relink: Rewriting Symlinks with Perl

Fellow Monks,

I've just made the first public release of a tool I've been working on called relink (Update: it's GPLv3), and I wanted to tell you about it in the form of a short narrative, below. But first, just to whet your appetite:

  # Rewrite the targets of symlinks with Perl
$ relink rewrite 's/foo/bar/' PATH(s)
  # Convert between absolute and relative targets
$ relink abs2rel PATH(s)
$ relink rel2abs PATH(s)
  # List links  [only certain symlinks]
$ relink list [-t '/foo/'] PATH(s)
[download]

In this fictional scenario, let's say I've been keeping activity reports. I decided to keep weekly logs, but since I was supposed to file them monthly, and I wasn't very careful about which weeks I began and ended the reports on, I've ended up with this mishmash of files and symlinks:

~/Documents$ find . ! -type d -printf '%y %p\t%l\n'
f ./Reports Oct 2016/Report Weeks 40-42.xls    
f ./Reports Oct 2016/Report Weeks 43-46.xls    
l ./Reports Nov 2016/Report Weeks 43-46.xls    /home/foobar/Documents/
+Reports Oct 2016/Report Weeks 43-46.xls
f ./Reports Nov 2016/Report Weeks 47-51.xls    
l ./Reports Dec 2016/Report Weeks 47-51.xls    /home/foobar/Documents/
+Reports Nov 2016/Report Weeks 47-51.xls
[download]

Later, I realize that a different directory structure would make much more sense. No problem, I'll just do that by hand:

~/Documents$ mkdir 'Reports 2016'
~/Documents$ for M in Oct Nov Dec; do \
  mv -v "Reports $M 2016" "Reports 2016/$M"; done
‘Reports Oct 2016’ -> ‘Reports 2016/Oct’
‘Reports Nov 2016’ -> ‘Reports 2016/Nov’
‘Reports Dec 2016’ -> ‘Reports 2016/Dec’
~/Documents$ find . ! -type d -printf '%y %p\t%l\n'
f ./Reports 2016/Oct/Report Weeks 40-42.xls    
f ./Reports 2016/Oct/Report Weeks 43-46.xls    
l ./Reports 2016/Nov/Report Weeks 43-46.xls    /home/foobar/Documents/
+Reports Oct 2016/Report Weeks 43-46.xls
f ./Reports 2016/Nov/Report Weeks 47-51.xls    
l ./Reports 2016/Dec/Report Weeks 47-51.xls    /home/foobar/Documents/
+Reports Nov 2016/Report Weeks 47-51.xls
[download]

D'oh! Forgot about those symlinks, now they're broken! But no problem, relink to the rescue!

~/Documents$ relink rewrite 's{/Reports (\w+) 2016/}{/Reports 2016/$1/
+}'
~/Documents$ find . ! -type d -printf '%y %p\t%l\n'
f ./Reports 2016/Oct/Report Weeks 40-42.xls    
f ./Reports 2016/Oct/Report Weeks 43-46.xls    
l ./Reports 2016/Nov/Report Weeks 43-46.xls    /home/foobar/Documents/
+Reports 2016/Oct/Report Weeks 43-46.xls
f ./Reports 2016/Nov/Report Weeks 47-51.xls    
l ./Reports 2016/Dec/Report Weeks 47-51.xls    /home/foobar/Documents/
+Reports 2016/Nov/Report Weeks 47-51.xls
[download]

Fixed! But it'd be much nicer if those were just relative symlinks... no problem!

~/Documents$ relink abs2rel
~/Documents$ find . ! -type d -printf '%y %p\t%l\n'
f ./Reports 2016/Oct/Report Weeks 40-42.xls    
f ./Reports 2016/Oct/Report Weeks 43-46.xls    
l ./Reports 2016/Nov/Report Weeks 43-46.xls    ../Oct/Report Weeks 43-
+46.xls
f ./Reports 2016/Nov/Report Weeks 47-51.xls    
l ./Reports 2016/Dec/Report Weeks 47-51.xls    ../Nov/Report Weeks 47-
+51.xls
[download]

But wait! There's more!

relink can also:

Convert relative to absolute symlinks with the rel2abs command
Show you what it's doing (in color!) with the -v (verbose) option
Show you what it would do, without actually performing the operations, with the -n (dry-run) option
Resolve chains of symlinks to a certain depth, with the -d option
Limit its operations to broken symlinks or non-broken symlinks, with the options -b or -B respectively
Limit its operations on links for which a Perl expression returns true, with the -t CODE option, e.g. -t '/regex/' where $_ is the result of readlink on the link. For example, the following will list only those symlinks which are in ~/Documents and whose targets, when fully resolved, point to files also in the ~/Documents directory (the special variables $FULL and $PATHS are documented in the POD).
```
~$ relink list -t '$FULL=~/^$PATHS/' -- ~/Documents
/home/foobar/Documents/Reports 2016/Nov/Report Weeks 43-46.xls -> ../O
+ct/Report Weeks 43-46.xls
/home/foobar/Documents/Reports 2016/Dec/Report Weeks 47-51.xls -> ../N
+ov/Report Weeks 47-51.xls
[download]
```

Simply show you a (colorized) list of symlinks:

~/Documents$ relink list
./Reports 2016/Nov/Report Weeks 43-46.xls -> ../Oct/Report Weeks 43-46
+.xls
./Reports 2016/Dec/Report Weeks 47-51.xls -> ../Nov/Report Weeks 47-51
+.xls
[download]

And last but not least, it can walk chains of symlinks:

~$ relink list -l `which x-www-browser`
/usr/bin/x-www-browser -> /etc/alternatives/x-www-browser -> /usr/bin/
+firefox -> /usr/lib/firefox/firefox.sh
[download]

You can learn about all of the above features (and a few more!) from the POD, with perldoc relink.

Regards,
-- Hauke D

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