BASH grep脚本

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

Answer 1

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

Answer 2

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'

Answer 3

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.