bash script grep the etc file for user information - bash

Question

I am trying to write a script in bash to read in arguments (usernames) and then return information about that username by searching the /etc/passwd file. I am not the root on the server that I am scripting this on, but I don't need to be. Here is the code that I have so far, but I dont think I am using the grep command right.
#!/bin/bash
if [ $# -eq 1 ]; then #if num of args =1; then continue on
UNAME=$1 #set arg to var UNAME
grep UNAME=$(grep $/etc/passwd)
if [ $UNAME == /etc/passwd ]; then #if UNAME exists then display info below
echo "-------------------------------------------"
echo "Username: $(grep UNAME/etc/passwd/ $f1) "
echo "User ID (UID): $(grep UNAME/etc/passwd/) "
echo "Group ID (GID): $(grep UNAME/etc/passwd/) "
echo "User info: $(grep UNAME/etc/passwd/) "
echo "Home directory: $(grep UNAME/etc/passwd/) "
echo "Command shell: $(grep UNAME/etc/passwd/) "
echo "-------------------------------------------"
else #if UNAME is nonexistant then display this error message
echo "-------------------------------------------"
echo ""$UNAME" does not exist."
echo "-------------------------------------------"
fi
fi
if [ $# -eq 0 ]; then #if num of args =0; then display this
echo "Not enough arguments provided."
echo "USAGE: $0 <user_name> [user_name] ..."
exit 1
fi

Answer 1

You're doing too much. grep is the wrong tool for the type of parsing you are trying to do. The solution given here is pretty sloppy since it reads the passwd file once for each user you are querying instead of reporting everything in one pass, but it's not unreasonable:
#!/bin/sh
for UNAME; do
while IFS=: read login passwd uid gid name home shell; do
if test "$login" = "$UNAME"; then
echo "-------------------------------------------"
echo "Username: $login"
echo "User ID (UID): $uid"
echo "Group ID (GID): $gid"
echo "User info: $name"
echo "Home directory: $home"
echo "Command shell: $shell"
echo "-------------------------------------------"
continue 2
fi
done < /etc/passwd
echo "No entry for user $UNAME" >&2
done

Answer 2

Before I get to the explanation, here is how I would have written your script:
cat ./test.sh
#!/bin/bash
UNAME=${1} #set arg to var UNAME
if [ -z ${UNAME} ]; then #if no argument is provided; then display this
echo "Not enough arguments provided."
echo "USAGE: $0 <user_name>"
exit 1
fi
if grep ${UNAME} /etc/passwd >/dev/null; then #if UNAME exists then display info below
echo "-------------------------------------------"
echo "Username: $(awk -F ':' -v uname=${UNAME} '$0 ~ uname {print $1}' /etc/passwd)"
echo "User ID (UID): $(awk -F ':' -v uname=${UNAME} '$0 ~ uname {print $3}' /etc/passwd)"
echo "Group ID (GID): $(awk -F ':' -v uname=${UNAME} '$0 ~ uname {print $4}' /etc/passwd)"
echo "User info: $(awk -F ':' -v uname=${UNAME} '$0 ~ uname {print $5}' /etc/passwd)"
echo "Home directory: $(awk -F ':' -v uname=${UNAME} '$0 ~ uname {print $6}' /etc/passwd)"
echo "Command shell: $(awk -F ':' -v uname=${UNAME} '$0 ~ uname {print $7}' /etc/passwd)"
echo "-------------------------------------------"
else #if UNAME is nonexistant then display this error message
echo "-------------------------------------------"
echo "\"${UNAME}\" does not exist."
echo "-------------------------------------------"
fi
Explanation:
if can use grep directly to check for the existence of
your argument in passwd
UNAME= is how arguments are assigned, not
called - they are called with the $ - for example $UNAME
/etc/passwd is an absolute file name and not an argument, thus
$/etc/passwd doesn't mean anything to bash
argument=$(any old bash command) is telling bash that you want to
assign the output of "any old bash command" to "argument", so $()
has to contain a command with output for "argument" to be assigned
anything.
the >/dev/null sends the output of grep to the waste basket because we only care at this point whether or not it's successful so that if knows what to do
grep works like this: grep <the thing you want to find> <file> (note that spaces matter and to use "" if you want to include spaces in your search)
to get specific fields, awk is more useful. awk -F':' tells awk that I want : to define my field separators; -v uname=${UNAME} passes my argument to awk; within awk, $0 ~ uname checks the line for my argument (like grep); and {print $1} prints the first field, and so on
Also consider the limitation of partial matches. If, for example, I have a user JSmith and Smith, searching Smith will return both. This can be addressed with regex but will add a great deal of complexity to the script.
Here is a version with lighter awk usage which works with multiple arguments:
#!/bin/bash
for username; do
if grep ${username} /etc/passwd >/dev/null; then #if username exists then display info below
echo "---------------------------------------"
awk -F':' -v uname="${username}" '\
$0 ~ uname \
{print " Username: "$1\
"\n User ID (UID): "$3\
"\n Group ID (GID): "$4\
"\n User info: "$5\
"\n Home directory: "$6\
"\n Command shell: "$7}' /etc/passwd
echo "---------------------------------------"
else #if username is nonexistant then display this error message
echo "---------------------------------------"
echo "\"${username}\" does not exist."
echo "---------------------------------------"
fi
done
if [ -z ${1} ]; then #if no argument is provided; then display this
echo " Not enough arguments provided."
echo " USAGE: $0 <user name>"
exit 1
fi
*Credit to William Pursell for explaining the for loop

Answer 3

The best tool to read databases such as passwd is getent. This will fetch entries from a database supported by Name Service Switch Libraries. If you really need to limit reading the files databases, you can tell getent to use files database with -s files.
Your code is unnecessarily long. Fetching a record and parsing them into multiple variables should be enough.
#!/bin/bash
if [ $# -eq 1 ]; then #if num of args =1; then continue on
if IFS=: read username ignore uid gid gecos home shell < <(getent -s files passwd $1); then
echo "-------------------------------------------"
echo "Username: $username"
echo "User ID (UID): $uid"
echo "Group ID (GID): $gid"
echo "User info: $gecos"
echo "Home directory: $home"
echo "Command shell: $shell"
echo "-------------------------------------------"
else #if $1 is nonexistant then display this error message
echo "-------------------------------------------"
echo "'$1' does not exist."
echo "-------------------------------------------"
fi
fi
if [ $# -eq 0 ]; then #if num of args =0; then display this
echo "Not enough arguments provided."
echo "USAGE: $0 <user_name> [user_name] ..."
exit 1
fi