update files and preserve date

UNIX for Advanced & Expert Users
1

I have a bunch of historical files that need to be modified, as the file source announced there is an error in them which should be corrected.

I am planning to use sed to do the mass update, but I would like to know if there is a way to preserve files last modified date/time, so later ls -ltr lists will show me when files were obtained, not when I updated them.

Any idea?

2

cp --preserve=timestamps

3

One way:

filetime()
{
perl -e '      
      $mtime = (stat("$ARGV[0]"))[9];

      # time structure into variables

      ($sec,$min,$hr,$day,$mon,$yr,$wday,@dntcare) = localtime($mtime);
      $yr = ($yr>=70) ? $yr+1900 : $yr+2000;

      printf ("%d%02d%02d%02d%02d", $yr,$mon,$day,$hr,$min); ' "$1"
}
for fname in *.dat
do
# get file time in YYYYMMddhhmm format
   oldtime=$(filetime $fname)
   ls -l $fname
# sed your file here
#  sed 's/  / /g' $fname > tmp; mv tmp $fname
# put filetime back to where it was
  touch -t $oldtime $fname
  ls -l $fname
done
4

Purfect, thanks a million!