Overview
The rev command is a utility that reverses the order of characters in every line of the input text, moving the end of the line to the start. This tool is frequently utilized in combination with other commands for log analysis based on specific suffixes, data integrity verification, or as a general aid in string manipulation.
Specifications (Arguments and Options)
Syntax
BASH
rev [file_name]
Main Arguments
| Argument | Description |
| file_name | Specifies the text file to be processed. If omitted, the command reads from standard input. |
Basic Usage
In this scenario, a system administrator named mori needs to reverse the lines of a text file to verify configuration values for a specific project.
BASH
# Create a sample file in the workspace
echo "mori_project_2026" > /home/mori/workspace/sample.txt
echo "linux_system_admin" >> /home/mori/workspace/sample.txt
# Execute reversal with the rev command
rev /home/mori/workspace/sample.txt
TEXT
6202_tcejorp_irom
nimda_metsys_xunil
Practical Command Scenarios
This example demonstrates a pipeline where line numbers are added, the content is reversed, and the vertical order of the lines is inverted, moving the last line to the top of the output.
BASH
# Add line numbers, reverse character order, and use tac to invert the vertical line order
cat -n /home/mori/workspace/build_task.log | rev | tac
TEXT
gol.ksat_dliub/ecapskrow/irom/emoh/ 2
txet.elpmas/ecapskrow/irom/emoh/ 1
Customization Points
The file path /home/mori/workspace/build_task.log should be replaced with the absolute path of the specific log file or list intended for analysis. If line numbers are unnecessary, the cat -n command can be removed. Similarly, the tac command should be excluded if reversing the vertical line order is not required for the specific task. When processing the output of another command directly, the format command | rev should be used to provide the input.
Important Notes
Multi-byte characters, such as those used in Japanese, may not be reversed correctly depending on the system’s locale settings. It is essential to verify operations in a UTF-8 environment to avoid text corruption or unexpected displays. It is also important to distinguish rev from the tac command; rev flips characters horizontally (character order), while tac flips lines vertically (line order). Finally, the line feed character at the end of each line remains unaffected by the reversal, ensuring the overall line structure is preserved.
Advanced Applications
A common technique for extracting file extensions from a path involves reversing the entire string, cutting the first field delimited by a dot, and then reversing the result back to its original direction.
BASH
# Reverse the path, extract the first field (the extension), and reverse it back
echo "/home/mori/backup/config.tar.gz" | rev | cut -d'.' -f1 | rev
TEXT
gz
Summary
The rev command proves most effective when used as a filter within a pipeline rather than as a standalone tool. By combining it with line numbering or vertical inversion, administrators can perform complex string operations that are difficult to achieve with standard commands alone. Accurate system administration requires a clear understanding of the distinction between horizontal reversal and vertical inversion while ensuring that data encoding is compatible with the environment. Utilizing this tool allows for precise extraction of specific string elements, such as file extensions, through efficient character manipulation.
