Question

I have a text file with lines saying:

File fileA and fileB differ 
File fileX and fileY differ

I need a bash script that goes through the whole file, for each line parses the file names and executes the command diff fileA fileB > fileA.diff

Answer 1

The following command:

awk '/ differ$/ {print "diff "$2" "$4" >"$2".diff"}{}'

will give you a script you can run to do this.

See the following transcript:

pax$ echo 'File fileA and fileB differ
hello
File fileX and fileY differ' | awk '
    / differ$/ {print "diff "$2" "$4" >"$2".diff"}{}'
diff fileA fileB >fileA.diff
diff fileX fileY >fileX.diff

Capture the output, then run it with bash and you’ll have what you need.

Note that this won’t work well with filenames that have spaces in them – if you have such heinous beasts, you will need to do a little more intelligent parsing.