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.