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2-Cent Tips

2-cent Tip: Conditional pipes

Ben Okopnik [ben at linuxgazette.net]

Mon, 3 Aug 2009 22:43:05 -0500

In using Debian/Ubuntu, I often find myself doing an "apt-cache search <foo>" - i.e., searching the package database. Unfortunately, the copious return from the search often overruns my screen, requiring paging up - or, if I do remember to pipe the output to 'less', turns out to be annoyingly short (and now requires quitting out of the pager.) So, a little while ago, I decided to be lazy^Wefficient and write a script... actually, a function - a script wouldn't do, since the variable I'm looking for only exists in the current shell environment.

From my ~/.bashrc:

ac () 
    out=$(/usr/bin/apt-cache search "$@")
    if [ $(($(echo "$out"|/usr/bin/wc -l)+2)) -ge $LINES ]
        echo "$out" | /usr/bin/less
        echo "$out"
export -f ac

Using the $LINES Bash variable, which tells us how many lines our current terminal is capable of displaying, makes it relatively simple to decide whether to use a pipe or not. I also adjust the comparison a bit to account for the prompt.

* Ben Okopnik * Editor-in-Chief, Linux Gazette * http://LinuxGazette.NET *

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Published in Issue 166 of Linux Gazette, September 2009