01-18-2009
Special symbols in shell scripting
I am new to unix shell scripting, i was going through the existing shell scripts but couldn't able to get enough information on below syntaxes,i mean the symbols $# & $? used in the if loop. what exactly are they? what is the inline meaning, Could you please throw some light.
Examples:
1)
if [ $# -eq 3 ]
then
numFiles=`cat $3 | wc -l | sed 's/ //g'`
#echo $numFiles
count=0
2) if [ $? -eq 0 ]
then
echo "File $line moved to archive on `date +%D`">>$logFile
#echo $'\n' >>$logFile
else
echo "File $line can not be deleted">>$logFile
fi
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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)