Perl : how to modify a file without generate a temporary file

Shell Programming and Scripting
1

Hi All,

I have a file like below, how can i insert one line after line 1 without using a temporary file in perl?

line 1
line 2
line 3

expected result

line 1
new line <---insert here
line 2
line 3
2

Hi

[root@gpr ~]# cat a
abc
efg
hij
[root@gpr ~]# perl -i -pne  'if($.==2){print "more\n"}' a
[root@gpr ~]# cat a
abc
more
efg
hij
[root@gpr ~]#

Guru.

3

thanks very much for your reply.
with inplace file edit, it is ok for this easy case.
but my requirement is a little bit complicated:

1> rather than directly insert lines in original file, still need to open file to read and check some key word

2> if key words found, print the key words

3> if key words not found, insert into file

example

original file

[books]
java = 30$
oracle = 20$
[tools]
Ultraedit = 100$
Eclipse = 200$

supposed the perl script is named as conf.pl, -s option is for section, -k option is for key, -v option is for value

1> conf.pl -s books -k java
    print 30$

2> conf.pl -s books -k perl -v 40$
    append line 
    perl = 40$ 
    after line 
    oracle = 20$

3> conf.pl -s cds -k english -v 100$
    append 
    [cds]
    english = 100$

So basically the case is modify file content on hot at any time if meet or not-meet any condition.