Shell Programming and Scripting

At the moment, I'm trying to do the following:

1. Have sed read the first line of a file

Example (file1.x):

Code:

5

2. Replace that first line with a new first line, which would read

Code:

5=newvariable

3. Have that information placed into file2.y

Unfortunately, I'm having a problem. Sed keeps giving me some kind of command error.

Code:

$ sed 's/'"$1"'/'"$1"'=newvariable/g' file1.x > file2.y
sed: -e expression #1, char 0: no previous regular expression

Why is this happening?

please try this out,

sed 's/'$var1'/'$var1'='$var2'/g' file1.x > file2.y

Those single quotes would prevent variable expansion. Drop them and use the double quotes.

Code:

sed "s/$var1/$var1=$var2/g" file1.x > file2.y

Hey Agent,

use
sed 's/$var1/$var1=$var2/g' file1.x > file2.y

Regards
Nidhi

Agent,i think we can't use the special variable $1 to access the first field of the line read from file as in awk.These variables can only be used after a regular expression match was done in sed.See the below code

Code:

sed -ne '/5/'{s/$1/New/p} file.x

The above code will match for '5' in the readed line and then that matched expression was replaced using $1 variable in the curly braces with 'New' as an action.

In your code,since there wasn't a regex usage the $1 variable is undefined and thereby shows error.

With Regards
Dileep Pattayath