System information

An Introduction to Shells in General
Axis Communications AB provides NO support for application development of any kind. The information
here is provided "as is", and there is no guarantee that any of the examples shown will work in your
particular application.
Revision 1.02 October 2002 43
trap arg sigs
trap signals sigs and run arg on receipt
trap
list trapped signals
umask [n]
set the user file creation mask; show the current umask
wait [n]
wait for process pid n; wait for all processes
The shell also contains a programming language, which has the following operators and flow
control statements:
#
Comment. The rest of the line is ignored.
=
Assignment. Set a shell variable.
&&
Logical AND. Execute second command only if first succeeds.
||
Logical OR. Execute second command only if first fails.
(...)
Group. Execute enclosed commands before continuing.
for
For loop (for ... in ... do ... done)
case
Case statement ((case ... ) ... ;; ... esac)
esac
Case statement end
while
While loop (while ... do ... done)
do
Do/For/While loop start (do ... until ...)
done
For/While loop end
if
Conditional statement (if ... else ... elif ... fi)
in
For loop selection
then
Conditional statement start
else
Conditional statement alternative
elif
Conditional statement end
until
Do loop end
fi
Conditional statement end
See also:
echo(1), expr(1), pwd(1), true(1).
5.3 Additional Commands Available with Busybox
BusyBox combines tiny versions of many common UNIX utilities into a single small executable.
It provides minimalist replacements for most of the utilities you usually find in fileutils,
shellutils, findutils, textutils, grep, etc. BusyBox provides a fairly complete POSIX environment
for any small or embedded system. The utilities in BusyBox generally have fewer options than
their full-featured GNU cousins; however, the options that are included provide the expected
functionality and behave very much like their GNU counterparts.