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Tag: sed

Remove appending slash from a path using Sed

Here’s how you can remove the appending slash from a path using sed, the stream editor:

/just/a/path/ | sed -e 's#/$##'
# Output: /just/a/path
# And, if there isn't an appending slash, nothing happens:
 /just/another/path | sed -e 's#/$##'
# Output: /just/another/path 

It works quite simple. Sed executes expression (-e) on its standard input. The expression is a substitution using regular expressions. The #-sign is the delimiter. The part (#/) between the first two hash signs is the matching expression and the (empty) part between the second and the third hash sign is the replacement expression. This expression (“s#/$##”) basically says: replace all occurrences of “/” at the end of the line (the dollar sign is the end-of-line anchor) with nothing.

To use this in a script is easy-peasy. Suppose $1 is a system path that may or may not include an appending slash:

sanitized_path= "$1" | sed -e 's#/$##'`

This script outputs its first parameter with the appending slash removed.

Styling XML SVN logs with CSS

My friend, Wiebe, keeps his website in Subversion. (Always keep your project files in version management or you’ll be sorry.) He used to manually track the date with the last significant change in each file (because who cares about typos, right?). But, of course, he kept forgetting to update this when he actually made such changes. So, he decided that he wanted to publish the full SVN log for each page.

The raw SVN logs are a bit raw, reason enough to try to turn it in something prettier. Luckily, there’s no need to parse the log files, because svn log has a command-line option, --xml. This option causes the log file to be printed in a simple XML format:

<?xml version="1.0"?>
<logentry revision="345">
<msg>Added very useful note to index about an awkward sentence.
<!-- Snipped the rest of the logentry elements -->

Now we can use any number of ready-to-use XML tools to process this log, but I figured that, maybe, a very simple solution could work: CSS. Cascasing Stylesheets can be used for more than just styling HTML. One of the few differences is that with non-HTML XML, there are no defaults for the CSS properties (and aren’t we always trying to discover and override the various browser-specific CSS defaults anyway?)

First, we want to add a <?xml-stylesheet?> processing instruction to the log file:

svn log --xml example_file.xhtml | sed -e '/<\?xml / a<?xml-stylesheet type="text/css" media="screen" href="/css/svn-log.css"?>'

The XML file now references the CSS file that we’re going to make:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/css" media="screen" href="svn-log.css"?>
<!-- snip -->


log {
 : 2em 204px 2em 5ex;
logentry {
 : 1em;
 : #999;
author {
date {
 : 10ex;
  /* If Firefox would support font families even when you force a font,
     I could use 'overflow: hidden' to hide everything except the date part of <date>. */
 : 110%;
 : #7488a7;
msg {
 : pre-wrap;

We now have a nicely formatted log file. Other things you could do:

  • Add styles for printing (in a separate stylesheet or by using @media blocks).
  • Display the revision author instead of hiding it.

Of course, you could do all this and much more with XSLT, but that’s just all too obvious. 🙂

If you want to see the stylesheet in action, take a look at Wiebe’s website and look for a View revision log of this page link in the footer of any of his pages.

XML SVN log styled with CSS

XML SVN log styled with CSS

Wget one-liner

Earlier today, I wanted to download all songs by this totally kick-ass rap outfit:

wget -q -O - \
| sed --quiet -e 's#^.*<a href="\(nummers/.*\.mp3\).*$#\1#p' \
| sort -u \
| wget -i - -B ''

The same command-line, now using GNU long options to increase readability:

wget --quiet --output-document=- \
| sed --quiet --expression='s#^.*<a href="\(nummers/.*\.mp3\).*$#\1#p' \
| sort --unique \
| wget --input-file=- --base=''

Using wget to download all files on a page

Just a quick one-liner I used to download a bunch of MIDI files from an on-line listing of Chopin MIDIs:

$ wget -q -O - \
| grep 'href=".*\.mid"' \
| sed -e 's/^.*href="\(.*\)".*$/\1/' \
| xargs -i{} wget{}

Maybe not so useful to you, but it’s a good demonstration of applying the hacker’s mentality to one of those moments where, after clicking the fourth link or so, I find myself thinking: Wouldn’t spending a few moments on a one-liner be much more fun than clicking through and saving 44 more links?

Useful or not, I am now testing timidity’s piano sound with a nice rendition of Chopin in the background whereas, without this trick, I’d still be right-click-click-saving links instead of writing this post. It’s up to you to decide whether this is actually good or bad. 😛

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