在我浏览一些现有脚本时,我是Shell脚本的新手。我了解以下命令
db2 -x some command | read
param
param=${param## };
param=${param%% };
任何人都可以通过它来理解
答案 0 :(得分:0)
在bash手册页中:
${parameter##word}
Remove matching prefix pattern. The word is expanded to produce
a pattern just as in pathname expansion. If the pattern matches
the beginning of the value of parameter, then the result of the
expansion is the expanded value of parameter with the shortest
matching pattern (the ``#'' case) or the longest matching patâ
tern (the ``##'' case) deleted. If parameter is @ or *, the
pattern removal operation is applied to each positional parameâ
ter in turn, and the expansion is the resultant list. If paramâ
eter is an array variable subscripted with @ or *, the pattern
removal operation is applied to each member of the array in
turn, and the expansion is the resultant list.
${parameter%%word}
Remove matching suffix pattern. The word is expanded to produce
a pattern just as in pathname expansion. If the pattern matches
a trailing portion of the expanded value of parameter, then the
result of the expansion is the expanded value of parameter with
the shortest matching pattern (the ``%'' case) or the longest
matching pattern (the ``%%'' case) deleted. If parameter is @
or *, the pattern removal operation is applied to each posiâ
tional parameter in turn, and the expansion is the resultant
list. If parameter is an array variable subscripted with @ or
*, the pattern removal operation is applied to each member of
the array in turn, and the expansion is the resultant list.
因此,总而言之,请牢记您的示例,param = $ {param ##};将删除变量param中的前导空格,而$ {parameter %% word}将删除尾部空格