12-04-2004
They are other integers that relate to files. Some programs are too complex to fit into a stdin/stdout model. Some scripts simply need more stuff as well. A contrived example:
exec 3> john.out
exec 4>paul.out
exec 5>george.out
exec 6>ringo.out
echo harrison >&5
echo lennon >&3
With these echo statements, something like >&3 really means 1>&3 which means send fd 1 into whatever fd 3 is pointing to. Nobody actually writes to 3 in this case. 3 is kind of a placeholder. With the korn shell, you can do
print -u6 starr
where the -u6 says to actually use fd 6. And you might write a c program with statements like:
write(4, "mccartney", 10);
With a program like that, you may need to connect something to fd 4 if the program itself doesn't do it.
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LEARN ABOUT DEBIAN
escape
escape(1) Mail Avenger 0.8.3 escape(1)
NAME
escape - escape shell special characters in a string
SYNOPSIS
escape string
DESCRIPTION
escape prepends a "" character to all shell special characters in string, making it safe to compose a shell command with the result.
EXAMPLES
The following is a contrived example showing how one can unintentionally end up executing the contents of a string:
$ var='; echo gotcha!'
$ eval echo hi $var
hi
gotcha!
$
Using escape, one can avoid executing the contents of $var:
$ eval echo hi `escape "$var"`
hi ; echo gotcha!
$
A less contrived example is passing arguments to Mail Avenger bodytest commands containing possibly unsafe environment variables. For
example, you might write a hypothetical reject_bcc script to reject mail not explicitly addressed to the recipient:
#!/bin/sh
formail -x to -x cc -x resent-to -x resent-cc
| fgrep "$1" > /dev/null
&& exit 0
echo "<$1>.. address does not accept blind carbon copies"
exit 100
To invoke this script, passing it the recipient address as an argument, you would need to put the following in your Mail Avenger rcpt
script:
bodytest reject_bcc `escape "$RECIPIENT"`
SEE ALSO
avenger(1),
The Mail Avenger home page: <http://www.mailavenger.org/>.
BUGS
escape is designed for the Bourne shell, which is what Mail Avenger scripts use. escape might or might not work with other shells.
AUTHOR
David Mazieres
Mail Avenger 0.8.3 2012-04-05 escape(1)