在Bash中提取子字符串

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给定文件名格式someletters_12345_moreleters.ext ，我想提取5位数字并将其放入变量中。

因此，为了强调这一点，我有一个文件名，其中包含x个字符，然后是一个五位数的序列，在两侧用单个下划线包围，然后是另一组x个字符。我想使用5位数字并将其放入变量中。

我对实现此目标的许多不同方式非常感兴趣。

#1楼

如果有人需要更严格的信息，您也可以像这样在man bash中搜索它

$ man bash [press return key]
/substring  [press return key]
[press "n" key]
[press "n" key]
[press "n" key]
[press "n" key]

结果：

${parameter:offset}
       ${parameter:offset:length}
              Substring Expansion.  Expands to  up  to  length  characters  of
              parameter  starting  at  the  character specified by offset.  If
              length is omitted, expands to the substring of parameter  start‐
              ing at the character specified by offset.  length and offset are
              arithmetic expressions (see ARITHMETIC  EVALUATION  below).   If
              offset  evaluates  to a number less than zero, the value is used
              as an offset from the end of the value of parameter.  Arithmetic
              expressions  starting  with  a - must be separated by whitespace
              from the preceding : to be distinguished from  the  Use  Default
              Values  expansion.   If  length  evaluates to a number less than
              zero, and parameter is not @ and not an indexed  or  associative
              array,  it is interpreted as an offset from the end of the value
              of parameter rather than a number of characters, and the  expan‐
              sion is the characters between the two offsets.  If parameter is
              @, the result is length positional parameters beginning at  off‐
              set.   If parameter is an indexed array name subscripted by @ or
              *, the result is the length members of the array beginning  with
              ${parameter[offset]}.   A  negative  offset is taken relative to
              one greater than the maximum index of the specified array.  Sub‐
              string  expansion applied to an associative array produces unde‐
              fined results.  Note that a negative offset  must  be  separated
              from  the  colon  by  at least one space to avoid being confused
              with the :- expansion.  Substring indexing is zero-based  unless
              the  positional  parameters are used, in which case the indexing
              starts at 1 by default.  If offset  is  0,  and  the  positional
              parameters are used, $0 is prefixed to the list.

#2楼

我很惊讶这种纯bash解决方案没有出现：

a="someletters_12345_moreleters.ext"
IFS="_"
set $a
echo $2
# prints 12345

您可能希望将IFS重置为之前的值，或者之后将其unset IFS ！

#3楼

类似于PHP中的substr（'abcdefg'，2-1，3）：

echo 'abcdefg'|tail -c +2|head -c 3

#4楼

遵循要求

我有一个带有x个字符的文件名，然后是一个五位数的序列，在两侧由单个下划线包围，然后是另一组x个字符。我想使用5位数字并将其放入变量中。

我发现了一些可能有用的grep方法：

$ echo "someletters_12345_moreleters.ext" | grep -Eo "[[:digit:]]+" 
12345

或更好

$ echo "someletters_12345_moreleters.ext" | grep -Eo "[[:digit:]]{5}" 
12345

然后使用-Po语法：

$ echo "someletters_12345_moreleters.ext" | grep -Po '(?<=_)\d+' 
12345

或者，如果您想使其恰好适合5个字符，请执行以下操作：

$ echo "someletters_12345_moreleters.ext" | grep -Po '(?<=_)\d{5}' 
12345

最后，要将其存储在变量中，只需使用var=$(command)语法。

#5楼

有点晚了，但我遇到了这个问题，发现了以下内容：

host:/tmp$ asd=someletters_12345_moreleters.ext 
host:/tmp$ echo `expr $asd : '.*_\(.*\)_'`
12345
host:/tmp$

我用它来获得日期为％N的嵌入式系统的毫秒级分辨率：

set `grep "now at" /proc/timer_list`
nano=$3
fraction=`expr $nano : '.*\(...\)......'`
$debug nano is $nano, fraction is $fraction

来源：oschina

链接：https://my.oschina.net/stackoom/blog/3146814

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bash

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