Ubuntu – How to diff the output of two commands

command linediff()

I had imagined the simplest way to compare the contents of two similar directories would be something like

diff `ls old` `ls new`

But I see why this doesn't work; diff is being handed a big long list of files on the command line, rather than two streams like I had hoped. How do I pass the two outputs to diff directly?

Best Answer

Command substitution `…` substitutes the output of the command into the command line, so diff sees the list of files in both directories as arguments. What you want is for diff to see two file names on its command line, and have the contents of these files be the directory listings. That's what process substitution does.

diff <(ls old) <(ls new)

The arguments to diff will look like /dev/fd/3 and /dev/fd/4: they are file descriptors corresponding to two pipes created by bash. When diff opens these files, it'll be connected to the read side of each pipe. The write side of each pipe is connected to the ls command.

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Ubuntu – How to diff two folders to multiple patch files

You can use the original format that creates the huge diff file which you can subsequently split into the small files. You might be interested in csplit for the splitting, or you can use a scripting language like Perl:

perl -ne 'if(/^diff -drupN (.*) (.*)/) {
              my $f = $1;
              $f =~ s{/}{_}g;
              open $FH, ">", "$f.patch" or die $!;
          } else {
              print {$FH} $_;
          }' kernel.patch

If you need the diff line in each file, add the print after the open.

Ubuntu – Get binary delta-encoded recursive diff of two directories as single patch file in CLI (and online use)

I would go for a low key solution. If I get you correctly, you want to update web pages and don't expect most of them changing, in which case I would just upload the changed files, whole.

This could be achieved eg. in mc, connect one panel over FTP to your web host, let other panel show the local version. Then select everything and copy, and choose to overwrite only all newer files (you can chose that for all files at once). Or use another file manager's synchronize facility, I believe krusader has some. Unless you've got big files which change only locally (what are they? databases¹? executables maybe, but not compressed?), binary deltas won't give you much IMO.

NOTE 1: Synchronizing databases in this way is a bad idea.

Best Answer

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Ubuntu – How to diff two folders to multiple patch files

Ubuntu – Get binary delta-encoded recursive diff of two directories as single patch file in CLI (and online use)

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