Automate batch job processing


gmt batch mainscript -Nprefix -Tnjobs|min/max/inc[+n]|timefile[+pwidth][+sfirst][+w[str]] [ -Iincludefile ] [ -M[job] ] [ -Q[s] ] [ -Sbpreflight ] [ -Sfpostflight ] [ -V[level] ] [ -W[workdir] ] [ -Z ] [ -x[[-]n] ] [ --PAR=value ]

Note: No space is allowed between the option flag and the associated arguments.


The batch module can generate GMT processing jobs using a single master script that is repeated for all jobs, with some variation using specific job variables. The module simplifies (and hides) most of the steps normally needed to set up a full-blown processing sequence. Instead, the user can focus on composing the main processing script and let the parallel execution of jobs be automatic. We can set up required data sets and do one-time calculations via an optional preflight script. After completion we can optionally assemble the data output and make summary plots or similar in the postflight script.

Required Arguments


Name of a stand-alone GMT modern mode processing script that makes the parameter-dependent calculations. The script may access job variables, such as job number and others defined below, and may be written using the Bourne shell (.sh), the Bourne again shell (.bash), the csh (.csh) or DOS batch language (.bat). The script language is inferred from the file extension and we build hidden batch scripts using the same language. Parameters that can be accessed are discussed below.


Determines the prefix of the batch file products and the final sub-directory with all job products.


Either specify how many jobs to make, create a one-column data set width values from min to max every inc (append +n if inc is number of jobs instead), or supply a file with a set of parameters, one record (i.e., row) per job. The values in the columns will be available to the mainscript as named variables BATCH_COL0, BATCH_COL1, etc., while any trailing text can be accessed via the variable BATCH_TEXT. Append +w to split the trailing string into individual words that can be accessed via variables BATCH_WORD0, BATCH_WORD1, etc. By default we use any white-space to separate words. Append str to select another character(s) as the valid separator(s). The number of records equals the number of jobs. Note that the preflight script is allowed to create timefile, hence we check for its existence both before and after the preflight script has completed. Normally, the job numbering starts at 0; you can change this by appending a different starting job number via +sfirst. Note: All jobs are still included; this modifier only affects the numbering of the given jobs. Finally, +p can be used to set the tag width of the format used in naming jobs. For instance, name_000010.grd has a tag width of 6. By default, this is automatically set but if you are splitting large jobs across several computers (via +s) then you must use the same tag width for all names.

Optional Arguments


Insert the contents of includefile into the script that is accessed by all batch scripts. This mechanism is used to add information (typically constant variable assignments) that the mainscript and any optional -S scripts can rely on.


Instead of making and launching the full processing sequence, select a single master job [0] for testing. The master job will be run and its product(s) are placed in the top directory. While any preflight script will be run prior to the master job, the postflight script will not be executed (but it will be created).


Debugging: Leave all files and directories we create behind for inspection. Alternatively, append s to only build the batch scripts but not perform any executions. One exception involves the optional preflight script derived from -Sb which is always executed since it may produce data needed when building the main batch (or master) scripts.


The optional GMT modern mode preflight (written in the same scripting language as mainscript) can be used to download or copy data files or create files (such as timefile) that will be needed by mainscript. It is always run before the main sequence of batch scripts.


The optional postflight (written in the same scripting language as mainscript) can be used to perform final processing steps following the completion of all the individual jobs, such as assembling all the products into a single larger file. The script may also make one or more illustrations using the products or stacked data after the main processing is completed. It does not have to be a GMT script.

-V[level] (more …)

Select verbosity level [w].


By default, all temporary files and job products are created in the subdirectory prefix set via -N. You can override that selection by giving another workdir as a relative or full directory path. If no path is given then we create a working directory in the system temp folder named prefix. The main benefit of a working directory is to avoid endless syncing by agents like DropBox or TimeMachine, or to avoid problems related to low space in the main directory. The product files will still be placed in the prefix directory. The workdir is removed unless -Q is specified for debugging.


