linux - 这个 bash 文件名提取技术的用途？

Question

我有一部分 bash 脚本正在获取不带扩展名的文件名，但我试图了解这里到底发生了什么。 “%%”是干什么用的？有人可以详细说明 bash 在幕后做什么吗？如何在一般基础上使用这种技术？

#!/bin/bash

for src in *.tif
    do
    txt=${src%%.*}
    tesseract ${src} ${txt}
    done

Answer 1

它去掉了文件扩展名(此处:.tif)，示例:

$ for A in test.py test.sh test.xml test.xsl; do echo "$A: ${A%%.*}"; done
test.py: test
test.sh: test
test.xml: test
test.xsl: test

来自 bash 手册:

   ${parameter%%word}
          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 positional 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.