Command Line Introduction

Interactive Shell

Starting GRASS...
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The GRASS command line interface allows you to start a GRASS session to run GRASS commands, execute scripts, or open the GUI.

Here we create a new project for the NAD83(HARN)/North Carolina coordinate reference system (EPSG:3358) and start a GRASS session:

grass -c EPSG:3358 {project directory} --text

We can now execute GRASS tools as commands in a new shell. For example, we can import an elevation raster and calculate its univariate statistics.

r.import input=elevation.tif output=elevation resample=bilinear

Let's make sure the region is set to the elevation raster.

g.region raster=elevation -p

projection: 99 (Lambert Conformal Conic)
zone:       0
datum:      nad83
ellipsoid:  a=6378137 es=0.006694380022900787
north:      228500
south:      215000
west:       630000
east:       645000
nsres:      10
ewres:      10
rows:       1350
cols:       1500
cells:      2025000

Now we can calculate the univariate statistics of the elevation raster.

r.univar elevation

total null and non-null cells: 2025000
total null cells: 0

Of the non-null cells:
----------------------
n: 2025000
minimum: 55.5788
maximum: 156.33
range: 100.751
mean: 110.375
mean of absolute values: 110.375
standard deviation: 20.3153
variance: 412.712
variation coefficient: 18.4057 %
sum: 223510266.558102

Command Execution

GRASS commands can be executed directly in the terminal. Here we execute the r.slope.aspect tool on an elevation raster from our project.

grass {project directory} --exec \
    r.slope.aspect elevation=elevation slope=slope aspect=aspect

Scripting

The grass command can also execute scripts. Here we create a Bash script, export_slope.sh, to export the slope map as a PNG.

#!/bin/bash
g.region raster=elevation
r.slope.aspect elevation=elevation slope=slope aspect=aspect
r.colors map=slope color=sepia
r.out.png input=slope output=slope -w

grass {project directory} --exec bash export_slope.sh

Python scripts can also be executed by the grass command when a Python interpreter is provided. Here we create a Python script, export_aspect.py, to export the aspect map as a PNG.

import grass.script as gs

gs.run_command('g.region', raster='elevation')
gs.run_command('r.slope.aspect', elevation='elevation', slope='slope', aspect='aspect')
gs.run_command('r.colors', map='aspect', color='aspect')
gs.run_command('r.out.png', input='aspect', output='aspect', overwrite=True)

Now execute the Python script.

grass {project directory} --exec python export_aspect.py

Scripts can also run from the interactive shell providing adding to the flexibility of the command line interface.