Hi, sorry about that, here is my branch where you can test my solution.

I have used macros defined in "/bin/convolve/ui.h" and "/bin/convolve/convolve.h", near the beginning of the files, to format strings with the necessary ANSI escape sequences for color printing as well as checking if stdout is a file or a tty.

You can see examples of the usage at "/bin/convolve/ui.c" L707 to L711, L813 and "/bin/convolve/convolve.c" L843

Presumably if we were to follow this approach, you would need a single header containing all the color macros that can be included wherever required.

Additionally, if we want to give the user a choice over whether color should be used, either the macro would be modified or we could also use static functions for the same.

I have included a script(color-test.sh) to test this. Do let me know your thoughts and any changes that need to be done.

chmod +x color-test.sh
./color-test.sh
./color-test.sh > temp.txt && cat temp.txt

Hi, I was working on this task and was able to get a basic implementation working for the verify option of astfits at my fork

I was wondering how this maybe generalized for the entire gnuastro and if there is some existing implementation I could refer to

ls from GNU Coreutils was not so helpful in this regard
Maybe some sort of module that provided functions to set the color of terminal output? and a command line flag to indicate color printing?

Hi! I tried to color code the various outputs by creating functions of different colors that switch the output color.
For example :

void red(){
printf("\033[1;31m");
}

void yellow(){
printf("\033[1;33m");
}

Then before printing the desired output we can simply call one of these to activate the desired output color. Now to check that the output is printed on terminal and not being piped we can use the "isatty(1)" function where "1" is the parameter that checks that stdout is on terminal.
For example in the  -- verify option in the fits program:

+static int
+keywords_verify(struct fitsparams p, fitsfile *fptr)
+{
+  int dataok, hduok, status=0;
+
+  /* Ask CFITSIO to verify the two keywords. */
+  if( fits_verify_chksum(*fptr, &dataok, &hduok, &status) )
+    gal_fits_io_error(status, NULL);
+
+  /*Applying a check to see that output is being printed on terminal itself */
+  if(isatty(1)){
+    /* calling the desired color function */
+    red();
+  }
+
+  /* Print the verification result. */
+  printf("DATASUM:  %s\n", ( dataok==1
+                             ? "Verified"
+                             : ( dataok==0 ? "NOT-PRESENT" : "INCORRECT" )));
+  printf("CHECKSUM: %s\n", ( hduok==1
+                             ? "Verified"
+                             : ( hduok==0  ? "NOT-PRESENT" : "INCORRECT" )));
+
+  /* Some further information. */
+  if(!p->cp.quiet)
+    printf("\n--------\n"
+           " - DATASUM:  calculated only from the HDU/extension's data (not "
+           "keywords).\n"
+           " - CHECKSUM: calculated from the full header (data and "
+           "keywords).\n\n");
+
+  /* Return failure if any of the keywords are not verified. */
+  return (dataok==-1 || hduok==-1) ? EXIT_FAILURE : EXIT_SUCCESS;
+}

will this work for the issue ? Please give suggestions :)

In many scenarios of Gnuastro's programs, it can be really helpful if the output text (on the command-line) is color coded. For example the new `--verify' option to the Fits program.

Fortunately all modern terminal emulators (even on Windows), follow the same ANSI escape codes to define colors (summary, or full Wikipedia description.

So the job isn't too hard, it just needs some checks (to remove when the output isn't being directly printed on a terminal, for example being piped). We should look to see how `ls' (in GNU Coreutils) does it.