Use GNU passwd
stdin flag.
From the man
page:
--stdin This option is used to indicate that passwd should read the new password from standard input, which can be a pipe.
NOTE: Only for root user.
Example
$ adduser foo
$ echo "NewPass" |passwd foo --stdin
Changing password for user foo.
passwd: all authentication tokens updated successfully.
Alternatively you can use expect
, this simple code will do the trick:
#!/usr/bin/expect
spawn passwd foo
expect "password:"
send "Xcv15kl\r"
expect "Retype new password:"
send "Xcv15kl\r"
interact
Results
$ ./passwd.xp
spawn passwd foo
Changing password for user foo.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.