Overview
Tac, with a name that is 'cat' spelled backward, outputs file content line by line in reverse order. By default, it uses newline characters as delimiters, but you can also specify other delimiters to process records in reverse.
Key Features
- Outputs file content line by line in reverse order
- Useful for checking the latest data, such as in log files
- Allows specifying custom delimiters (strings or regular expressions)
Key Options
Output and Delimiter Control
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Description:
`tac` Executes the command.
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Usage Examples
Output file content in reverse
tac access.logOutputs the content of the specified file in reverse order, from the last line to the first.
Using with pipes
cat file.txt | tacPasses the output of another command to tac for reverse processing.
Output in reverse using a specific string as a separator
echo 'apple::banana::cherry' | tac -s '::'Outputs content in reverse order using '::' as the record separator instead of newline characters.
Output in reverse using a regex separator
echo '1 one\n2 two\n3 three' | tac -r -s '[0-9] 'Outputs content in reverse order using a space following a digit as a regular expression separator.
Tips & Precautions
The tac command can increase memory usage when dealing with large files, so caution is advised. For processing large files, consider using other tools like `tail -r` (GNU tail) or `sed`.
Usage Tips
- Log File Analysis: By checking from the latest logs, you can reduce the time for problem diagnosis.
- Pipeline Utilization: You can pass the output of other commands to tac for reverse processing.
- Caution with Large Files: Since the entire file might be loaded into memory, it may not be suitable for very large files.