Question

I need to copy .csv files from one directory to another, and while doing so need to reformat the first column, which is a date column, from 13/04/2012 to 2012-04-13. What is the sed syntax to perform this simple conversion? I am getting awfully confused by the sed stuff I’m reading on the web.

Answer 1

What have you tried so far? You could start with something small like this as a test case:

echo "13/04/2012;Col2;Col3" | sed -E 's#^([^/]+)/([^/]+)/([0-9]+)(.*)#\3-\2-\1\4#'

s           = substitution command
#           = start of pattern
^           = start of line
([^/]+)/    = group of all non-/-characters followed by a / (day)
([^/]+)/    = group of all non-/-characters followed by a / (month)
([0-9]+)    = group of at least one digit (year)
(.*)        = rest of line
#           = start of replacement
\3          = backward reference to capture of third group (year)
\2          = backward reference to capture of second group (month)
\1          = backward reference to capture of first group (day)
\4          = backward reference to capture of fourth group (rest of line)
# end of command