Open the lastest downloaded file with bash script - linux

Question

Below is my attempt at this problem. It's a functional script, but I have to specify the application to be used for each file type. Since this information regarding default application must be stored somewhere on Linux / Ubuntu already, how may I access them and incorporate into my script?
Also, can my script be more "elegant" in any way?
Thank you for helping a Bash script beginner! I appreciate any comment.
#!/bin/bash
# Open the latest file in ~/Downloads
filename=$(ls -t ~/Downloads | head -1)
filetype=$(echo -n $filename | tail -c -3)
if [ $filetype == "txt" ]; then
leafpad ~/Downloads/$filename
elif [ $filetype == "pdf" ]; then
evince ~/Downloads/$filename
fi

Answer 1

How do I open a file in its default program - Linux should help you with the first part of your question:
xdg-open ~/Downloads/$filename
As mentioned in other answers, it's best not to trust the output of ls in scripts, especially if you have unusual characters like newlines in your filenames. One way to robustly get a list of filenames in a script is with the find command, and null-delimiting them into a pipe.
So to answer your question with a one-liner:
find ~/Downloads -maxdepth 1 -type f -printf "%C# %p\0" | sort -zrn | { read -d '' ts file; xdg-open "$file"; }
Breaking it down:
The find command lists files in the ~/Download directory, but doesn't descend any deeper into subdirectories. The filenames are printed with the given printf format, which lists a numerical timestamp, followed by a space, followed by a null delimiter. Note the printf format specifiers for find are different to those for regular printf
The sort command numerically sorts (-n) the resulting null-delimited list (-z) by the first field (numerical timestamp). Sort order is reversed (-r) so that the latest entry is displayed first
The read command reads the timestamp and filename of the first file in the list into the ts and file variables. -d '' tells read to use null delimiters.
The file is opened using xdg-open.
Note the read and xdg-open commands are in a curly bracket inline group, so the file variable is in scope for both.

Answer 2

Welcome to bash programming. :-)
First off, I'll refer you to the Bash FAQ. Great resource, lots of tips, perspectives and warnings.
One of them is the classic Parsing LS problem that your script suffers from. The basic idea is that you don't want to trust the output of the ls command, because special characters like spaces and control characters may be represented in a way that doesn't allow you to refer to the file.
You're opening the "last" file, as determined by a sort that the ls command is doing. In order to detect the most recent file without ls, we'll need some extra code. For example:
#!/bin/sh
last=0
for filename in ~/Downloads/*; do
when=$(stat -c '%Y' "$filename")
if [ $when -gt $last ]; then
last=$when
to_open="$filename"
fi
done
xdg-open "$to_open"
The idea is that we'll walk through each file in your Downloads directory and fine the one with the largest timestamp using the stat command. Then open that file using xdg-open, which may already be installed on your system because it's part of a tool set that's a dependency for a number of other applications.
If you don't have xdg-open, you can probably install it from the xdg-utils package which using whatever package management system is around for your Linux distro.
Another possibility is gnome-open, which is part of the Gnome desktop (the libgnome package, to be precise). YMMV. We'd need to know more about your distro and your desktop environment to come up with better advice.
Note that if you do want to continue selecting your application by extension, you might want to consider using a switch instead of a series of ifs:
...
case "${filename##*.}" in
txt)
leafpad "$filename"
;;
pdf)
xdg-open "$filename"
;;
*)
echo "ERROR: can't open '$filename'" >&2
;;
esac

Answer 3

mimeopen might be useful? There's an explanation of Mime types here.
Also - are your filetype extensions always exactly two letters, as the tail -c -3 implies? If they're of variable length, you may want a regular expression instead.

Answer 4

As previously mentioned, xdg-open and mimeopen may be useful and more elegant; from their manpages:
xdg-open opens a file or URL in the user's preferred application. If a URL is provided the URL will be opened in the user's preferred web browser. If a file is provided the file will be opened in the preferred application for files of that type.
[mimeopen] tries to determine the mimetype of a file and open it with the default desktop application. If no default application is configured the user is prompted with an "open with" menu in the terminal.
For more elegance in the original script, replace
filetype=$(echo -n $filename | tail -c -3)
with
filetype=${filename: -3}
and instead of the five-lines if/elif/fi structure, consider using two lines as follows.
[ $filetype == "txt" ] && leafpad ~/Downloads/$filename
[ $filetype == "pdf" ] && evince ~/Downloads/$filename