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> Use this file to discover all available pages before exploring further.

# Reading a Single Line from a File from the Command Line Interface



When you get an error report from a linter, interpreter, or compiler, you'll get results that tell you to look at a certain line number. You can then jump to that line in your editor or IDE. But sometimes it's nice to be able to just look at a single line in a file.

There are a number of ways to do this, but the shortest and fastest way (read: least amount of typing) is with the `sed` command, and its `-n` option:

```command
sed -n [line_number]p filename.txt
```

For example, to read the fifth line from a file called `index.html`, use  this command:

```command
sed -n 5p index.html
```

You can also use this to pipe data in. To view the second line of a long directory listing, you can do this:

```command
ls -alh | sed -n 5p
```

There are other solutions for this, but this solution is less typing. However, you can reduce the typing even more if you use a shell function.

If you're using Bash, you can add a function to your `~/.bash_rc` file on Linux/WSL or to `~/.bash_profile` on macOS that calls `sed`:

```bash
catln() {
  sed -n ${1}p ${2}
}
```

This function accepts two arguments: a line number and a file. To read line 5 of `index.html`, you call the function like this:

```command
catln 5 index.html
```

To use this, add this function to your appropriate profile file and then open a new terminal so it loads in or use `source` to load your configuration.

If you want to be able to pipe text into the function like you could with `sed`, you'll have to modify the function to read from standard input if you don't see the second argument. Here's how you'd do it:


```bash
catln() {
  num=$1
  input=$2
  if [ -z "$input" ]; then
    sed -n ${num}p </dev/stdin
  else
    sed -n ${num}p $input
  fi
}
```

For clarity, create two local variables: `num` to hold the number of lines, and `input` to hold the input. Then check to see if there was any input supplied. If it wasn't, then call `sed` and pass in `/dev/stdin` instead. Otherwise, pass the file.

Update the function in your profile file, source it or open a new terminal, and use the function with a pipe:

```command
ls -alh | catln 2
```

You'll see the second line of your directory listing.

## Conclusion

You now have a quick way to display a line from a file.