builtins

Builtins are commands that are available within the script runtime.

As with bash they do not require an external binary to run, the commands are compiled in to the shell executable.

cd

Change currenty directory

example:

cd /tmp

echo

Similar to bash echo.

example:

echo hello world

setenv

Similar to csh setenv.

example:

setenv LOGS_ON true

There are 3 variables that can be set without a value

• setenv date - sets the ${date} var to iso8601 date string, e.g. "2020-12-30"
• setenv time - sets the ${time} var to iso8601 time string, e.g. "13:59:30"
• setenv datetime - sets the ${datetime} var to iso8601 date string e.g. "2020-12-30T13:59:30"

unsetenv

Similar to csh unsetenv.

example:

unsetenv LOGS_ON

error

echo to stderr.

example:

error booting servers

setuid

Set current user id, setuid takes 1 or 2 numeric arguments, uid and optionally gid.

If the script is running as root this changes the processes effective user id, you cannot change back.

example:

setuid 1000 1000
/home/ubuntu/bin/server.sh

runas

Executes a process as a different user, the current process userid is not changed, this can be used as an alternative to /bin/su if the use is to step down privilidges from root. runas cannot step up privilidges to root.

example:

runas ubuntu /home/ubuntu/bin/server.sh

exec

Similar to bash exec but without redirects

exec /sbin/xtomp

spawn

Execute a process in the background, akin to bash's trailing &

example:

spawn /sbin/xtomp
spawn /usr/bin/rsyslog

reexec

Execute a process, if it ever terminates, restart it. This must be the last line of a script, it never returns.

reexec /bin/getty -L tty1 115200 vt100

respawn

Start a process that, if it ever stops, will be restarted. lxinitd supports up to 20 services.

example:

respawn /bin/getty -L tty1 115200 vt100
respawn /usr/bin/rsyslog