linux - cut not cutting the columns when used with pipe

Question

I'm trying to grep and cut using pipes.
file:

c1 c2
e1 e2
e3 e4

this file has space-separated values, but when I execute

cut -f2 -d' ' | grep "e2" example.csv
output is e1 e2

the output should be e2 but I'm not sure if the cut takes input in some other format, in the man pages it says that file name if unspecified then input would be taken.

question from:https://stackoverflow.com/questions/65887783/cut-not-cutting-the-columns-when-used-with-pipe

Answer 1

You have it backwards. The output of cut must be sent to grep.

cut -f2 -d' ' example.csv | grep e2

Otherwise, grep operates on the file, not on its input, and cut operates on the standard input, which is coming from the outer context, probably your keyboard?

The pipeline takes the output of the left hand side command and connects it to the input of the right hand side one, not the other way round. The left hand side command doesn't know what the arguments of the right hand side command are (and vice versa).