Piping & Redirection

The pipe | feeds one command's output straight into another's input, this is what makes the command line so powerful, chaining small, focused tools into a bigger one.

Example: filtering and logging

$ ls -la | grep ".txt"
$ echo "Deploy finished" >> deploy.log

The first command lists only files whose names contain ".txt", the same grep filtering idea from the previous lesson, applied to a directory listing instead of a process list. > redirects output into a file, overwriting whatever was there before; >> (used above) appends instead, adding a new line to deploy.log without erasing anything already logged, exactly the distinction you want when writing to a log file that's supposed to accumulate history rather than get wiped on every write.