GNU 可以在程序退出之前并行输出 stdout 吗？

Question 1

我想你正在寻找--ungroup。手册页说：

--group  Group output. Output from each jobs is grouped 
         together and is only printed when the command is finished. 

         --group is the default. Can be reversed with -u.

-u当然是的同义词--ungroup。

Answer

我想你正在寻找--ungroup。手册页说：

--group  Group output. Output from each jobs is grouped 
         together and is only printed when the command is finished. 

         --group is the default. Can be reversed with -u.

-u当然是的同义词--ungroup。

Question 2

要查看一些并行作业的进度，请尝试--tmuxpane --fg：

parallel --tmuxpane --fg seq {} 10000000 ::: {1..100}

您也可能正在寻找-u或（更有可能）--lb。从man parallel：

   --line-buffer
   --lb
       Buffer output on line basis. --group will keep the output together
       for a whole job. --ungroup allows output to mixup with half a line
       coming from one job and half a line coming from another job.
       --line-buffer fits between these two: GNU parallel will print a full
       line, but will allow for mixing lines of different jobs.

       --line-buffer takes more CPU power than both --group and --ungroup,
       but can be much faster than --group if the CPU is not the limiting
       factor.

       Normally --line-buffer does not buffer on disk, and can thus process
       an infinite amount of data, but it will buffer on disk when combined
       with: --keep-order, --results, --compress, and --files. This will
       make it as slow as --group and will limit output to the available
       disk space.

       With --keep-order --line-buffer will output lines from the first job
       while it is running, then lines from the second job while that is
       running. It will buffer full lines, but jobs will not mix. Compare:

         parallel -j0 'echo {};sleep {};echo {}' ::: 1 3 2 4
         parallel -j0 --lb 'echo {};sleep {};echo {}' ::: 1 3 2 4
         parallel -j0 -k --lb 'echo {};sleep {};echo {}' ::: 1 3 2 4

       See also: --group --ungroup

[...]

   --ungroup
   -u  Ungroup output.  Output is printed as soon as possible and by passes
       GNU parallel internal processing. This may cause output from
       different commands to be mixed thus should only be used if you do not
       care about the output. Compare these:

         seq 4 | parallel -j0 \
           'sleep {};echo -n start{};sleep {};echo {}end'
         seq 4 | parallel -u -j0 \
           'sleep {};echo -n start{};sleep {};echo {}end'

       It also disables --tag. GNU parallel outputs faster with -u. Compare
       the speeds of these:

         parallel seq ::: 300000000 >/dev/null
         parallel -u seq ::: 300000000 >/dev/null
         parallel --line-buffer seq ::: 300000000 >/dev/null

       Can be reversed with --group.

       See also: --line-buffer --group

一个闪亮的例子-u是 stdout 和 stderr 混合在同一行中：

echo -n 'This is stdout (';echo -n stderr >&2 ; echo ')'

--lb 使用和时，这将被错误地格式化--group。

-u但由于进程之间的半行混合，甚至不能保证它会被正确格式化：http://mywiki.wooledge.org/BashPitfalls#Non-atomic_writes_with_xargs_-P

您也可以尝试： --latest-line ，它在屏幕上为每个作业保留一行并在此处打印最新行。

Answer