Joe, a user, creates a short shell script, shortscript.sh, and saves it in his home directory with default permissions and paths. He then attempts to run the script by typing ./shortscript.sh, but the

When a file is created with default permissions, the execute bit is absent, so invoking ./shortscript.sh fails with a 'Permission denied' error. The command chmod u+x shortscript.sh adds the execute (x) permission for the owning user (u), which is the direct fix that enables Joe to run the script using the ./shortscript.sh syntax.

source ./shortscript.sh is an alternative invocation that reads and executes the file in the current shell without requiring execute permission, but it is not a setup command that enables the ./shortscript.sh syntax to succeed - it bypasses rather than fixes the permission problem.

chmod 155 sets permissions to --x r-x r-x, which denies read permission to the owner, preventing the shell from reading and interpreting the script file when it is executed.

chgrp changes the group ownership of the file but does not modify any permission bits, so it would not grant the execute permission needed to run the script.