remove all lines from a text file starting at first empty line

Question

What is the best way to remove all lines from a text file starting at first empty line in Bash? External tools (awk, sed...) can be used!

Example

1:          


        

Answer 1

Bet there are some more clever ways to do this, but here's one using bash's 'read' builtin. The question asks us to keep lines before the blank in one file and send lines after the blank to another file. You could send some of standard out one place and some another if you are willing to use 'exec' and reroute stdout mid-script, but I'm going to take a simpler approach and use a command line argument to let me know where the post-blank data should go:

#!/bin/bash

# script takes as argument the name of the file to send data once a blank line
# found
found_blank=0
while read stuff; do
    if [ -z $stuff ] ; then
            found_blank=1
    fi
    if [ $found_blank ] ; then
            echo $stuff > $1
    else
            echo $stuff
    fi
done

run it like this:

$ ./delete_from_empty.sh rest_of_stuff < demo

output is:

ABC
DEF

and 'rest_of_stuff' has

GHI

if you want the before-blank lines to go somewhere else besides stdout, simply redirect:

$ ./delete_from_empty.sh after_blank < input_file > before_blank

and you'll end up with two new files: after_blank and before_blank.