Uses for this bash filename extraction technique?

Question

I have a portion of a bash script that is getting a filename without extension, but I'm trying to understand what is really going on here. What are the "%%"'s for? Can someone elaborate on what bash is doing behind the scenes? How can this technique be used on a general basis?

#!/bin/bash

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

Answer 1

It gets rid of the filename extension (here: .tif), sample:

$ 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

from bash manual:

   ${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.

Answer 2

Here's output from the bash man page

 ${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 pat-
          tern (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.

Answer 3

Apparently bash has several "Parameter Expansion" tools which include:

Simply substituting the value...

${parameter}

Expanding to a sub-string...

${parameter:offset}
${parameter:offset:length}

Substitute the length of the parameters value...

${#parameter}

Expanding upon a match at the beginning of the parameter...

${parameter#word}
${parameter##word}

Expanding upon a match at the end of the parameter...

${parameter%word}
${parameter%%word}

Expands the parameter to find and replace a string...

${parameter/pattern/string}

These are my interpretation of the parts I think I understand from this section of the man pages. Let me know if I missed something important.