Erase the mainscript and all input scripts given via -I and -S upon completion. Not compatible with -Q.


Limit the number of cores to use when loading up the cores. By default we try to use all available cores. Append n to only use n cores (if too large it will be truncated to the maximum cores available). Finally, give a negative n to select (all - n) cores (or at least 1 if n equals or exceeds all). The parallel processing does not depend on OpenMP; new jobs are launched when the previous ones complete.

-^ or just -

Print a short message about the syntax of the command, then exit (NOTE: on Windows just use -).

-+ or just +

Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exit.

-? or no arguments

Print a complete usage (help) message, including the explanation of all options, then exit.


Temporarily override a GMT default setting; repeatable. See gmt.conf for parameters.


Several parameters are automatically assigned and can be used when composing the mainscript and the optional preflight and postflight scripts. There are two sets of parameters: Those that are constants and those that change with the job number. The constants are accessible by all the scripts: BATCH_PREFIX: The common prefix of the batch jobs (it is set with -N). BATCH_NJOBS: The total number of jobs (given or inferred from -T). Also, if -I was used then any static parameters listed therein will be available to all the scripts as well. In addition, the mainscript also has access to parameters that vary with the job counter: BATCH_JOB: The current job number (an integer, e.g., 136), BATCH_TAG: The formatted job number given the precision (a string, e.g., 000136), and BATCH_NAME: The name prefix unique to the current job (i.e., prefix_BATCH_TAG), Furthermore, if a timefile was given then variables BATCH_COL0, BATCH_COL1, etc. are also set, yielding one variable per column in timefile. If timefile has trailing text then that text can be accessed via the variable BATCH_TEXT, and if word-splitting was explicitly requested by +w modifier to -T then the trailing text is also split into individual word parameters BATCH_WORD0, BATCH_WORD1, etc. Note: Any product(s) made by the processing scripts should be named using BATCH_NAME as their name prefix as these will be automatically moved up to the starting directory upon completion.

Data Files

The batch scripts will be able to find any files present in the starting directory when batch was initiated, as well as any new files produced by mainscript or the optional scripts set via -S. No path specification is needed to access these files. Other files may require full paths unless their directories were already included in the DIR_DATA setting.

Constructing the Main Script

A batch sequence is not very interesting if nothing changes between calls. For the process to change you need to have your mainscript either access a different data set as the job number changes, or you need to access only a varying subset of a data set, or the processing parameters need to change, or all of the above. There are several strategies you can use to accomplish these effects:

  1. Your timefile passed to -T may list names of specific data files and you simply have your mainscript use the relevant BATCH_TEXT or BATCH_WORD? to access the job-specific file name.

  2. You have a 3-D grid (or a stack of 2-D grids) and you want to interpolate along the axis perpendicular to the 2-D slices (e.g., time, or it could be depth). In this situation you will use the module grdinterpolate to have the mainscript obtain a slice for the correct time (this may be an interpolation between two different times or depths) and process this temporary grid file.

  3. You may be creating data on the fly using gmtmath or grdmath, or perhaps processing data slightly differently per job (using parameters in the timefile) and computing these or the changes between jobs.

  4. Use your imagination to pass whatever arguments are needed via timefile.

Technical Details

The batch module creates several hidden script files that are used in the generation of the products (here we have left the script file extension off since it depends on the scripting language used): batch_init (initializes variables related to the overall batch job and includes the contents of the optional includefile), batch_preflight (optional since it derives from -Sb and computes or prepares needed data files), batch_postflight (optional since it derives from -Sf and processes files once all the batch job complete), batch_job (accepts a job counter argument and processes data for those parameters), and batch_cleanup (removes temporary files at the end of the process). For each job, there is a separate batch_params_###### script that provides job-specific variables (e.g., job number and anything given via -T). The preflight and postflight scripts have access to the information in batch_init, while the batch_job script in addition has access to the job-specific parameter file. Using the -Q option will just produce these scripts which you can then examine. Note: The mainscript is duplicated per job and many of these are run simultaneously on all available cores. Multi-treaded GMT modules will therefore be limited to a single core per call. Because we do not know how many products each batch job makes, we ensure each job creates a unique file when it is finished. Checking for these special (and empty) files is how batch learns that a particular job has completed and it is time to launch another one.

