Inspect a Ppmdfont File with ppmddumpfont

You will finish with a readable diagnostic dump of a Netpbm Ppmdfont file, saved separately from normal command output. The examples use Netpbm 11.5.2, provided by Debian package netpbm version 2:11.05.02-1.1build1 on this machine.

Allow about ten minutes. You need a shell, the ppmddumpfont command, and a readable Ppmdfont file. This guide only reads the font and writes a report. It does not install a font, change Netpbm configuration or alter the input.

1. Confirm what the command accepts

ppmddumpfont has no filename argument and no options. It reads one Ppmdfont file from standard input and writes a human-readable description to standard error. That direction is the detail most likely to cause a confusing empty output file.

Check the installed version before relying on a copied example:

$ ppmddumpfont --version
ppmddumpfont: Using libnetpbm from Netpbm Version: Netpbm 11.5.2
ppmddumpfont: Built from source dated 2024-03-31 09:09:47
ppmddumpfont: Built by Debian

The command prints version information, but the installed manual documents no general command-line options. Do not add a path after the command and expect it to be opened as a file.

2. Locate a Ppmdfont file

A Ppmdfont file is a Netpbm drawing font, not a normal desktop font such as TrueType or OpenType. Netpbm documentation describes the usual filename suffix as .ppmdfont and the first eight bytes as the ASCII text ppmdfont. Search only the directories relevant to your work:

$ find /path/to/font-directory -type f -name '*.ppmdfont' -print

Replace /path/to/font-directory with a real directory. If the search returns nothing, you can create Netpbm's standard example font in a temporary directory:

$ workdir=$(mktemp -d /tmp/ppmddumpfont-XXXXXX)
$ ppmdmkfont > "$workdir/standard.ppmdfont"
$ wc -c "$workdir/standard.ppmdfont"
3899 /tmp/ppmddumpfont-XXXXXX/standard.ppmdfont

The exact temporary directory name will differ. ppmdmkfont takes no input and always generates the standard Ppmdfont data, so it is useful for a repeatable smoke test.

$ test -r "$workdir/standard.ppmdfont" && echo readable
readable

3. Dump the font and capture standard error

Feed the file through standard input. Redirect standard error to a report file, and leave standard output redirected separately so the two channels remain unambiguous:

$ ppmddumpfont < "$workdir/standard.ppmdfont" > "$workdir/stdout" 2> "$workdir/font-report.txt"
$ printf 'exit status: %s\n' "$?"
exit status: 0
$ wc -c "$workdir/stdout" "$workdir/font-report.txt"
   0 /tmp/ppmddumpfont-XXXXXX/stdout
48129 /tmp/ppmddumpfont-XXXXXX/font-report.txt
48129 total

The byte counts are from the installed standard font and can vary with the font or Netpbm build. The important result is that standard output is empty while the report on standard error is non-empty and the exit status is zero.

Read the beginning of the report:

$ sed -n '1,14p' "$workdir/font-report.txt"
ppmddumpfont: Font has 95 characters
ppmddumpfont: Font has code points 32 through 126
ppmddumpfont: Code point 32:
ppmddumpfont:   skip before: 0 pixels; skip after: 21 pixels; 0 commands:
ppmddumpfont: Code point 33:
ppmddumpfont:   skip before: 251 pixels; skip after: 5 pixels; 8 commands:
ppmddumpfont:     MOVEPEN 0 -12
ppmddumpfont:     DRAWLINE 0 2

The report describes the character range, spacing values and drawing commands for each code point. It is a diagnostic representation, not a new Ppmdfont file. Keep the original input if another Netpbm tool needs to consume it.

4. Inspect a real file without overwriting it

For an existing font, use an explicit report destination in a directory where you can write:

$ input=/path/to/custom.ppmdfont
$ report=/path/to/custom.ppmdfont.txt
$ test -r "$input" || { printf 'cannot read %s\n' "$input" >&2; exit 1; }
$ ppmddumpfont < "$input" 2> "$report"
$ status=$?
$ if [ "$status" -eq 0 ]; then
>     printf 'dump written to %s\n' "$report"
> else
>     printf 'ppmddumpfont failed with status %s\n' "$status" >&2
> fi

This uses ordinary user privileges. Use sudo only if the input or report directory is genuinely protected and your system policy permits that access. Elevated privileges are not a requirement of ppmddumpfont, and they do not repair invalid font data.

5. Diagnose the common failures

If you pass a filename as an argument, the installed command still reads standard input. With a valid file left unpiped, it reports an input-header error and returns status 1:

$ ppmddumpfont "$workdir/standard.ppmdfont" 2> "$workdir/error.txt"
$ printf '%s\n' "$?"
1
$ sed -n '1p' "$workdir/error.txt"
ppmddumpfont: Unable to read the header from the font file.  errno=0 (Success)

An empty pipe produces the same class of failure. Recheck the redirection, the path and the file size:

$ wc -c /path/to/custom.ppmdfont
$ test -s /path/to/custom.ppmdfont && echo non-empty
$ ppmddumpfont < /path/to/custom.ppmdfont 2> dump-errors.txt
$ printf 'status: %s\n' "$?"

Do not treat errno=0 (Success) in that diagnostic as a successful dump. The authoritative check is the process exit status, followed by whether a report was produced. A zero status means the command parsed the input; it does not prove that a font is suitable for every later drawing operation.