Scripting - Iterating Numbers Using a While Loop (newusers command) - linux

Question

I am working on a script where I want to iterate between the numbers 1 to 15, but want it shown as 01 02 03 ... 13 14 15. Essentially what I am trying to do is add 15 users using the newusers command and using this script as < to the command. newusers needs to be in this format:
pw_name:pw_passwd:pw_uid:pw_gid:pw_gecos:pw_dir:pw_shell
Basically, it should look like this when I run the script with arguments =
cstuser01:EzVlK9Je8JvfQump:1001:1001:CST8177 user:/home/cstuser01:/bin/bash
cstuser02:EsKOfvhgnWpiBT6c:1002:1002:CST8177 user:/home/cstuser02:/bin/bash
cstuser03:qzQuR5vRgxdzY6dq:1003:1003:CST8177 user:/home/cstuser03:/bin/bash
I got most of it working but I am getting the error below:
./15users.sh: 57: ./15users.sh: Illegal number: 08
Here is my script so far (I took out a couple sections with error checking) =
#!/bin/sh -u
PATH=/bin:/usr/bin ; export PATH
umask=022
#num=1 (this variable is needed depending on which loop I use below)
user=$prefix"user"
uid=1001
gid=$uid
home=/home/$user
shell=/bin/bash
#echo "pw_name:pw_passwd:pw_uid:pw_gid:pw_gecos:pw_dir:pw_shell"
#PASSWD=$(openssl rand -base64 12)
I originally had this but ran into a few problems:
while [ $NUM -le 15 ] ; do
if [ $NUM -lt 10 ] ; then
NUM=0$NUM
fi
echo "$USER$NUM:$(openssl rand -base64 12):$UID:$GID:$GECO:$HOME$NUM:$SHELL"
UID=$(( UID + 1 ))
GID=$(( GID + 1 ))
NUM=$(( NUM + 1 ))
done
A friend of mine suggested this, it works perfectly fine. But I am trying to future proof this thing. What if I have a 100 or 1,000 users to add.
for NUM in 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 ; do
echo "$USER$NUM:$(openssl rand -base64 12):$UID:$GID:$GECO:$HOME$NUM:$SHELL"
done
This didn't work:
for num in {01..15} ; do
i=09
echo "$(( 10#$num + 1 ))"
10
done
I then tried this getting a syntax error =
./15users.sh: 50: ./15users.sh: Syntax error: Bad for loop variable
for (( num=1; num<=15; num++ )) ; do
printf "%02d\n" $num
done
I tried this as well but seq prints vertically not horizontally:
#iterate=$(seq -w 1 15)
for $iterate ; do
echo "$user$num:$(openssl rand -base64 12):$uid:$gid:$geco:$home$num:$shell"
done

Answer 1

To loop over 01 to 15, it is much simpler to use brace expansion:
$ for num in {01..15}; do echo "$num"; done
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
In bash, by default, numbers beginning with 0 are octal. Since 08 and 09 are illegal as base-8 numbers, they will cause an error. To avoid that, explicitly specify the base:
$ i=09; echo $(( 10#$i + 1 ))
10
The expression 10#$i tells bash to interpret $i as a base-10 number.
Do NOT use all caps for your script variables. The system uses all caps and you don't want to accidentally overwrite a system variable.
In the case of UID, it is a read-only bash variable. Attempts by your script to assign UID will fail. Use lower or mixed-case for your script variables.
Another example of the all caps problem is $HOME. Note that the following code works:
$ openssl rand -base64 12
1bh9+dp+Ap7xFIBB
But the following fails:
$ (HOME=/home/user; openssl rand -base64 12)
zceZeWsQGpohTPvv
unable to write 'random state'
Apparently, openssl expects to have write-access to $HOME.
Assigning HOME to a non-existent directory causes an error.
So, again, do not all all caps for your script variables.

Answer 2

I won't try to diagnose your error message, but you're over-complicating what you're trying to achieve.
for i in {01..15}; do echo $i; done
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15

Answer 3

Bash supports C style loops as well:
$ for (( i=1; i<=15; i++ )); do printf "%02d\n" $i; done
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
Just use printf with the flag to print leading 0 and you have your output.

Answer 4

Since it hasn't been mentioned yet:
seq -w 1 15
seq -w 1 15 | while read num; do echo "n=$num"; done