How to Setup a Fallback Font for Missing Glyphs in Terminus Font

You could use a different commandline tool, ttfdump, assuming you're looking at a TTF font file. It should also work for OTF fonts, if they belong to the TTF variety:

ttfdump /path/to/your/file.ttf  \
   | grep -E '(Number of Glyphs:|numGlyphs:|numberOfHMetrics:)'

This should get you the number of glyphs. You'll possibly see up to four different numbers, if the TTF is in some way b0rken. Sane TTF will return identical numbers for all three entries, in which case you may be pretty confident that you got the correct number:

ttfdump /Library/Fonts/WeidemannStd-Book.otf  \
  | grep -E '(Number of Glyphs:|numGlyphs:|numberOfHMetrics:)'

    numberOfHMetrics:      253
    numGlyphs:             253

Another example:

ttfdump /Library/Fonts/DroidSerif-Regular.ttf \
   | grep -E '(Number of Glyphs:|numGlyphs:|numberOfHMetrics:)'

     numberOfHMetrics:     609
     numGlyphs:            609
     numGlyphs:            609
     Number of Glyphs:     609

There is a simple solution that you can use. You will need Perl and libfont-ttf-perl package :

#! /usr/bin/perl 
use Font::TTF::Font; 

unless (defined $ARGV[0]) { 
    die <<'EOT'; 
    ttfnumglyphs infontfile ... 
Prints glyph count for each input TTF file 
EOT 
} 

foreach (@ARGV) { 
    $f = Font::TTF::Font->open($_) || die "Unable to open font file $_"; 
    $num = $f->{'maxp'}{'numGlyphs'}; 
    printf "%6d  %s\n", $num, $_; 
    $f->release; 
} 

The only thing you need to do is to save this script to a file, call it throught Perl and give it as a parameter the path of the font you want to count the glyphs :

$ perl glyphs_counter.pl /path/to/the/foo_font.ttf

It seems to work for TTF and OTF formats. Hope it helps.