Extracting all group members

a2326 · 11-16-2012, 09:08 AM

Hello,
I want to extract all members of a group, but I don't get the output that I want:

Code:

GROUP=groupname
cat /etc/group | grep --regex "^"$GROUP":.*" | awk -F:, '{print $4}'

I would like to have an output with one user per line like:
username1
username3
....

Is it good practice in shell script to save such data in a file and then read the file when the data shall be used or are there better techniques? Thanks.

druuna · 11-16-2012, 09:30 AM

Quote:

Originally Posted by a2326

Hello,
I want to extract all members of a group, but I don't get the output that I want:

Code:

GROUP=groupname
cat /etc/group | grep --regex "^"$GROUP":.*" | awk -F:, '{print $4}'

I would like to have an output with one user per line like:
username1
username3
....

Have a look at this:

Code:

awk -F: '/^'$GROUP'/ { gsub(/,/,"\n",$4) ; print $4 }' /etc/group

Quote:

Is it good practice in shell script to save such data in a file and then read the file when the data shall be used or are there better techniques? Thanks.

I'm not 100% sure what it is you are asking. If you are talking about saving the output of one command to use it as input for a second command then the answers is: No, try to avoid this if possible.

a2326 · 11-16-2012, 09:48 AM

That works, thank you :-) To be more precise: Is it a good choice to store the extracted data set in a file or is better to store the data in some kind of shell script data structure? E.g., in Java or C++ you often store file data in arrays or lists and then you just loop through this data structure. However, transferring Java way of thinking to shell scripting is often not possible that's why I am asking this question.

druuna · 11-16-2012, 09:57 AM

Quote:

Originally Posted by a2326

To be more precise: Is it a good choice to store the extracted data set in a file or is better to store the data in some kind of shell script data structure? E.g., in Java or C++ you often store file data in arrays or lists and then you just loop through this data structure. However, transferring Java way of thinking to shell scripting is often not possible that's why I am asking this question.

That all depends on the data and what it is you need/want to do with it (same is probably true for higher programming languages).

Bash, awk and perl (to name just 3) can use array's if needed. Do check the specific documentation, I'm sure that array's are handled differently then in Java or C(++).

These might help:

Bash resources:

Bash Frequently Asked Questions
Bash Guide for Beginners (array's are briefly mentioned)
Advanced Bash-Scripting Guide (array's are mentioned)
Bash Pitfalls

Sed/Awk resources:

GNU sed, a stream editor
The GNU Awk User's Guide (array's are mentioned)