Runs a PNG through PngOut multiple times at different block sizes. More details @ http://nicj.net/2012/05/15/pngoutbatch

PngOutBatch.cmd

@echo off
setlocal enabledelayedexpansion

REM
REM PngOutBatch
REM
REM Nic Jansma - nic@nicj.net
REM
REM Runs a PNG through PngOut multiple times at different block sizes.  Shows the
REM file-size savings during and at the end.
REM
REM More details: http://nicj.net/2012/05/15/pngoutbatch
REM
REM Usage: PngOutBatch.cmd [image.png] [number of passes per block size - default 5]
REM

if {%1}=={} (
    call :Usage
    exit /b 1
)

REM @morewry added pngoutDir so it's aware of the location of pngout
set pngoutDir=%~d0%~p0
set filePath=%1

set numberOfPasses=5
if NOT {%2}=={} (
    set numberOfPasses=%2
)

REM
REM Save original file size
REM
call :FileSize !filePath!
set origFileSize=!fileSize!
set currentFileSize=!origFileSize!

REM
REM Run PngOut in a loop
REM
for %%b in (0 128 192 256 512 1024 2048 4096 8192) do (
    set blockSize=%%b

    echo Blocksize: !blockSize!
    for /l %%n in (1,1,!numberOfPasses!) do (
        set passNumber=%%n
        REM @morewry added pngoutDir so it's aware of the location of pngout
        call !pngoutDir!pngout /b!blockSize! /r !filePath! > nul

        REM check file size after this iteration
        call :FileSize !filePath!
        set thisFileSize=!fileSize!
        set /a savings = currentFileSize - thisFileSize

        if !savings! GTR 0 (
            echo Iteration #!passNumber!: Saved !savings! bytes
        ) else (
            echo Iteration #!passNumber!: No savings
        )

        set currentFileSize=!thisFileSize!
    )
)

REM
REM Check final file size
REM
call :FileSize !filePath!
set finalFileSize=!fileSize!
set /a savings = origFileSize - finalFileSize

if !savings! GTR 0 (
    echo !filePath!: SUCCESS: !origFileSize! bytes originally, !finalFileSize! bytes final: !savings! bytes saved
) else (
    echo !filePath!: No change
)

endlocal
exit /b 0

REM
REM Helper functions
REM
:FileSize
    set fileSize=%~z1
    goto :eof

:Usage
    echo PngOutBatch.cmd [filename] [number of passes, defaults to 5]
    goto :eof

I find this is really slow for all 24-bit PNGs in comparison to http://www.ardfry.com/pngoutwin/

Do you know if there's a bash-script equivalent (or something else Linux-friendly) of this?

Not that I found at the time (tho I needed a Win version)