Automatically print number of lines of command line output

Question

In my fish shell, I am using fish command timer to automatically show the duration of each command after it has been executed. This is a neat feature, which I recommend.

Now I want something similar in addition to that: The number of lines, i.e. after each command line I execute, the number of lines printed to stdout and/or stderr should be printed to stdout, too.

Example:

Instead of

> cat /etc/mpd.conf
pid_file "/run/mpd/mpd.pid"
db_file "/var/lib/mpd/mpd.db"
state_file "/var/lib/mpd/mpdstate"
playlist_directory "/var/lib/mpd/playlists"

I want to see

> cat /etc/mpd.conf
pid_file "/run/mpd/mpd.pid"
db_file "/var/lib/mpd/mpd.db"
state_file "/var/lib/mpd/mpdstate"
playlist_directory "/var/lib/mpd/playlists"

[ 4 lines ]

Some notes:

• There are some manual solutions to print the number of output lines of a command here, but I want this to be a permanent feature implemented in my fish config.
• I don't want to execute the command twice (for obvious reasons like the lack of idempotency etc.)
• A solution for bash (instead of fish) may point in the right direction.

The command timer works with a postexec event that is fired after executing a command line, but that does not exactly solve my problem, so I am in need of an approach.

Answer 1

Try replacing cat /etc/mpd.conf with cat /etc/mpd.conf | tee /proc/self/fd/2 | echo -e "\n[ $(wc -l) lines ]"

If you can't use /proc/self/fd/ try splitting it into 2 commands or use the && operator for something like cat /etc/mpd.conf && echo "Number of lines: $(cat /etc/mpd.conf | wc -l)"

from wc man page:

-l, --lines print the newline counts