Shell Programming and Scripting

# cat file
12
13
14
15

# sed '/12/d' file
13
14
15

sed '4s/.*/this is the new line\n&/' infile
one
two
three
this is the new line
four
five

# cat in
1
2
3
4

# export n=3
# export s="aaa"
# awk -vn=$n -vs=$s 'NR==n{print s}1' in
1
2
aaa
3
4

$ cat file1
a
b
c
d

$ sed '3 i\
new line goes here' file1
a
b
new line goes here
c
d

# or
$ sed '3 a\
new line goes here' file1
a
b
c
new line goes here
d

sed "3s/^/$line\n/" infile

#!/usr/bin/perl

while (<>) {
if ($. == $linenum ) { print "test line \n"; }
print $_;
}

#!/bin/sh

linecount=`cat test1.txt | wc -l`
linetoinsert="test line to insert"
linenumber=4

linecount_head=`expr $linenumber - 1`
linecount_tail=`expr $linecount - $linenumber + 1`

head -$linecount_head test1.txt;echo $linetoinsert;tail -$linecount_tail test1.txt