Sed/Awk to delete second occurence of string - platform independent

Question

I\'m looking for a line in bash that would work on both linux as well as OS X to remove the second line containing the desired string:

Header
1
2
...
Header
10
1         


        

Answer 1

I would recommend using awk for this:

awk '!/^Header/ || !f++' file

This prints all lines that don't start with "Header". Short-circuit evaluation means that if the left hand side of the || is true, the right hand side isn't evaluated. If the line does start with Header, the second part !f++ is only true once.

$ cat file
baseball
Header and some other stuff
aardvark
Header for the second time and some other stuff
orange
$ awk '!/^Header/ || !f++' file
baseball
Header and some other stuff
aardvark
orange

Answer 2

This might work for you (GNU sed):

sed -i '1b;/^Header/d' file

Ignore the first line and then remove any occurrence of a line beginning with Header.

To remove subsequent occurrences of the first line regardless of the string, use:

sed -ri '1h;1b;G;/^(.*)\n\1$/!P;d' file

Answer 3

Since this is file-dependent and not line-dependent, awk can be a better tool.

Just keep a counter on how many times this happened:

awk -v patt="Header" '$0 == patt && ++f==2 {next} 1' file

This skips the line that matches exactly the given pattern and does it for the second time. On the rest of lines, it prints normally.