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why some time $( ) and some time ${ } ??
08-28-2006
why some time $( ) and some time ${ } ??
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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)