Hi Datakanja, I am not entirely sure what you are trying to do, but the arguments
this should not happen are already separated per default POSIX parsing. You do not need --colsep. Thus parallel --dry-run -n 2 echo {} ::: this should not happen correctly produces on my macbook, with 2 processors: echo this should echo not happen as the maximum number of arguments assigned to echo will be 2, so the first two arguments are sent to processor 1 and the next two are sent to processor 2. If you want each processor to echo one argument at a time, then do: parallel --dry-run -n 1 echo {} ::: this should not happen which then gives: echo this echo should echo not echo happen This is what you want to do right? I hope this will be helpful. Best regards, Lianheng ================================================ Lianheng Tong Tel: +44 79 1758 3822 Room S4.02, Strand Building Fax: +44 20 7848 2420 Department of Physics lianheng.t...@kcl.ac.uk Kings College London Strand, London WC2R 2LS, U.K. ================================================ On 6 Jan 2014, at 11:06, ChessDoter wrote: > Hi Lianheng, > > thanks for avoiding calling me PEBE. ;-) > > Ok, i do see now, that the ` has to be escaped, like > > echo this should not happen | xargs -n 1 echo | parallel --dry-run -n 2 echo > \`echo {}\` > > Would you please provide a pointer to the solution of the --colsep problem? i > wasnt able to get rid of the xargs step for that on my own. > > Best regards > Datakanja > > Am 06.01.2014 11:42, schrieb Lianheng Tong: >> Hi, >> >> I think the problem you have encountered is a problem associated with a >> possible misunderstanding how POSIX command lines are interpreted by the >> system, rather than a particular problem with parallel. >> >> Best regards, >> >> Lianheng >> >> ================================================ >> Lianheng Tong Tel: +44 79 1758 3822 >> Room S4.02, Strand Building Fax: +44 20 7848 2420 >> Department of Physics lianheng.t...@kcl.ac.uk >> <mailto:lianheng.t...@kcl.ac.uk> >> Kings College London >> Strand, London WC2R 2LS, U.K. >> ================================================ >> >> On 6 Jan 2014, at 10:35, ChessDoter wrote: >> >>> hello, >>> >>> far from being a power user with linux... >>> >>> ... i happen to play with parallel... >>> >>> and get confused/surprised at times. Like so: >>> >>> echo this should not happen | xargs -n 1 echo | parallel --dry-run -n 2 >>> echo `echo {}` >>> >>> First, i was not able to separate the 4 words into different arguments with >>> --colsep ' ', so that is why i used xargs in the mix. >>> Then, i did not expect --dry-run to allow for execution of the embedded >>> `echo` command. >>> >>> Ok, i can imagine scenarios, when this comes in handily... >>> >>> My current conclusion is: be VERY careful with this powerful tool, test >>> thoroughly before execution but even then... (can i trust it?) beware of >>> unexpected side-effects. >>> >>> just my 2 cents