I'm trying to get the hang of basic terminal commands in Linux, specifically focusing on redirection and copying files. I'm currently using Pop!_OS and learning from resources like Linux Journey. I've been stuck on a couple of things:
1. I'm confused about the use of redirection symbols (``). For example, if I run `cat banana.txt`, it seems to do the same thing as `cat peanuts.txt > banana.txt`. What's the difference, and why do we use `<`?
2. When I try to concatenate two text files using `cat fruits.txt`, it only takes the contents of `banana.txt` into `fruits.txt`. Why doesn't it work as I expect, combining both files?
3. Lastly, how can I copy a file in a directory where a file with the same name already exists, say copying `image1.jpg` to Downloads and renaming it to `image2.jpg`? The resources I've looked at haven't been very clear on this, and searching online has led to conflicting information.
3 Answers
There's actually a reason behind the behaviors you noticed with redirection! When you run `cat < peanuts.txt banana.txt`, it's important to note that redirection means the file (peanuts.txt) is being provided as stdin to `cat`. But `banana.txt` is being treated as a direct command line argument. Since `cat` sees that it has an argument, it prioritizes reading from that instead of stdin. Simply put, if you want to combine both files, you just stick by listing them both without redirection.
Regarding copying files: if you want to copy `image1.jpg` to a location where a file with the same name exists and rename it to `image2.jpg`, you’d use a command like `cp image1.jpg ~/Downloads/image2.jpg`. That's the way to go without overwriting the existing file!
Hey! If you want to copy or move a file ensuring it doesn't overwrite an existing file, you might want to look into the `cp -n` command to prevent overwriting. For example, `cp -n image1.jpg ~/Downloads/image2.jpg` will do exactly what you're asking for, copying it as `image2.jpg` without replacing the file that’s already there. Also, if you’re dealing with deeper directory paths and want to save some typing, consider using the Tab key for autocompletion. Just start typing your command, and when you get close, hit Tab to auto-complete that file path!
The redirection with `cat` can be a bit confusing at first. Essentially, both commands will yield the same output when you're just using `cat`. But using `<` means you're explicitly telling the shell to take input from a file instead of the keyboard. When you type `cat peanuts.txt`, you're directly opening that file with `cat`. But using `cat < peanuts.txt` shifts that responsibility to the shell, which opens `peanuts.txt` and feeds it to `cat` as if it were typed in the terminal.
For your second question, the reason `cat fruits.txt` behaves that way is that when you use ` fruits.txt`.
The example with stdin and arguments was super helpful! Appreciate the clarity!
Got it! That clears up a lot. Thanks for that explanation!