Bash-Beginners-Guide

posix
off
privileged
off
verbose
off
vi
off
xtrace
off
See the Bash Info pages, section Shell Built-in Commands->The Set Built-in for a description of each option.
A lot of options have one-character shorthands: the xtrace option, for instance, is equal to specifying set
-x.
3.6.2. Changing options
Bash Guide for Beginners
Shell options can either be set different from the default upon calling the shell, or be set during shell
operation. They may also be included in the shell resource configuration files.
The following command executes a script in POSIX-compatible mode:
willy:~/scripts> bash --posix script.sh
For changing the current environment temporarily, or for use in a script, we would rather use set. Use - (dash)
for enabling an option, + for disabling:
willy:~/test> set -o noclobber
willy:~/test> touch test
willy:~/test> date > test
bash: test: cannot overwrite existing file
willy:~/test> set +o noclobber
willy:~/test> date > test
The above example demonstrates the noclobber option, which prevents existing files from being
overwritten by redirection operations. The same goes for one-character options, for instance -u, which will
treat unset variables as an error when set, and exits a non-interactive shell upon encountering such errors:
willy:~> echo $VAR
willy:~> set -u
willy:~> echo $VAR
bash: VAR: unbound variable
This option is also useful for detecting incorrect content assignment to variables: the same error will also
occur, for instance, when assigning a character string to a variable that was declared explicitly as one holding
only integer values.
One last example follows, demonstrating the noglob option, which prevents special characters from being
expanded:
willy:~/testdir> set -o noglob
willy:~/testdir> touch *
willy:~/testdir> ls -l *
-rw-rw-r-- 1 willy willy 0 Feb 27 13:37 *
Chapter 3. The Bash environment 54