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Software Exercise 4.3: Passing Arguments Through the Wrapper Script

Objective: Add arguments to a wrapper script to make it more flexible and modular

Why learn this?: Using script arguments will allow you to use the same script for multiple jobs, by providing different inputs or parameters. These arguments are normally passed on the command line, but in our world of job submission, the arguments will be listed in the submit file, in the arguments line.

Identifying Potential Arguments

  1. In the same directory as the last exercise, make sure you're in the directory with your BLAST job submission.

  2. What values might we want to input to the script via arguments? Hint: anything that we might want to change if we were to run the script many times.

In this example, some values we might want to change are the name of the comparison database, the input file, and the output file.

Modifying Files

  1. We are going to add three arguments to the wrapper script, controlling the database, input and output file.

  2. Make a copy of your last submit file and open it for editing. Add an arguments line, or uncomment the one that exists, and add the three input values mentioned above.

  3. The arguments line in your submit file should look like this: 

    arguments = pdbaa mouse.fa results3.txt

    (We're using results3.txt) to distinguish between the previous two runs.)

  4. For bash (the language of our current wrapper script), the variables $1, $2 and $3 represent the first, second, and third arguments, respectively. Thus, in the main command of the script, replace the various names with these variables: 

    ncbi-blast-2.12.0+/bin/blastx -db $1/$1 -query $2 -out $3

    If your wrapper script is in a different language, you should use that language's syntax for reading in variables from the command line.

  5. Once these changes are made, submit your jobs with condor_submit. Use condor_q -nobatch to see what the job command looks like to HTCondor.

It is now easy to change the inputs for the job; we can write them into the arguments line of the submit file and they will be propagated to the command in the wrapper script. We can even turn the submit file arguments into their own variables when submitting multiple jobs at once.

Readability with Variables

One of the downsides of this approach, is that our command has become harder to read. The original script contains all the information at a glance:

ncbi-blast-2.12.0+/bin/blastx -db pdbaa/pdbaa -query mouse.fa -out results2.txt

But our new version is more cryptic -- what is $1?: 

ncbi-blast-2.10.1+/bin/blastx -db $1 -query $2 -out $3

One way to overcome this is to create our own variable names inside the wrapper script and assign the argument values to them. Here is an example for our BLAST script: 

#!/bin/bash

DATABASE=$1
INFILE=$2
OUTFILE=$3

tar -xzf ncbi-blast-2.10.1+-x64-linux.tar.gz 
tar -xzf pdbaa.tar.gz

ncbi-blast-2.10.1+/bin/blastx -db $DATABASE/$DATABASE -query $INFILE -out $OUTFILE

Here, we are assigning the input arguments ($1, $2 and $3) to new variable names, and then using those names ($DATABASE, $INFILE, and $OUTFILE) in the command, which is easier to read.

  1. Edit your script to match the above syntax.

  2. Submit your jobs with condor_submit. When the job finishes, look at the job's standard output file to see how the variables printed.