如何从文本文件中的第一个空行开始删除所有行？

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: ABC
2: DEF
3:
4: GHI

Line 3 and 4 should be removed and the remaining content should be saved in a new file.

Answer 1

使用GNU sed ：

sed '/^$/Q' "input_file.txt" > "output_file.txt" 

Answer 2

With AWK :

$ awk '/^$/{exit} 1' test.txt > output.txt

Contents of output.txt

$ cat output.txt 
ABC
DEF

Walkthrough: For lines that matches ^$ (start-of-line, end-of-line), exit (the whole script). For all lines, print the whole line -- of course, we won't get to this part after a line has made us exit.

Answer 3

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.

Answer 4

Perl version

 perl -e '
        open $fh, ">","stuff";  
        open $efh, ">", "rest_of_stuff"; 
        while(<>){
           if ($_ !~ /\w+/){
                 $fh=$efh;
           } 
           print $fh $_;
         }
            ' demo

This creates two output files and iterates over the demo data. When it hits a blank line, it flips the output from one file to the other.

Creates

stuff:

ABC
DEF

rest_of_stuff:

<blank line>
GHI

Answer 5

Another awk would be:

awk -vRS= '1;{exit}' file

By setting the record separator RS to be an empty string, we define the records as paragraphs separated by a sequence of empty lines. It is now easily to adapt this to select the nth block as:

awk -vRS= '(FNR==n){print;exit}' file

There is a problem with this method when processing files with a DOS line-ending (CRLF). There will be no empty lines as there will always be a CR in the line. But this problem applies to all presented methods.