CODEWITHSUNDEEP
bashgrep
jabk
jabk

Reputation: 1458

Multiple simultaneous patterns for grep

I need to see if user exists in /etc/passwd. I'm using grep, but I'm having a hard time passing multiple patterns to grep.

I tried 

if [[ ! $( cat /etc/passwd | egrep "$name&/home" ) ]];then
   #user doesn't exist, do something
fi

I used ampersand instead of | because both conditions must be true, but it's not working.

Upvotes: 0

Views: 384

Answers (2)

tripleee
tripleee

Reputation: 189387

Contrary to your assumptions, regex does not recognize & for intersection, even though it would be a logical extension.

To locate lines which match multiple patterns, try

grep -e 'pattern1.*pattern2' -e 'pattern2.*pattern1' file

to match the patterns in any order, or switch to e.g. Awk:

awk '/pattern1/ && /pattern2/' file

(though in your specific example, just "$name.*/home" ought to suffice because the matches must always occur in this order).

As an aside, your contorted if condition can be refactored to just

if grep -q pattern file; then ...

The if conditional takes as its argument a command, runs it, and examines its exit code. Any properly written Unix command is written to this specification, and returns zero on success, a nonzero exit code otherwise. (Notice also the absence of a useless cat -- almost all commands accept a file name argument, and those which don't can be handled with redirection.)

Upvotes: 0

Gilles Quénot
Gilles Quénot

Reputation: 185106

Try doing this :

$ getent passwd foo bar base

Finally :

if getent &>/dev/null passwd user_X; then
    do_something...
else
    do_something_else...
fi

Upvotes: 2

Related Questions