As title, I have one line shapefile with many segments:
How to use QGIS to quickly edit this line shapefile and output a new file looks like the original one, but with only one segment (its attribute table only has one row)?
Create a new field of integer type and give one value for all rows in this field. Then use dissolve tool from
Vector -> Geoprocessing tools -> Dissolve, if you are using QGIS 2.14.7, and select the NewField as a base to dissolve your polygons. If you are using QGIS 2.16.3, then go to
Processing toolbox -> QGIS geoalgorithms -> Vector geometry tools -> Dissolve.
Or you can use
Singlepart to multipatrs tool from
Vector -> geometry tools and do the same process of selecting the new field with one value for all rows.