How to use the command rargs (with examples)

The rargs command is a tool that allows you to execute a command for each line of standard input, similar to the xargs command. However, it also provides pattern matching support, which makes it more versatile. This article will provide examples of different use cases of the rargs command.

Use case 1: Execute a command for every line of input

Code:

command | rargs command {0}

Motivation: In some cases, you may have a command that requires input from multiple lines, and you want to process each line individually. The rargs command allows you to do that by executing a command for every line of input. The {0} in the command is a placeholder for the current line of input.

Explanation:

• command: The command you want to execute for each line of input.
• {0}: A placeholder that will be replaced with each line of input.

Example output: If we have a file input.txt with the following content:

apple
banana
orange

And we run the command: cat input.txt | rargs echo "I like {0}."

The output will be:

I like apple.
I like banana.
I like orange.

Use case 2: Do a dry run

Code:

command | rargs -e command {0}

Motivation: Sometimes you may want to see the commands that would be run without actually executing them. This can be useful for testing or troubleshooting purposes. The -e option enables the dry run mode.

Explanation:

• -e: Enables the dry run mode, which prints the commands that would be run instead of executing them.

Example output: If we have a file input.txt with the following content:

file1.txt
file2.txt
file3.txt

And we run the command: cat input.txt | rargs -e mv {0} {0}.bak

The output will be:

mv file1.txt file1.txt.bak
mv file2.txt file2.txt.bak
mv file3.txt file3.txt.bak

Use case 3: Remove the .bak extension from every file in a list

Code:

command | rargs -p '(.*).bak mv {0} {1}

Motivation: There may be situations where you need to rename a set of files by removing a specific extension. The -p option allows you to use pattern matching to manipulate the input.

Explanation:

• -p '(.*).bak: Uses regular expression pattern matching to match the input lines that end with .bak.
• mv {0} {1}: Renames the file by removing the .bak extension. {0} represents the original file name, and {1} represents the new file name.

Example output: If we have a file input.txt with the following content:

file1.txt.bak
file2.txt.bak
file3.txt.bak

And we run the command: cat input.txt | rargs -p '(.*).bak mv {0} {1}

The output will be:

mv file1.txt.bak file1.txt
mv file2.txt.bak file2.txt
mv file3.txt.bak file3.txt

Use case 4: Execute commands in parallel

Code:

command | rargs -w max-procs

Motivation: In certain scenarios, you may want to execute commands in parallel to improve efficiency. The -w max-procs option allows you to specify the maximum number of processes to run concurrently.

Explanation:

• -w max-procs: Sets the maximum number of processes to run concurrently. max-procs can be replaced with an integer value to define the specific number of processes to run in parallel.

Example output: If we have a file input.txt with the following content:

1
2
3

And we run the command: cat input.txt | rargs -w 2 sleep {0}

The output will be:

(No output will be displayed as it runs in the background)

However, in this example, the sleep command is executed in parallel for each line of input, with a maximum of 2 processes running concurrently.

Use case 5: Consider each line of input to be separated by a NUL character instead of a newline

Code:

command | rargs -0 command {0}

Motivation: By default, the rargs command treats each line of input as separated by a newline character (\n). However, in some cases, you may have input where lines are separated by different characters. The -0 option allows you to specify the delimiter character (\0).

Explanation:

• -0: Considers each line of input to be separated by a NUL character (\0) instead of a newline (\n).

Example output: If we have a file input.txt with the following content:

apple\0banana\0orange

And we run the command: cat input.txt | rargs -0 echo {0}

The output will be:

apple
banana
orange

Conclusion:

The rargs command is a powerful tool that allows you to process each line of standard input by executing a command. Its pattern matching support and additional options make it a versatile alternative to the xargs command. By using examples of different use cases, this article has shown how rargs can be used to perform various tasks with ease and flexibility. Whether you need to execute commands in parallel, manipulate file names, or handle input lines with different delimiters, rargs can be a valuable addition to your command-line toolkit.