regex - Using sed and grep/egrep to search and replace

Question

I am using egrep -R followed by a regular expression containing about 10 unions, so like: .jpg | .png | .gif etc. This works well, now I would like to replace all strings found with .bmp

I was thinking of something like

egrep -lR ".jpg|.png|.gif" . | sed "s/some_expression/.jpg/" file_it_came_form

so the issue here is how do I do a similar union regular expression in sed and how do I tell it to save the changes to the file that it got the input from.

Answer 1

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 as record separator

  • ".jpg|.png|.gif": match one of the strings ".jpg", ".gif" or ".png"

  • .: start the search in the current directory

• xargs: execute a command with the stdin as argument

  • -0: use 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 parameter

• sed: 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"