Hints for Batch Makers

Composing batch jobs is relatively simple, but you have to think in terms of variables. Examine the examples we describe. Then, start by making a single script (i.e., your mainscript) and identify which things should change with time (i.e., with the job number). Create variables for these values. If they are among the listed parameters that batch creates automatically then use those names. Unless you only require the job number you will need to make a file that you can pass via -T. This file should then have all the values you need, per job (i.e., per row), with values across all the columns you need. If you need to assign various fixed variables that do not change with time, then your mainscript will look shorter and cleaner if you offload those assignments to a separate includefile (via -I). To test your mainscript, start by using options -Q -M to ensure that your master job results are correct. The -M option simply runs one job of your batch sequence (you can select which one via the -M arguments [0]). Fix any issues with your use of variables and options until this works. You can then try to remove -Q. We recommend you make a very short (i.e., via -T) and small batch sequence so you don’t have to wait very long to see the result. Once things are working you can beef up number of jobs.


We extract a subset of bathymetry for the Gulf of Guinea from the 2x2 arc minute resolution Earth DEM and compute Gaussian filtered high-pass grids using filter widths ranging from 10 to 200 km in steps of 10 km. When the grids are all completed we determine the standard deviation in the result. To replicate our setup, try:

cat << EOF >
gmt begin
    gmt math -o0 -T10/200/10 T = widths.txt
    gmt grdcut -R-10/20/-10/20 @earth_relief_02m -Gdata.grd
gmt end
cat << EOF >
gmt begin
    gmt grdfilter data.grd -Fg\${BATCH_COL0}+h -G\${BATCH_NAME}.grd -D2
gmt end
cat << EOF >
gmt begin \${BATCH_PREFIX} pdf
    gmt grdmath \${BATCH_PREFIX}_*.grd -S STD = \${BATCH_PREFIX}_std.grd
    gmt grdimage \${BATCH_PREFIX}_std.grd -B -B+t"STD of Gaussians residuals" -Chot
    gmt coast -Wthin,white
gmt end show
gmt batch -Twidths.txt -Nfilter -V -Z

Of course, the syntax of how variables are used vary according to the scripting language. Here, we actually build the,, and scripts on the fly, hence we need to escape any variables (since they start with a dollar sign that we need to be written verbatim). At the end of the execution we find 20 grids (e.g., such as filter_07.grd), as well as the filter_std.grd file obtained by stacking all the individual scripts and computing a standard deviation. The information needed to do all of this is hidden from the user; the actual batch scripts that we execute are derived from the user-provided script and batch* supplies the extra machinery. The batch module automatically manages the parallel execution loop over all jobs using all available cores and launches new jobs as old ones complete.

As another example, we get a list of all European countries and make a simple coast plot of each of them, placing their name in the title and the 2-character ISO code in the upper left corner, then in postflight we combine all the individual PDFs into a single file and delete them:

cat << EOF >
gmt begin
    gmt coast -E=EU+l > countries.txt
gmt end
cat << EOF >
gmt begin \${BATCH_NAME} pdf
    gmt coast -R\${BATCH_WORD0}+r2 -JQ10c -Glightgray -Slightblue -B -B+t"\${BATCH_WORD1}" -E\${BATCH_WORD0}+gred+p0.5p
    echo \${BATCH_WORD0} | gmt text -F+f16p+jTL+cTL -Gwhite -W1p
gmt end
cat << EOF >
rm -f \${BATCH_PREFIX}_*.pdf
gmt batch -Tcountries.txt+w"\t" -Ncountries -V -W -Zs

Here, the postflight script is not even a GMT script; it simply runs gs and deletes what we don’t want.