Advance a PBM Life Pattern One Generation with pbmlife

You will use Netpbm's pbmlife to read a PBM image, apply one generation of Conway's Game of Life, and write the next PBM image without changing the input. Allow about ten minutes. You need Netpbm 2:11.05.02-1.1build1 or a compatible installation, a shell, and a PBM file that you are willing to test. The examples use an ordinary user account and do not need sudo.

Checkpoint: this guide advances one generation only. Repeating the command advances the result again, so keep the generations in separate files while you are checking a pattern.

1. Confirm the installed command

Check which executable will run and record the package version. These are read-only checks:

$ command -v pbmlife
/usr/bin/pbmlife
$ dpkg-query -W -f='${Package} ${Version}\n' netpbm
netpbm 2:11.05.02-1.1build1

The installed manual describes pbmlife [pbmfile]. The optional file argument selects the input; omitting it makes the program read standard input. There are no options specific to pbmlife, although Netpbm common options are recognised. Do not assume that a flag from another image utility applies here.

2. Keep a source image and choose a new destination

Make a working copy if the source is valuable, then choose a destination that does not already contain a result:

$ cp --preserve=all pattern.pbm pattern.pbm.before-life
$ pbmlife pattern.pbm > pattern.pbm.next

The first command changes state by creating a backup, but it leaves the original content untouched. The second command writes the transformed image to a new file. Shell redirection truncates an existing destination before pbmlife can report an error, so do not point > at the only copy of a useful image.

Checkpoint: if the command exits non-zero, inspect the error and keep pattern.pbm. If the new file is incomplete, remove only that disposable output after checking its path, then rerun to another new name. The backup can be restored with cp --preserve=all pattern.pbm.before-life pattern.pbm if you deliberately need to undo a replacement.

3. Test a small blinker

A three-cell line is a useful smoke test. In the PBM format, 1 is black and 0 is white. The pbmlife manual gives the Life interpretation in the opposite visual terms: a white pixel is a live beastie and a black pixel is empty space. Therefore this test puts live cells in the zero-valued pixels:

$ printf '%s\n' \
  'P1' \
  '5 5' \
  '1 1 1 1 1' \
  '1 1 1 1 1' \
  '1 0 0 0 1' \
  '1 1 1 1 1' \
  '1 1 1 1 1' | pbmlife | pbmtoascii -1
MM"MM
MM MM
"""""

pbmtoascii -1 is only a terminal preview; it is not part of the pbmlife operation. The output above is wrapped vertically because the preview maps two image rows to each character. The meaningful checks are that the pipeline exits successfully and that the middle run changes orientation after one generation. If pbmtoascii is not installed, save the output as a PBM and inspect it with an image viewer or another PBM-aware Netpbm utility.

4. Read from standard input when composing a pipeline

For a file, pass its path as the only positional argument. For generated or previously filtered PBM data, omit the argument and pipe the data in:

$ pbmlife pattern.pbm > pattern.pbm.next
$ some-pbm-producing-command | pbmlife > generated-next.pbm
$ file generated-next.pbm
generated-next.pbm: Netpbm image data, size 5 x 5, rawbits

The exact file description depends on the dimensions and PBM encoding. The important part is that the result remains a PBM image. A successful exit status means the program completed its conversion; it does not prove that the pattern is the one you intended. Check the dimensions and preview the result before using it in a later pipeline.

5. Handle failures without guessing

A missing input path is a normal file error, not a reason to add elevated privileges:

$ pbmlife /path/to/missing.pbm > next.pbm
pbmlife: Unable to open file '/path/to/missing.pbm' for reading.  fopen() returns errno 2 (No such file or directory)
$ printf 'exit status: %s\n' "$?"
exit status: 1

If this happens, check the path and readability without changing permissions:

$ ls -l /path/to/pattern.pbm
$ test -r /path/to/pattern.pbm && echo readable

Also check that the input really is PBM and that its dimensions match what the producer claims. Do not use sudo to hide an incorrect path or to overwrite a protected destination. If the destination directory genuinely belongs to a service or another user, stop and follow that system's change process instead of making a broad permission change.

6. Repeat generations safely

To advance several generations, chain distinct names so each step can be compared or discarded:

$ pbmlife pattern.pbm > pattern.g01.pbm
$ pbmlife pattern.g01.pbm > pattern.g02.pbm
$ pbmlife pattern.g02.pbm > pattern.g03.pbm

Each invocation applies exactly one generation. This is easier to audit than repeatedly overwriting one file, and it gives you a recovery point if a later command fails. Once you have verified the final image and no longer need an intermediate, remove only the named disposable files. Do not delete the original as part of an unattended one-liner.