请教个脚本问题

yunxia

if [ -n "$1" -a "$1" != "${1//[^0-9]/}” ];then

==》${1//[^0-9]/}这句怎么理解啊 $1为脚本第一个参数。

biinn

判断$1是以数字开头？
-----------------
更改：^理解错误。正确的是判断$1包含字母

FreeOrDie

${1//[^0-9]/}是模式替换。格式是${parameter/pattern/string}。这里的parameter是1，pattern是"/^[0-9]"，string被省略了，我觉得解释为空。pattern以斜杠开头是说在$parameter中所有的匹配都替换为string。所以${1//[^0-9]/}就是将位置变量$1中所有的非数字([^0-9])替换为空。
参见man bash 中 EXPANSION小节。

${parameter/pattern/string}
              Pattern substitution.  The pattern is expanded to produce a pattern just as in pathname expansion.
              Parameter is expanded and the longest match of pattern against its value is replaced with  string.
              If  pattern  begins  with  /,  all matches of pattern are replaced with string.  Normally only the
              first match is replaced.  If pattern begins with #, it must match at the beginning of the expanded
              value  of  parameter.  If pattern begins with %, it must match at the end of the expanded value of
              parameter.  If string is null, matches of pattern are deleted and the / following pattern  may  be
              omitted.  If parameter is @ or *, the substitution operation is applied to each positional parame‐
              ter in turn, and the expansion is the resultant list.  If parameter  is  an  array  variable  sub‐
              scripted  with  @ or *, the substitution operation is applied to each member of the array in turn,
              and the expansion is the resultant list.