Use this command:
egrep -lRZ "\.jpg|\.png|\.gif" . \
| xargs -0 -l sed -i -e 's/\.jpg\|\.gif\|\.png/.bmp/g'
egrep: find matching lines using extended regular expressions-l: only list matching filenames-R: search recursively through all given directories-Z: use \0 as record separator"\.jpg|\.png|\.gif": match one of the strings ".jpg", ".gif" or ".png".: start the search in the current directoryxargs: execute a command with the stdin as argument-0: use \0 as record separator. This is important to match the -Z of egrep and to avoid being fooled by spaces and newlines in input filenames.-l: use one line per command as parametersed: the stream editor-i: replace the input file with the output without making a backup-e: use the following argument as expression's/\.jpg\|\.gif\|\.png/.bmp/g': replace all occurrences of the strings ".jpg", ".gif" or ".png" with ".bmp"
