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tac

Print files in reverse line order

TLDR

Reverse lines of a file
$ tac [file.txt]
Reverse lines from multiple files
$ tac [file1.txt] [file2.txt]
Reverse with custom separator
$ tac -s "[separator]" [file.txt]
Reverse with regex separator
$ tac -r -s "[pattern]" [file.txt]
Reverse stdin
$ cat [file.txt] | tac
Reverse before separator (attach separator to following)
$ tac -b -s "[separator]" [file.txt]

SYNOPSIS

tac [options] [file...]

DESCRIPTION

tac concatenates and prints files in reverse, line by line. The name is "cat" spelled backwards, reflecting its reversed functionality.By default, tac uses newline as the record separator, reversing line order. Custom separators can be specified, making it useful for reversing records in various file formats.The tool is handy for viewing log files (newest first), reversing sorted output, or processing data that needs to be in reverse order.

PARAMETERS

-b, --before

Attach separator before instead of after record.
-r, --regex
Interpret separator as regular expression.
-s string, --separator= string
Use string as separator instead of newline.
--help
Display help information.
--version
Display version information.

INSTALL

sudo apt install coreutils
sudo dnf install coreutils
sudo pacman -S coreutils
sudo apk add coreutils
sudo zypper install coreutils
brew install coreutils
nix profile install nixpkgs#coreutils

CAVEATS

Reads entire input into memory (inefficient for very large files). Binary files may produce unexpected results. Regex separators may have performance impact. Does not reverse characters within lines.

HISTORY

tac is part of GNU coreutils, following the Unix tradition of tools that reverse operations (like rev which reverses characters). The name playfully reverses "cat". It provides functionality not available in standard Unix, though some BSD systems have alternatives.

SEE ALSO

cat(1), rev(1), tail(1), head(1)