delete a line from a file containing the exact number and quit on the first find & delete

Question

I am trying to delete a numerical value once only from a file where there could be more than one instance of that value. file_input=

I need to delete '8' but only once and i want to keep '18'. The final result should be in file_output as such:

I tried sed '/8/d', grep -v -w '8' and awk '$1 !=8' but they all delete 8, 8, and 18.

How to replace '8' by a var such as $number as this function can be called to delete a different number when used? — user312288, Dec 28 '17 at 20:07
With a variable: `n="8"; sed '1,/^'"$n"'$/{/^'"$n"'$/d}' file` — Cyrus, Dec 28 '17 at 21:29

score 2 · Accepted Answer · answered Dec 28 '17 at 13:55

2

I suggest with GNU sed:

sed '1,/^8$/{/^8$/d}' file

Output:

From first line to line which contains only 8 (1,/^8$/) delete line which contains only 8 (/^8$/d).

answered Dec 28 '17 at 13:55

Cyrus

This works as I want even if I add 88 before the value 8. Wonderful, thanks. – user312288 Dec 28 '17 at 14:09
When you have to write the same code multiple times (e.g. `/^8$/` twice in this case), it means you should look for a different solution. – Ed Morton Dec 28 '17 at 15:27

score 1 · Answer 2 · answered Dec 28 '17 at 14:33

1

Here's the awk version

$ awk '!($1==8 && !c++)' ip.txt
2  
4  
18  
8  
10  
12  
14

$1==8 && !c++ check if first field is exactly 8, if so check whether c evaluates to false(c will get incremented and so won't be false next time)
- we don't want to print when this is true, hence the outer negation
this will work even if there are whitespaces around the first field, like in the given sample in question

answered Dec 28 '17 at 14:33

Sundeep

2

Ahem - double negative? `awk '$1==8 && !c++{next} 1' ip.txt` – Ed Morton Dec 28 '17 at 15:22

2 Answers2