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About linux : Linux—Delete-all-lines-from-a-given-line-number

Question Detail

I am trying to delete a file’s contents from a supplied line number using sed. The problem is that sed isn’t accepting the variable I supply to it

line_num=$(grep -n "debited" file.csv | sed -n '2 s/:.*//p') && sed -i.bak "$line_num,$d" file.csv

The idea is to delete all lines from a file after & including the second occurence of the pattern.

I’m not stubborn with sed. Awk & perl could do too.

Question Answer

Seems like you want to delete the rest of the file after a second showing of a pattern (debited), including that line.

Then can truncate it, ising tell for the length of what’s been read up to that line

perl -e'while (<>) { 
    if ( ($cnt += /debited/) == 2 ) { truncate $ARGV, $len; exit } 
    $len = tell;
}' file

Here the $ARGV variable has the “current” file (when reading from <>). Feel free to introduce a variable with the pattern instead of the literal (debited), based on your context.

This can be made to look far nicer in a little script but it seems that a command-line program (“one-liner”) is needed in the question.

I always suggest ed for editing files over trying to use sed to do it; a program intended from the beginning to work with a file instead of a stream of lines just works better for most tasks.

The idea is to delete all lines from a file after & including the second occurence[sic] of the pattern


$ cat demo.txt
debited 12
debited 14
$ printf "%s\n" '/debited/;//,$d' w | ed -s demo.txt
$ cat demo.txt
debited 12

The ed command /pattern/;//,$d first sets the current line cursor to the first one that matches the basic regular expression pattern, then moves it to the next match of the pattern and deletes everything from there to the end of the file. Then w writes the changed file back to disk.

you’re doing lot’s of unnecessary steps, this will do what you want.

$ awk '/debited/{c++} c==2{exit}1' file

delete second occurrence of the pattern and everything after it.

To replace the original file (and create backup)

$ awk ... file > t && mv -b --suffix=.bak t file

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