Replace a particular pattern in a file

Shell Programming and Scripting
1

Hi ,
I have a requirement where i have this file

abcd
$$xyz=123
$$zef=789

$$mno=123
$$pqr=456

I need to replace $$pqr from 456 to a new value which will be present in a variable to me.
I am not aware of sed and awk functionality.
Can somebody please show me how to replace this 456 with a new value .

2

perl -e -pi s/456/'$var'/g infile

3

If pqr can have any numeric value you can use:

sed 's/\(^$$pqr=\)[0-9][0-9]*$/\1'"$VAR"'/' infile
4

alternative in sed..

sed '/$$pqr/s/[0-9]\+/'$VAR'/' inputfile > outfile
5

And another one with awk:

awk -v var=$variable -F= '/\$\$pqr/{$2=var}1' OFS=\= infile
6 
sed '/$$pqr=/'"s/=.*/=$var/" infile

sed "/\$\$pqr=/s/=.*/=$var/" infile
7

Or using Perl -

$
$ cat f42
abcd
$$xyz=123
$$zef=789
 
$$mno=123
$$pqr=456
$
$
$ typeset -x VAR="999"
$
$ # Perl one-liner to substitute the value
$ perl -lne 'if (/^(\$\$pqr=).*/){print $1,$ENV{"VAR"}} else {print}' f42
abcd
$$xyz=123
$$zef=789
 
$$mno=123
$$pqr=999
$
$

tyler_durden