-consuming processes such as data processing, network operations, or handling I/O-bound tasks that can benefit from concurrent execution.

Explanation:

• -j max-jobs: Specifies the number of processes to run in parallel. max-jobs can be set based on system resources, where 0 defaults to using as many processes as there are CPU cores.
• command: The command to be executed concurrently per line of input.

Example output:

Consider the same list of URLs in urls.txt. To download them using curl, and depending on your CPU, executing:

cat urls.txt | xe -j 4 curl -O

Would run up to 4 simultaneous curl processes, downloading multiple URLs concurrently, thus optimizing the task’s performance.

Conclusion:

The xe command serves as a robust tool for line-by-line execution of commands, offering versatile methods to leverage Unix pipelines efficiently. Its numerous features — from handling dynamic placeholders, processing line groups, to managing parallel executions — make it an essential utility for developers, system administrators, or anyone involved in scripting and batch processing tasks.