PROJ is a generic coordinate transformation software that transforms geospatial coordinates from one coordinate reference system (CRS) to another. It is currently used in many GIS softwares, but can also be used through an API or by command-line tools.
Below some usefull command lines:
Simple conversion from a known coordinate system (CS) to another known CS :
here from UTM33N-WGS84 to WGS84
echo 357000 4676000 | cs2cs +init=epsg:32633 +to +init=epsg:4326
Should return
13d16'2.189"E 42d13'23.141"N 0.000
More documentation https://proj.org/usage/quickstart.html
to add some formatting to output, specify the format with “-f” as a printf format string. For example “-f %.8f” will return the coordinate in decimal degrees with 8 decimals
13.26727481 42.22309481 0.00000000
to input several coordinates at a time, either use a file and pipe with cat
cat coords_utm.txt | cs2cs +init=epsg:32633 +to +init=epsg:4326 -f %.8f
Should return the list of converted coordinates
13.26727481 42.22309481 0.00000000
13.54977927 42.05589846 0.00000000
and to output into a file, redirect with > symbol
cat coords_utm.txt | cs2cs +init=epsg:32633 +to +init=epsg:4326 -f %.8f > coords_dd_wgs84.txt
to input manually several coordinates, use EOF or whatever specific characters you like :
cs2cs EPSG:4326 EPSG:32631 <<EOF
45N 2E
EOF