NAME

       xjobs - construct command line and execute jobs in parallel

SYNOPSIS

       xjobs [options] [utility [argument ...]]

DESCRIPTION

       xjobs reads job descriptions line by line and executes them in parallel. It limits the number of parallel
       executing jobs and starts new jobs when jobs finish.  Therefore, it combines  the  arguments  from  every
       input  line  with  the  utility  and  arguments  given  on the command line. If no utility is given as an
       argument to xjobs, then the first argument on every job line will be used as utility. To execute  utility
       xjobs  searches  the  directories given in the PATH environment variable and uses the first file found in
       these directories.

       xjobs is most useful on multiprocessor machines when one needs to execute several time consuming commands
       that  could  possibly  be  run in parallel. With xjobs this can be achieved easily, and it is possible to
       limit the load of the machine to a useful value.  It works similar to xargs, but starts several processes
       simultaneously and gives only one line of arguments to each utility call.

       By using I/O redirectors the standard input, output, and error stream of executed jobs can be redirected.
       Use < to redirect standard input, > to redirect standard output,  >!  to  redirect  standard  output  and
       overwrite  an  existing  file,  >>  to  append  standard  output to an existing file, >& to redirect both
       standard output and standard error output to the same file, and >>& to append both  standard  output  and
       standard error output to the same file.

       If  passed  on  the  command  line,  these  operators  specify  the  default  I/O redirection that can be
       overwritten by specifying another redirector to a specific job on its argument  line.   After  all  these
       operators  a  filename  is  expected. See EXAMPLES below for an example.  If you need more advanced shell
       features than the redirection operators supported  by  xjobs,  then  use  as  utility  a  shell  of  your
       preference.

       Every  job line can be preceeded by a "cd directory;" command that tells xjobs in which directory the job
       shall be executed. For every line this can only be used once. For more complex scripting, please pass the
       line to execute to a shell of your choice.

       xjobs constructs the arguments of the jobs to execute from each input line. Each input line will create a
       seperate job, whereas newline character are handled as regular whitespace by xargs. To be able to include
       whitespace  charakters  in  arguments,  either preceed them with a backslash or quote them with single or
       doublequote charakters. A backslash charakter preceeding a newline will make  xjobs  ignore  the  newline
       character,  thus  giving  you  the  ability  to pass arguments for a single job across multiple lines. To
       include quotation marks in quoted arguments, preceed them  with  a  backslash.   Lines  passed  to  xjobs
       beginning with a # charakter are interpreted as comments.

       Finally,  xjobs  also  includes  a  mechanism for serializing the execution.  Like this it is possible to
       parallelize independent jobs and sequence jobs that have a dependency. This can be achieved by  inserting
       a  line  that only consists of two percentage charakters in sequence (%%).  All jobs before this sequence
       point are executed at the requested number of jobs in parallel. When hitting  the  sequence  point  xjobs
       waits for all processes to finish and then continues starting jobs that follow the sequence point.

       When  passing  a  named  pipe  (i.e. a file name created by mkfifo) via option -s as an input, xjobs will
       close and reopen the fifo when reaching end-of-file. Like this it is possible to setup  an  xjobs  server
       and sending jobs to this server from muliple programs. See section EXAMPLES below for an example.

OPTIONS

       -j <jobs>
              Sets  the  maximum  number of jobs that are started in parallel. The default value is to limit the
              number executing jobs is equal to the number of online processors in the  system.  If  the  number
              passed  as  <jobs>  is  followed by an 'x' charakter (e.g. 2.5x), the value is multiplied with the
              number of online processors before setting the job limit. I.e.  having a  machine  with  4  online
              processors and passing 2.5x as an argument to option -j will yield a joblimit of 10 jobs.

       -s <script>
              Use file script instead of the standard input to read the job descriptions.

       -n     Redirect standard output and standard error output of executed jobs to /dev/null.

       -l <num>
              Combine the arguments of <num> input lines for a single job.

       -p     Start jobs interactively, prompting the user.

       -q <num>
              Limits the number of queued jobs to num elements. Normally xjobs reads in jobs from standard input
              or the give script and queues them if they cannot be started at once. With this option, xjobs will
              stop  reading  as soon as num jobs are queued and restart reading when a new job has been started.
              Like this xjobs allocates less memory. Use this option, if you pass huge number of jobs to  xjobs,
              to  limit memory consumption. It can also increase performance of xjobs, but be sure that jobs get
              fed fast enough to xjobs.

       -1     Pass one argument per job, which is expected to be terminated by a new-line character. No argument
              parsing  is  performed.  That  way  it  is  more  easy to process jobs where arguments may include
              whitespace character or other tokens that influence argument parsing.

       -0     Same as -1, but as a job and argument termination character  a  null-character  (\0)  is  expected
              instead  of a new-line character. That way also arguments with new-line character can be processed
              without escape sequences.

       -V     Print the version number of xjobs and exit.

       -v <level>
              Set verbosity of xjobs to level. Valid leves are: 0=silent, 1=error, 2=warning,  3=info,  4=debug.
              The default level of verbosity is 3.

EXAMPLES

       If you have a lot of .zip files that you want to extract, then use xjobs like this:

       $ ls -1 *.zip | xjobs unzip

       If you want to do the same without getting the output of each unzip task on your terminal, then try this:

       $ ls -1 *.zip | xjobs -n unzip

       To gzip all *.bak files in a given directory hierarchy, use it the following way:

       $ find . -name '*.bak' | xjobs gzip

       To  generate  index  files for a set of *.jar files, you can use the redirection feature of xjobs, and do
       the following:

       $ ls -1 *.jar | sed 's/\(.*\)/\1 > \1.idx/' | xjobs jar tf

       If you also want to capture the error output, than use >& instead of >.

       You can also use it to execute several different commands. Therefore, write a script file  that  contains
       every job you want to execute and pass it to xjobs with the option -s:

       $ cat - > script
       unzip my.zip
       tar xf my.tar
       lame --silent my.wav my.mp3
       crypt notsecret < mydata > secretfile
       ^D
       $ xjobs -s script

       To  be able to queue up jobs from multiple sources with xjobs, use a named pipe and pass it explicitly as
       input script. Then write the jobs to the named pipe:
       $ mkfifo /var/run/my_named_pipe
       $ xjobs -s /var/run/my_named_pipe &
       $ echo unzip 1.zip >> /var/run/my_named_pipe
       $ echo tar cf /backup/myhome.tar /home/me >> /var/run/my_named_pipe

ENVIRONMENT VARIABLES

       PATH Determines the location of command.

AUTHORS

       Thomas Maier-Komor <thomas@maier-komor.de>
       Donations via PayPal are welcome!

HOMEPAGE

       http://www.maier-komor.de/xjobs.html

LICENSE

       GNU General Public License Version 2

SEE ALSO

       xargs(1)