parameter-substitution.html

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 29&nbsp;exit 0</PRE
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CLASS="VARIABLELIST"
><P
><B
><A
NAME="EXPREPL1"
></A
>变量扩展/子串替换</B
></P
><DL
><DT
></DT
><DD
><P
>这些结构都是从<EM
>ksh</EM
>中引入的.</P
></DD
><DT
><KBD
CLASS="USERINPUT"
>${var:pos}</KBD
></DT
><DD
><P
>变量<TT
CLASS="REPLACEABLE"
><I
>var</I
></TT
>从位置<TT
CLASS="REPLACEABLE"
><I
>pos</I
></TT
>开始扩展(译者注: 也就是pos之前的字符都丢弃).
		  </P
></DD
><DT
><KBD
CLASS="USERINPUT"
>${var:pos:len}</KBD
></DT
><DD
><P
>变量<TT
CLASS="REPLACEABLE"
><I
>var</I
></TT
>从位置<TT
CLASS="REPLACEABLE"
><I
>pos</I
></TT
>开始, 
				并扩展<TT
CLASS="REPLACEABLE"
><I
>len</I
></TT
>个字符.
		    参考<A
HREF="contributed-scripts.html#PW"
>例子 A-14</A
>, 这个例子展示了这种操作的一个创造性的用法. 
		  </P
></DD
><DT
><KBD
CLASS="USERINPUT"
>${var/Pattern/Replacement}</KBD
></DT
><DD
><P
>使用<TT
CLASS="REPLACEABLE"
><I
>Replacement</I
></TT
>来替换变量<TT
CLASS="REPLACEABLE"
><I
>var</I
></TT
>中第一个匹配<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>的字符串. 
			</P
><P
>如果省略<TT
CLASS="REPLACEABLE"
><I
>Replacement</I
></TT
>, 
				那么第一个匹配<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>的字符串将被替换为<EM
>空</EM
>, 也就是被删除了.</P
></DD
><DT
><KBD
CLASS="USERINPUT"
>${var//Pattern/Replacement}</KBD
></DT
><DD
><DIV
CLASS="FORMALPARA"
><P
><B
>全局替换. </B
>所有在变量<TT
CLASS="REPLACEABLE"
><I
>var</I
></TT
>匹配<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>的字符串,
		    都会被替换为<TT
CLASS="REPLACEABLE"
><I
>Replacement</I
></TT
>. </P
></DIV
><P
>和上边一样, 如果省略<TT
CLASS="REPLACEABLE"
><I
>Replacement</I
></TT
>, 
				那么所有匹配<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>的字符串, 
			   都将被替换为<EM
>空</EM
>, 也就是被删除掉. </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="EX7"
></A
><P
><B
>例子 9-20. 使用模式匹配来解析任意字符串</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;
  3&nbsp;var1=abcd-1234-defg
  4&nbsp;echo "var1 = $var1"
  5&nbsp;
  6&nbsp;t=${var1#*-*}
  7&nbsp;echo "var1 (with everything, up to and including first - stripped out) = $t"
  8&nbsp;#  t=${var1#*-}  也一样,
  9&nbsp;#+ 因为#匹配最短的字符串,
 10&nbsp;#+ 同时*匹配任意前缀, 包括空字符串. 
 11&nbsp;# (感谢, Stephane Chazelas, 指出这点.)
 12&nbsp;
 13&nbsp;t=${var1##*-*}
 14&nbsp;echo "If var1 contains a \"-\", returns empty string...   var1 = $t"
 15&nbsp;
 16&nbsp;
 17&nbsp;t=${var1%*-*}
 18&nbsp;echo "var1 (with everything from the last - on stripped out) = $t"
 19&nbsp;
 20&nbsp;echo
 21&nbsp;
 22&nbsp;# -------------------------------------------
 23&nbsp;path_name=/home/bozo/ideas/thoughts.for.today
 24&nbsp;# -------------------------------------------
 25&nbsp;echo "path_name = $path_name"
 26&nbsp;t=${path_name##/*/}
 27&nbsp;echo "path_name, stripped of prefixes = $t"
 28&nbsp;# 在这个特例中, 与	t=`basename $path_name`		效果相同. 
 29&nbsp;#  t=${path_name%/}; t=${t##*/}   是更一般的解决方法.
 30&nbsp;#+ 但有时还是会失败.
 31&nbsp;#  如果$path_name以一个换行符结尾的话, 那么	`basename $path_name` 就不能正常工作了,
 32&nbsp;#+ 但是上边的表达式可以.
 33&nbsp;# (感谢, S.C.)
 34&nbsp;
 35&nbsp;t=${path_name%/*.*}
 36&nbsp;# 与	t=`dirname $path_name`	效果相同.
 37&nbsp;echo "path_name, stripped of suffixes = $t"
 38&nbsp;# 在某些情况下将失效, 比如 "../", "/foo////", # "foo/", "/".
 39&nbsp;#  删除后缀, 尤其是在basename没有后缀的情况下,
 40&nbsp;#+ 但是dirname可以, 不过这同时也使问题复杂化了.
 41&nbsp;# (感谢, S.C.)
