tac:tldr:73231

tac: Use a specific regex as a separator.

$ tac --regex --separator ${[,;]} ${filename1 filename2 ---}

try on your machine

The command you provided:

tac --regex --separator ${[,;]} ${filename1 filename2 ---}

is a combination of options and arguments to the tac command.

tac: The tac command is used to concatenate and print files in reverse order. It reads the specified files from the end and prints them in reverse order.

Options:

--regex: This option tells tac to treat the separator as a regular expression instead of a simple string.
--separator ${[,;]}: This option specifies the separator pattern to use. In this case, it uses a regular expression to define the separator pattern. The pattern is ${[,;]}, which means it will treat either , or ; as the separator.

Arguments:

${filename1 filename2 ---}: These are the file names or file paths that you want to concatenate and print in reverse order. You can specify multiple file names separated by whitespace.

For example, if you have three files named "file1.txt", "file2.txt", and "file3.txt", executing the command:

tac --regex --separator ${[,;]} file1.txt file2.txt file3.txt

will read the contents of those files from the end and print them in reverse order based on the defined separator pattern.

This explanation was created by an AI. In most cases those are correct. But please always be careful and never run a command you are not sure if it is safe.

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