BASH grep script

Question

I am trying to work on a bash script that checks for a username in the argument of the script and then outputs the relevant lines from the /etc/passwd and /etc/group files (not the /etc/shadow file). Currently, I am utilizing a if then else loop to check the contents of the /etc/* directory and output the relevant information. My intention was to output simple text line if a match user is not found in the two files, thus a null value. However, it is outputting information that is totally incorrect for what I am looking for.As a new user to BASH, and linux is general, I am sure there are some glaring issues right away. However, I am trying to learn.

Any help with the code of my script or a point in the right direction would be greatly appreciated. Thank you.

#! /bin/bash                                                              


USERLOOK='grep -h $USERID ~/etc/* | grep :x:'                       

grep $1 ~/etc/*                                                     
if [ -z $1 ]; then                                                        
    echo "User not found."                                            
else                                                                      
    echo "$USERLOOK"                                                  
fi                                                                        
exit 0

Question not clear? You wish to enter the username as an argument to script say ./script user_to_check? — sjsam
– sjsam, Commented Jul 17, 2016 at 19:31
@sjsam Yes, I want to have the script function where I input ./script user_to_check. If the username is found, I want to output all lines where it was found, that was my reasoning for using grep. However, if the username was not found, I wanted to echo that. — NewBashUser226
– NewBashUser226, Commented Jul 17, 2016 at 19:47
@Cyrus Thanks for the link. I have tried spellcheck a couple of times with various iterations of this script. While some return no errors, the output was never really what I was looking for. Thanks for the suggestion though. — NewBashUser226
– NewBashUser226, Commented Jul 17, 2016 at 19:57

jchavannes · Accepted Answer · 2016-07-17 19:57:52Z

2

Finds any lines in /etc/passwd or /etc/group that contain the inputted username:

#!/bin/bash

USERLOOK=$(grep -h "$1" /etc/passwd /etc/group)

if [ -z "$1" ] || [ -z "${USERLOOK}" ]; then
    echo "User not found."
else
    echo "$USERLOOK"
fi

edited Jul 17, 2016 at 19:57

answered Jul 17, 2016 at 19:32

jchavannes

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6 Comments

λuser Over a year ago

the :x: won't work for /etc/shadow, and anyway you should anchor the search to the beginning of the line, e.g. "^$1:"

Мона_Сах Over a year ago

You may wish to replace the legacy backticks with $()

NewBashUser226 Over a year ago

Thank you for the response. This definitely works better that what I initially have, however, I was trying to return all lines from both files that contain the username that was input in the script arguments. Also, I do see some syntax errors that I made based on this script, so thank you for that as well.

NewBashUser226 Over a year ago

Also, am I correct in thinking that the first line of the IF statement is just looking for a blank argument, or would that function the same if the username is not found in either of the two files?

jchavannes Over a year ago

Okay, I saw the :x: in your question and figured you were looking for only those lines, I've updated the script to include all lines and also check for empty input.

|

Мона_Сах · Accepted Answer · 2016-07-17 20:01:11Z

1

I want to have the script function where I input ./script user_to_check. If the username is found, I want to output all lines where it was found... However, if the username was not found, I wanted to echo that.

It can be as simple as

#!/bin/bash
grep "^${1}:" /etc/passwd   /etc/group
[ $? -ne 0 ] && echo "User : ${1} not found"

As the user name appears in the beginning in both /etc/passwd & /etc/group we placed a ^ in grep to match stuff at beginning and by tradition a : appears just after the username.

Run the script as

./script 'username'

edited Jul 17, 2016 at 20:01

answered Jul 17, 2016 at 19:36

Мона_Сах

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7 Comments

λuser Over a year ago

use "^$1:" else you could get a user foobar when calling ./script foo

NewBashUser226 Over a year ago

Thank you for the response. This does return the first username value. However, I am trying to return all lines the contain the username that was input, thus my initial reasoning for utilizing grep.

NewBashUser226 Over a year ago

@mona_sax Once again, thanks for the help. I just typed out that script with a username that I know is present in the file, but it still returns a not found. In another response, I clarified a little more with what I was trying to do with this script: " I want to have the script function where I input ./script user_to_check. If the username is found, I want to output all lines where it was found, that was my reasoning for using grep. However, if the username was not found, I wanted to echo that."

Мона_Сах Over a year ago

@NewBashUser226 : See the update please. Pls gimme n update if this helped?

NewBashUser226 Over a year ago

@mona_sax Thanks for the help. Your script actually helped me research a couple more topics and I will look into your methodology versus mine as well. However, I believe the script that jchavannes posted answers my question and utilizes code that is closer to my new user skill level.

|

Ed Morton · Accepted Answer · 2016-07-17 21:05:32Z

0

Stop, you're thinking about this all wrong.

A UNIX shell is an environment from which to call UNIX tools with a language to sequence those calls, that is all. The general purpose UNIX tool to manipulate text is awk. So if you need to look for text in a file and have control logic to do anything with it, that should be an awk script, not a shell script. Shells role is to just call awk, something like this:

awk -v user="$1" '
$0 ~ user { line = $0 }
END { print (line != "" ? line : "User not found") }
' /etc/passwd /etc/group

but note that it's trivial with awk to focus the search on just one field, even a different field for each file, unlike how difficult that is in general with grep.

answered Jul 17, 2016 at 21:05

Ed Morton

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