防止Ghostscript将错误写入标准输出

问题描述：

我正在使用Ghostscript将PDF文件的首页光栅化为JPEG.为避免创建临时文件，将PDF数据通过管道传递到Ghoscripts的stdin中，而将JPEG在stdout中排空".在GS接收到无效的PDF数据之前，该管道就像一个咒语一样起作用:它并没有像我期望的那样在stderr上报告所有错误消息，而是将一些消息写到了 stdout .

I'm using Ghostscript to rasterize the first page of a PDF file to JPEG. To avoid creating tempfiles, the PDF data is piped into Ghoscripts's stdin and the JPEG is "drained" on stdout. This pipeline works like a charm until GS receives invalid PDF data: Instead of reporting all error messages on stderr as I would have expected, it still writes some of the messages to stdout instead.

要复制:

$ echo "Not a PDF" >test.txt
$ /usr/bin/gs -q -sDEVICE=jpeg -dBATCH -dNOPAUSE -dFirstPage=1 -dLastPage=1 \
    -r300 -sOutputFile=- - < test.txt 2>/dev/null
Error: /undefined in Not
Operand stack:

Execution stack:
...

请注意，上面的2>/dev/null不会抑制错误消息. Ghostscript的文档已经警告说，向stdout进行写入需要-q标志来禁止显示stdout上的消息，但是我似乎仍然在这里遗漏了一些东西.

Note the 2>/dev/null above does not suppress the error messages. Ghostscript's documentation already warned that writing to stdout requires the -q flag to suppress messages on stdout, but I still seem to be missing something here.

答

如果您想真的使Ghostscript静音，请按如下所示修改您的命令行:

If you want to really silence Ghostscript, modify your command line like this:

/usr/bin/gs -q        \
     -sstdout=%stderr \
     -sDEVICE=jpeg    \
     -dBATCH          \
     -dNOPAUSE        \
     -dLastPage=1     \
     -r300            \
     -sOutputFile=-   \
     - < test.txt 2>/dev/null

添加的-sstdout=%stderr允许重定向Postscript stdout，同时仍允许驱动程序写入stdout. (该补丁自9月22日〜2001年以来一直存在于Ghostscript中.)

The addition of -sstdout=%stderr allows Postscript stdout to be redirected, while still allowing drivers to write to stdout. (That patch is in Ghostscript since ~2001, Sept 22.)

防止Ghostscript将错误写入标准输出

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