How to monitor file concatenation progress?

To monitor the progress of file concatenation in Linux, you can use the pv (Pipe Viewer) command. This tool allows you to see the progress of data through a pipeline. Here’s how you can use it with the cat command:

Install pv: If you don't have pv installed, you can install it using your package manager. For example, on Debian-based systems, you can use:
```
sudo apt-get install pv
```
Use pv with cat: You can pipe the output of cat through pv to monitor the progress. Here’s the command:
```
cat file1.txt file2.txt | pv -s $(du -b file1.txt file2.txt | awk '{sum += $1} END {print sum}') > combined_file.txt
```
In this command:
- du -b file1.txt file2.txt calculates the total size of the files in bytes.
- awk sums the sizes to provide a total size to pv using the -s option.
- pv will then display the progress of the concatenation.
Alternative with dd: If you prefer, you can also use dd with pv to concatenate files while monitoring progress:
```
pv file1.txt file2.txt | dd of=combined_file.txt
```

Using pv in this way will give you a visual indication of how much data has been processed and how much is left, making it easier to monitor the progress of concatenating large files.