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Bash script to change user


 
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# 1  
Old 04-08-2020
Bash script to change user

So, I need to write bash file that will
1) get name of the user you want to switch to
2) check if there is such user
3) check length of entered name of user
4) and change user
My script looks like this
Code:
read $user_name
if ( ! [[ $(cat /etc/passwd | grep $user_name) ]] ) then echo "error. There is no such user" exit 1 fi
if (( $(expr length $user_name) >= 30 ))
then echo "error" exit 1 fi
sudo su $user_name 
exit 0

But if I enter existing user it shows error message
Where is my mistake?

Moderator's Comments:
Mod Comment
Please use code tags when posting data and code samples!

Last edited by vgersh99; 04-08-2020 at 01:20 PM.. Reason: code tags, please!
# 2  
Old 04-08-2020
you didn't provide the specific like OS, preferred shell etc...
just guessing - YMMV:
Code:
#!/bin/ksh

read $user_name
if [ $(grep $user_name /etc/password) ]; then
    :
else
   echo "error. There is no such user" 
   exit 1
fi
if [ ${#user_name} -ge 30 ]; then
    echo "error" 
    exit 1
fi
sudo su $user_name 
exit 0

# 3  
Old 04-08-2020
Quote:
Originally Posted by vgersh99
you didn't provide the specific like OS, preferred shell etc...
just guessing - YMMV:
Code:
.
.
.

 read $user_name
if [ $(grep $user_name /etc/password) ]; then
.
.
.

Shouldn't that be
Code:
read user_name                            # no "$", no expansion
if grep $user_name /etc/passwd; then ...  # no "[" (test) command, no "command substitution" - use grep's exit code immediately

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