Inklusive end，类似于JS和Java实现。删除+1如果你不想这样做。

function substring() {
    local str="$1" start="${2}" end="${3}"
    
    if [[ "$start" == "" ]]; then start="0"; fi
    if [[ "$end"   == "" ]]; then end="${#str}"; fi
    
    local length="((${end}-${start}+1))"
    
    echo "${str:${start}:${length}}"
} 

例子:

    substring 01234 0
    01234
    substring 012345 0
    012345
    substring 012345 0 0
    0
    substring 012345 1 1
    1
    substring 012345 1 2
    12
    substring 012345 0 1
    01
    substring 012345 0 2
    012
    substring 012345 0 3
    0123
    substring 012345 0 4
    01234
    substring 012345 0 5
    012345

更多示例调用:

    substring 012345 0
    012345
    substring 012345 1
    12345
    substring 012345 2
    2345
    substring 012345 3
    345
    substring 012345 4
    45
    substring 012345 5
    5
    substring 012345 6
    
    substring 012345 3 5
    345
    substring 012345 3 4
    34
    substring 012345 2 4
    234
    substring 012345 1 3
    123

没有任何子过程，您可以:

shopt -s extglob
front=${input%%_+([a-zA-Z]).*}
digits=${front##+([a-zA-Z])_}

一个非常小的变体也可以在ksh93中工作。

减少使用:

echo 'someletters_12345_moreleters.ext' | cut -d'_' -f 2

更通用的:

INPUT='someletters_12345_moreleters.ext'
SUBSTRING=$(echo $INPUT| cut -d'_' -f 2)
echo $SUBSTRING

这是一个substring.sh文件

使用

`substring.sh $TEXT 2 3` # characters 2-3

`substring.sh $TEXT 2` # characters 2 and after 

Substring.sh遵循这一行

#echo "starting substring"
chars=$1
start=$(($2))
end=$3

i=0
o=""
if [[ -z $end ]]; then
  end=`echo "$chars " | wc -c`
else
  end=$((end))
fi
#echo "length is " $e
a=`echo $chars | sed  's/\(.\)/\1 /g'`
#echo "a is " $a
for c in $a
do
  #echo "substring" $i $e $c
  if [[ i -lt $start ]]; then
    : # DO Nothing
  elif [[ i -gt $end ]]; then
    break;
  else
    o="$o$c"
  fi
  i=$(($i+1))
done
#echo substring returning $o
echo $o

如果有人想要更严格的信息，你也可以像这样在man bash中搜索

$ 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.

类似于php中的substr('abcdefg'， 2-1, 3):

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