Here's the sequel to my "
collection of small Unix utilities written in Ruby" post and
github repository.
Useful technique - Pathname
One thing I forgot to mention the last time -
Pathname library.
Pathname is an objects-oriented way to look at paths in a file system. A Pathname object is not the same as a
File or
Directory object since it's not opened - and might not even exist yet. It's also not like
String since it has all the filesystem awareness.
For very simple scripts it's fine to use just plain
Strings to represent filesystem paths, but once it gets a bit more complicated your script will get a lot more readable with
Pathname - and it costs you nothing.
Let's just look at
fix_permissions utility. Here's the core part:
class Pathname
def script?
read(2) == "#!"
end
def file_type
`file -b #{self.to_s.shellescape}`.chomp
end
def should_be_executable?
script? or file_type =~ /\b(Mach-O|executable)\b/
end
end
def fix_permissions(path)
Pathname(path).find do |fn|
next if fn.directory?
next if fn.symlink?
next unless fn.executable?
fn.chmod(0644) unless fn.should_be_executable?
end
end
Since
Pathname overloads
#to_str method it can be transparently used in most contexts where
String is expected - including printing it, file operations, system/exec commands and so on. You'll rarely need to use
#to_s - mostly when you want to regexp it.
I feel
Pathname#shellescape should exist, but since it doesn't that's one place where you need to use
.to_s.shellescape for now.
So what does this script do? First we add a few methods to
Pathname class. It already knows if something is a
directory?,
symlink?, and
executable? (that is - has +x flag).
We want to know if it is a script. And that's easy - just
read(2) as if it was a
File to read first two bytes. It looks much more elegant than
File.read(path, 2) != "#!" we'd need if we used
Strings - not to mention how
String class is really no place for
#script? method so we'd probably use a standalone procedure.
Next let's make
file_type method - and use
#shellescape to do it safely. Unfortunately that one is only defined on
Strings.
After that it's just one regexp away from
should_be_executable?.
Once we defined that notice how easy it is to dig into directory trees with
Pathname#find, and then just use a few
#query? methods to ask the path what it is about, then
#chmod to setup proper flags.
Other very useful methods not present in the script are
+ for adding relative paths,
#basename/
#dirname for splitting it into components, and
#relative_path_from for creating relative paths.
While I'm at it, use
URI objects for URIs you want to do something complicated with rather than regexping them - usually your code will look better too.
Individual commands
colcut
Cuts long lines to specific number of characters for easy previewing.
colcut 80 < file.xml
fix_permissions
Removes executable flag from files which shouldn't have it. Useful for archives that went through a Windows system, zip archive, or other system not aware of Unix executable flag.
It doesn't turn +x flag, only removes it if a file neither starts with #!, nor is an executable according to file utility.
Usage example:
fix_permissions ~/Downloads
If no parameters are passed, it fixes permissions in current directory.
progress
Display progress for piped file.
Usage examples:
cat /dev/urandom | progress | gzip >/dev/null
progress -l <file.txt | upload
By default it's in bytes mode. Use
-l to specify line mode.
If progress is piped a file and it's in byte mode, it checks its size and uses that to display relative progress (like
18628608/104857600 [17%]). Otherwise it will only display number of bytes/lines piped through.
You can also specify what counts as 100% explicitly:
progesss 123456
progress 128m
progress -l 42042
It will happily go over 100% on display.
since_soup
Link to soup posts starting from the post before one specified.
Usage example:
since_soup http://taw.soup.io/post/307955954/Image
sortby
Sort input through arbitrary Ruby expression. A lot more flexible than Unix
sort utility.
Usage example:
sortby '$_.length' <file.txt
Unless otherwise expressly stated, all original material of whatever nature created by Tomasz Węgrzanowski and included in this blog, is licensed under a Creative Commons License. It is also licensed under GFDL (for Wikipedia compatibility).
