Imagine you have a CLI command cat myfile | ./my-filter
, and now you want to see all the lines not selected, essentially negating my-filter
. Here is a way to achieve that.
The "grep for complements" command is a useful tool for filtering out lines from a file that have not been selected by a custom filter. This can be achieved using a combination of cat
, your custom filter (./my-filter
), and grep
.
To use "grep for complements", follow these steps:
-
Ensure you have a file (
myfile
) containing the data you want to filter. -
Create or implement a custom filter program named
my-filter
that selects a subset of lines frommyfile
. -
Run the following command in your terminal:
cat myfile | ./my-filter | grep -F -v -f - myfile
Replace
myfile
with the path to your file.
cat myfile
: Reads the contents of the filemyfile
and outputs them../my-filter
: Runs your custom filter program, which selects a subset of lines from the input.grep -F -v -f - myfile
:grep
with the-F
option treats patterns as fixed strings,-v
selects non-matching lines, and-f -
tellsgrep
to use patterns from standard input (piped from the output of./my-filter
). Finally,myfile
specifies the file to search for the complement of the selected lines.
This command effectively filters out lines selected by ./my-filter
and displays the complement in myfile
.