在Shell中获取当前全路径

Zookeeper.sh中的样本：
ZOOBIN="${BASH_SOURCE-$0}"
ZOOBIN=`dirname ${ZOOBIN}`
ZOOBINDIR=`cd ${ZOOBIN}; pwd`

注意这里"${BASH_SOURCE-$0}"的用法


下面内容来自：
http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_02

${parameter:-word}Use Default Values. If parameter is unset or null, the expansion of word shall be substituted; otherwise, the value of parameter shall be substituted.

${parameter:=word}Assign Default Values. If parameter is unset or null, the expansion of word shall be assigned to parameter. In all cases, the final value of parameter shall be substituted. Only variables, not positional parameters or special parameters, can be assigned in this way.

${parameter:?[word]}Indicate Error if Null or Unset. If parameter is unset or null, the expansion of word (or a message indicating it is unset if word is omitted) shall be written to standard error and the shell exits with a non-zero exit status. Otherwise, the value of parameter shall be substituted. An interactive shell need not exit.

${parameter:+word}Use Alternative Value. If parameter is unset or null, null shall be substituted; otherwise, the expansion of word shall be substituted.

In the parameter expansions shown previously, use of the colon in the format shall result in a test for a parameter that is unset or null; omission of the colon shall result in a test for a parameter that is only unset. The following table summarizes the effect of the colon:

	parameter	parameter	parameter
	Set and Not Null	Set But Null	Unset
${parameter:-word}	substitute parameter	substitute word	substitute word
${parameter-word}	substitute parameter	substitute null	substitute word
${parameter:=word}	substitute parameter	assign word	assign word
${parameter=word}	substitute parameter	substitute null	assign word
${parameter:?word}	substitute parameter	error, exit	error, exit
${parameter?word}	substitute parameter	substitute null	error, exit
${parameter:+word}	substitute word	substitute null	substitute null
${parameter+word}	substitute word	substitute word	substitute null

In all cases shown with "substitute", the expression is replaced with the value shown. In all cases shown with "assign", parameter is assigned that value, which also replaces the expression.

${#parameter}String Length. The length in characters of the value of parameter shall be substituted. If parameter is '*' or '@', the result of the expansion is unspecified.

The following four varieties of parameter expansion provide for substring processing. In each case, pattern matching notation (see Pattern Matching Notation), rather than regular expression notation, shall be used to evaluate the patterns. If parameter is '*' or '@', the result of the expansion is unspecified. Enclosing the full parameter expansion string in double-quotes shall not cause the following four varieties of pattern characters to be quoted, whereas quoting characters within the braces shall have this effect.

${parameter%word}Remove Smallest Suffix Pattern. The word shall be expanded to produce a pattern. The parameter expansion shall then result in parameter, with the smallest portion of the suffix matched by the pattern deleted.

${parameter%%word}Remove Largest Suffix Pattern. The word shall be expanded to produce a pattern. The parameter expansion shall then result in parameter, with the largest portion of the suffix matched by the pattern deleted.

${parameter#word}Remove Smallest Prefix Pattern. The word shall be expanded to produce a pattern. The parameter expansion shall then result in parameter, with the smallest portion of the prefix matched by the pattern deleted.

${parameter##word}Remove Largest Prefix Pattern. The word shall be expanded to produce a pattern. The parameter expansion shall then result in parameter, with the largest portion of the prefix matched by the pattern deleted.