 42&nbsp;
 43&nbsp;echo
 44&nbsp;
 45&nbsp;t=${path_name:11}
 46&nbsp;echo "$path_name, with first 11 chars stripped off = $t"
 47&nbsp;t=${path_name:11:5}
 48&nbsp;echo "$path_name, with first 11 chars stripped off, length 5 = $t"
 49&nbsp;
 50&nbsp;echo
 51&nbsp;
 52&nbsp;t=${path_name/bozo/clown}
 53&nbsp;echo "$path_name with \"bozo\" replaced  by \"clown\" = $t"
 54&nbsp;t=${path_name/today/}
 55&nbsp;echo "$path_name with \"today\" deleted = $t"
 56&nbsp;t=${path_name//o/O}
 57&nbsp;echo "$path_name with all o's capitalized = $t"
 58&nbsp;t=${path_name//o/}
 59&nbsp;echo "$path_name with all o's deleted = $t"
 60&nbsp;
 61&nbsp;exit 0</PRE
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><HR></DIV
></DD
><DT
><KBD
CLASS="USERINPUT"
>${var/#Pattern/Replacement}</KBD
></DT
><DD
><P
>如果变量<TT
CLASS="REPLACEABLE"
><I
>var</I
></TT
>的<EM
>前缀</EM
>匹配<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>, 
				那么就使用<TT
CLASS="REPLACEABLE"
><I
>Replacement</I
></TT
>来替换匹配到<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>的字符串.</P
></DD
><DT
><KBD
CLASS="USERINPUT"
>${var/%Pattern/Replacement}</KBD
></DT
><DD
><P
>如果变量<TT
CLASS="REPLACEABLE"
><I
>var</I
></TT
>的<EM
>后缀</EM
>匹配<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>, 
			那么就使用<TT
CLASS="REPLACEABLE"
><I
>Replacement</I
></TT
>来替换匹配到<TT
CLASS="REPLACEABLE"
><I
>Pattern</I
></TT
>的字符串.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="VARMATCH"
></A
><P
><B
>例子 9-21. 对字符串的前缀和后缀使用匹配模式</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# var-match.sh:
  3&nbsp;# 对字符串的前缀和后缀进行模式替换的一个演示.
  4&nbsp;
  5&nbsp;v0=abc1234zip1234abc    # 变量原始值.
  6&nbsp;echo "v0 = $v0"         # abc1234zip1234abc
  7&nbsp;echo
  8&nbsp;
  9&nbsp;# 匹配字符串的前缀(开头).
 10&nbsp;v1=${v0/#abc/ABCDEF}    # abc1234zip1234abc
 11&nbsp;                        # |-|
 12&nbsp;echo "v1 = $v1"         # ABCDEF1234zip1234abc
 13&nbsp;                        # |----|
 14&nbsp;
 15&nbsp;# 匹配字符串的后缀(结尾).
 16&nbsp;v2=${v0/%abc/ABCDEF}    # abc1234zip123abc
 17&nbsp;                        #              |-|
 18&nbsp;echo "v2 = $v2"         # abc1234zip1234ABCDEF
 19&nbsp;                        #               |----|
 20&nbsp;
 21&nbsp;echo
 22&nbsp;
 23&nbsp;#  ----------------------------------------------------
 24&nbsp;#  必须匹配字符串的开头或结尾,
 25&nbsp;#+ 否则是不会产生替换结果的.
 26&nbsp;#  ----------------------------------------------------
 27&nbsp;v3=${v0/#123/000}       # 匹配, 但不是在开头.
 28&nbsp;echo "v3 = $v3"         # abc1234zip1234abc
 29&nbsp;                        # 不会发生替换.
 30&nbsp;v4=${v0/%123/000}       # 匹配, 但不是在结尾.
 31&nbsp;echo "v4 = $v4"         # abc1234zip1234abc
 32&nbsp;                        # 不会发生替换. 
 33&nbsp;
 34&nbsp;exit 0			</PRE
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><HR></DIV
></DD
><DT
><KBD
CLASS="USERINPUT"
>${!varprefix*}</KBD
>, <KBD
CLASS="USERINPUT"
>${!varprefix@}</KBD
></DT
><DD
><P
>匹配所有之前声明过的, 并且以<EM
>varprefix</EM
>开头的变量.
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BORDER="0"
BGCOLOR="#E0E0E0"
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><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;xyz23=whatever
  2&nbsp;xyz24=
  3&nbsp;
  4&nbsp;a=${!xyz*}      # 展开所有以"xyz"开头的, 并且之前声明过的变量名.
  5&nbsp;echo "a = $a"   # a = xyz23 xyz24
  6&nbsp;a=${!xyz@}      # 同上.
  7&nbsp;echo "a = $a"   # a = xyz23 xyz24
  8&nbsp;
  9&nbsp;# Bash, 版本2.04, 添加了这个功能.</PRE
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>
                  </P
></DD
></DL
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>注意事项</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN4933"
HREF="parameter-substitution.html#AEN4933"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>如果在一个非交互脚本中, $parameter被设置为null的话, 
					那么这个脚本将会返回<A
HREF="exitcodes.html#EXITCODESREF"
><SPAN
CLASS="RETURNVALUE"
>127</SPAN
>作为退出状态码</A
>(127返回码对应的Bash错误码为命令未发现<SPAN
CLASS="QUOTE"
>"command not found"</SPAN
>).</P
></TD
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>指定变量的类型: 使用<B
CLASS="COMMAND"
>declare</B
>或者<B
CLASS="COMMAND"
>typeset</B
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