rev - macOS

Overview

rev reverses the lines of a file, or standard input if no file is specified. It’s often used for displaying text upside-down or in reverse chronological order.

Syntax

rev [options] [file]

Options/Flags

-h, –help : Display help and usage information.
-n, –number-lines : Prefix each reversed line with its original line number.
-s, –squeeze-blank : Remove empty lines from the output.

Examples

Display a file’s contents in reverse:
```
rev filename
```
Reverse lines and add line numbers:
```
rev -n filename
```
Reverse lines and remove empty lines:
```
rev -s filename
```
Reverse standard input:
```
echo "Hello World" | rev
```

Common Issues

File not found : Ensure the specified file path is valid.
Permission denied : Check if you have read access to the specified file.
Lines not reversed correctly : Verify that the input file doesn’t contain any non-text characters.

Integration

rev can be used with other commands for advanced tasks, such as:

head to display the first few lines of a reversed file:
```
rev filename | head -5
```
tail to display the last few lines of a reversed file:
```
rev filename | tail -5
```
sort to sort lines of a reversed file in reverse alphabetical order:
```
rev filename | sort -r
```

tac : Another command that reverses lines of a file.
fold : Wraps long lines of text.
fmt : Formats text files.