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Replace value of a variable in a file through script using sed

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# 1  
Old 07-08-2012
Replace value of a variable in a file through script using sed
Hi,

I am trying to replace the value of a variable in a file through another script.

Example:
Filename : abc.txt contents:
a=10
b=20
c=30

Need to change the value of, say, b - Tried using the following:
Code:
sed "s/${b}/15/g" abc.txt

Have tried various forms of sed (with single quotes, without quotes, with -e option, etc) but getting the same error with all:
Code:
sed: -e expression #1, char 0: no previous regular expression

Smilie

Thanks for any help in advance Smilie
# 2  
Old 07-08-2012
Quote:
Originally Posted by rituparna_gupta
Code:
sed "s/${b}/15/g" abc.txt

Have tried various forms of sed (with single quotes, without quotes, with -e option, etc) but getting the same error with all:
Code:
sed: -e expression #1, char 0: no previous regular expression

You are getting that error because the shell variable, ${b}, is unset or null. After its expansion, the sed command becomes s//15/g. In sed, an empty regular expression is equivalent to the most recently used regular expression. Since there is none, you get that error.

Regards,
Alister
# 3  
Old 07-08-2012
Thanks Alister...

Is there any way this can be overcome - so that I can have variable in the file referenced directly
# 4  
Old 07-08-2012
how about:
Code:
sed "s/^b=.*/b=${b}/" abc.txt

This User Gave Thanks to Chubler_XL For This Post:
rituparna_gupta
# 5  
Old 07-09-2012
It worked - Thanks Chubler_XL Smilie
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