Diff patch output saved to a file. How to see it syntax-colored

colorsdiff()syntax highlighting

I have a folder with subfolders that contains text files.

Every now and then I run a script that makes a copy of that folder tree and then creates a new one with fresh info.

After that, having the old version and the new version, I run diff to know what changed between the old version and the new, sending the output to a file:

diff myFiler.old myFolder > diff_report.txt

The question is.

– How can I see diff_report.txt syntax colored?

I don't mean to see the actual output colored like git does when it uses diff, but use such syntax-coloring to see the diff output that has already been saved to a file.

Best Answer

Any decent editor is able to highlight diffs conveniently. You can generally persuade your editor by using the .diff extension, or by setting the filetype to diff otherwise.

It's called "paging output" or (somewhat erroneously) "pagination" …

… and man does it by invoking your preferred pager shell command, named by your PAGER environment variable, upon the output of whatever pipeline was used to generate the output form of the manual page. It falls back to a default if you haven't specified a pager command. On early Unices the default pager program, that man invokes as the default pager command with known hardwired options, was pg. On your system it is probably more or less. Some man commands look at other environment variables for pager commands, as well.

You do it by doing what man is doing: pipe the output of what you want to see into the standard input of a pager program.

You should get yourself a good book on Unix. There are a fair few that explain this, which is a very basic feature of the system. A simple Google Books search for pager unix more by me today turned up over a hundred books that discuss this. (I stopped counting at a hundred.)

How to pipe colored diff output to less

diff cannot output colors, you need another program, such as colordiff for that. Colors in the terminal are printed via ANSI escape codes which less does not interpret by default. To get less to correctly show colors, you need the -r, or even better, -R switch:

colordiff -- "$file1" "$file2" | less -R

From man less:

   -R or --RAW-CONTROL-CHARS
          Like -r, but only ANSI  "color"  escape  sequences  are
          output in "raw" form.  Unlike -r, the screen appearance
          is maintained correctly in most  cases.   ANSI  "color"
          escape sequences are sequences of the form:

               ESC [ ... m

          where  the  "..."  is  zero or more color specification
          characters For the purpose of keeping track  of  screen
          appearance,  ANSI color escape sequences are assumed to
          not move the cursor.  You  can  make  less  think  that
          characters  other  than  "m"  can end ANSI color escape
          sequences by setting the environment  variable  LESSAN‐
          SIENDCHARS  to  the  list of characters which can end a
          color escape sequence.  And you  can  make  less  think
          that characters other than the standard ones may appear
          between the ESC and the m by  setting  the  environment
          variable  LESSANSIMIDCHARS  to  the  list of characters
          which can appear.

Alternatively, you can use more which will display colors correctly by default.

If you cannot install external programs, you should be able to get the same output using a more manual approach:

diff a b | 
   perl -lpe 'if(/^</){$_ = "\e[1;31m$_\e[0m"} 
              elsif(/^>/){$_ = "\e[1;34m$_\e[0m"}'

Best Answer

Related Solutions

On Unix how to get the output from the diff command to look like a man page? Where I can press ‘b’ or ‘f’ to read further or back

It's called "paging output" or (somewhat erroneously) "pagination" …

How to pipe colored diff output to less

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