sed，替换第一行的第一个匹配项

Question

my text looks like below

this This that
it It Its
my My Mine
this This that
it It Its
my My Mine

I want to replace the first line of the first occurrence match. eg. match the line which contains my then replace the line. I did

cat txt|sed "0,/my/c\my changed line" txt

The print off looks below, the first 2 line are trimmed.

my changed line
this This that
it It Its
my My Mine

if I run this cat txt|sed "s/my/changeline/" txt

The output is below

this This that
it It Its
changeline My Mine
this This that
it It Its
changeline My Mine

How can I get the result like below?

this This that
it It Its
changeline My Mine
this This that
it It Its
my My Mine

Answer 1

Using sed :

sed '0,/.*my.*/s//my changed line/' file

What this does, in the range of 0,/.*my.*/ it will replace the matched .*my.* with "my changed line".

An equivalent slightly easier to understand version of the same thing:

sed '0,/my/{/.*my.*/s//my changed line/}' file

Using awk the logic is slightly easier to understand:

awk '!/my/ || seen { print } /my/ && !seen { print "my changed line"; seen = 1 }' file

Answer 2

$ awk '/my/ && !f++{$0="changeline My Mine"} 1' file
this This that
it It Its
changeline My Mine
this This that
it It Its
my My Mine