search a line and insert string into specific at position

Shell Programming and Scripting
1

Hi, guys. I have one question:

How can I search for a line with certain string in it and then insert a string into this line?
For example:

There is a file called shadow, the contents of it are below:

**************************
...
yuanz:VIRADxMsadfDF/Q:0:0:50:7:::
sherrys:ASdfe#$DfdadfFAd:0:0:50:7:::
brownj:ADdfTRMnD$%3dfa:0:0:50:7:::
...
**************************

A variable called $user, another variable called $string. I want to search the line which has $user in it, and add $string at the beginning of the second column. If $user is brownj, and $string is STRING_, then the line will be:

brownj:STRING_ADdfTRMnD$%3dfa:0:0:50:7:::

I use the following code, but it doesn't work

sed 's/^$user:/$user:$string/' shadow

Can anybody help me with this?

Thank you very much for your time in advance

-Keyang

2

it is advisable not to change your shadow file like that. (however its still possible). change the password using commands such as passwd, usermod ...

3

hi, ghostdog74.

I am not changing the password in this way, I want to suspend the user, I add a string to the encrypted password, so the user is not able to login. I am new to Linux, so I do not really know whether or not this is a good practice. And as a practice, I could not user command like "passwd" and "usermod". Still, thanks for your reply.

@general:
Does anybody can help me with this question?

Thank you very much for your time in advance

-Keyang

4

please check the passwd and usermod man page. there are options to "suspend" user.

5

awk again :wink:

awk '{FS=OFS=":"}/brownj/{$2="STRING_"$2}1' shadow
6

Hi, ghostdog74.

I am not supposed to use commands like suspend and passwd for this exercise. :frowning:

Still, thanks for the reply. :slight_smile:

-Keyang

7

Hi, Dan.

Thanks for answering again! I will try it out.

But can you tell me what is wrong with my code? if I don't use variables in my code, it works well. For example:

sed 's/^brownj:/brownj:STRING_/' shadow

It will find brownj and replace it with brownj:STRING_.

Thanks for your time in advance

-Keyang

8

Hi, Dan.

The code doesn't work for my case, the same problem I met before with my code. It seems that I cannot pass any variable to awk and sed.

@general:

Is there anybody know how to solve this problem?

Thanks for your time in advance

-Keyang

9 
sed "s/^$user:/$user:$string/" shadow

awk 'BEGIN {FS=OFS=":"}$1 == usr {$2=str}1' usr="${user}" str="${string}" shadow
10

Hi, Vgersh99.

Thank you very much for your reply!

-Keyang