[SOLVED] sed 2nd occurance is not changing

arun natarajan · 04-16-2016, 05:50 AM

Hi,

In sed, am not able to replace the 2nd occurrence as expected. Why ??
[root@server awk]# cat marks
1) Amit Physics 80
2) Rahul Physics 80
3) Shyam 87
4) Kedar English 85

[root@server awk]# sed -e 's/80/90/2' marks
1) Amit Physics 80
2) Rahul Physics 80
3) Shyam 87
4) Kedar English 85

Also, in sed, when not using the option 'g', hope it should replace only in 1st occurrence, but for me its changing in all occurrence. Why ??

[root@server awk]# sed -e 's/80/100/' marks
1) Amit Physics 100
2) Rahul Physics 100
3) Shyam 87
4) Kedar English 85

Waiting for solution for both queries.

syg00 · 04-16-2016, 06:05 AM

sed works on records. The number refers to the "nth" occurrence in each (matching) record. The "g" is a global change in each (matching) record.

grail · 04-16-2016, 10:49 AM

You seem to be thinking of the second occurrence based on each line being an occurrence, but sed sees it as the number of occurrences on a single line:

Code:

sed -e 's/80/90/2' <<<'1) Amit 80 Physics 80'
1) Amit 80 Physics 90

arun natarajan · 04-16-2016, 10:53 AM

Thanks grail, it worked as u said.

HMW · 04-16-2016, 10:56 AM

Quote:

Originally Posted by arun natarajan

Also, in sed, when not using the option 'g', hope it should replace only in 1st occurrence, but for me its changing in all occurrence. Why ??

[root@server awk]# sed -e 's/80/100/' marks
1) Amit Physics 100
2) Rahul Physics 100
3) Shyam 87
4) Kedar English 85

Waiting for solution for both queries.

If you want to stop after the FIRST change. Use a solution similar to this:

Code:

echo "foo bar
foo bar
foo bar" | sed '0,/bar/{s/bar/NAPALM DEATH/}'
foo NAPALM DEATH
foo bar
foo bar

As you can see, only the first 'bar' is changed. Only works with GNU sed which I assume you have.

Best regards,
HMW