Use sed to replace part of a string

bashsed

I am planning to replace certain strings in a file; so I am using sed.

I would like to have the string replaced, while instead, sed read the string and append the text in the middle of the string.

Example:

string in myfile : user=blabla
string that I want to obtain: user=bob

so I run sed in this way, to have it to search for the "user=" string, and replace it with "user=bob"

sed -i 's/user=*/user=bob/' myfile

What I get is 

user=bobblabla

Basically sed think that I want to replace just that part, while I want to replace the whole string with the new string. I thought that the * would tell sed to consider anything coming after, but it does not work.

Since I do not know what the "blabla" will be, I can't put it in the sed command. How do I tell sed to find a string that start with "user=" and replace the whole string with the new one?

Best Answer

You seem to be confusing shell patterns with regular expressions. In a shell pattern, * means zero or more of any character. In a regular expression, which is what sed expects in its patterns, * means zero or more of the previous atom. In your example, that atom is the =. So, sed is searching for user followed by zero or more = and replacing the matching string with user=bob. The pattern you want is user=.*, which is user= followed by any character (.) zero or more times, making your sed command:

sed -i 's/user=.*/user=bob/' myfile
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