use SED to replace repeat statements

Shell Programming and Scripting
1

Hi
I need to write a script that read a input file that had same statement repeatedly to replace only 2nd & 5th time repeated statements (ex: This is UNIX forum) with another statement ( UNIX forum threads in Shell programming) with out modifying 1st,3,4th repeated statements. I am planning to do with sed. Any other available better approaches?

2

With no clue as to what your data looks like, I shall assume that yours is the simplest case where the string to be replaced occurs all by itself in a line.
Thus -

$
$ cat -n f3
     1  This is line 1. Some stuff here.
     2  This is UNIX. And some more stuff here. The weather's good.
     3  This is UNIX forum.
     4  Fourth line here.
     5  This is UNIX forum.
     6  And some more.
     7  This is UNIX forum.
     8  The line that does not have the target string.
     9  This is UNIX forum.
    10  Some filler stuff here.
    11  And finally -
    12  This is UNIX forum.
    13  The end.
$
$
$ ##
$ perl -lne 'BEGIN {$from="This is UNIX forum.";
>                   $to="==> UNIX forum threads in Shell programming <=="}
>            if (/$from/) {
>              $i++;
>              if ($i == 2 or $i == 5){print $to} else {print}
>            } else {print}' f3
This is line 1. Some stuff here.
This is UNIX. And some more stuff here. The weather's good.
This is UNIX forum.
Fourth line here.
==> UNIX forum threads in Shell programming <==
And some more.
This is UNIX forum.
The line that does not have the target string.
This is UNIX forum.
Some filler stuff here.
And finally -
==> UNIX forum threads in Shell programming <==
The end.
$
$

tyler_durden

3

Thanks Tyler..Got it