split a string variable through shell script - linux

Question

i have a string containing date and time as timestamp= 12-12-2012 16:45:00
I need to reformat it into timestamp= 16:45:00 12-12-2012
How to achieve this in shell script?
Note Please : variable's value is 12-12-2012 16:45:00 and timestamp is the name of variable
#!usr/bin/expect
set timestamp "16:45:00 12-12-2012"
Now what should i do so value of timestamp will become 12-12-2012 16:45:00
script extention is .tcl example test.tcl

Answer 1

You could use variable patterned removal. ## means "greedily remove everything that matches the pattern, starting from the left". %% means the same from the right:
tm=${timestamp##* }
dt=${timestamp%% *}
result="$tm $dt"
or you could use cut to do the same, giving a field delimiter:
tm=$(echo $timestamp | cut -f2 -d' ')
dt=$(echo $timestamp | cut -f1 -d' ')
result="$tm $dt"
or you could use sed to swap them with a regex (see other post).
or if you are pulling the date from the date command, you could ask it to format it for you:
result=$(date +'%r %F')
and for that matter, you might have a version of date that will parse your date and then let you express it however you want:
result=$(date -d '12/12/2012 4:45 pm' +'%r %F')
admittedely, this last one is picky about date input...see "info date" for information on accepted inputs.
If you want to use regex, I like Perl's...they are cleaner to write:
echo $timestamp | perl -p -e 's/^(\S+)\s+(\S+)/$2 $1/'
where \S matches non-space characters, + means "one or more", and \s matches spaces. The parens do captures of the parts matched.
EDIT:
Sorry, didn't realize that the "timestamp=" was part of the actual data. All of the above example work if you first strip that bit out:
var='timestamp=2012-12-12 16:45:11'
timestamp=${var#timestamp=}
... then as above ...

Answer 2

Using sed:
sed 's/\([0-9]*-[0-9]*-[0-9]*\)\([ \t]*\)\(.*\)/\3\2\1/' input
this command works on lines containing the pattern number-number-number whitespace antyhing. It simply swaps the number-number-number part \([0-9]*-[0-9]*-[0-9]*\) with the anything part \(.*\), also keeping the original whitespaces \([ \t]*\). So the replace part of sed is \3\2\1, which means the third part, white spaces, and the first part.
Same logic with tcl:
set timestamp "12-12-2012 16:45:00"
set s [regsub {([0-9]*-[0-9]*-[0-9]*)([ \t]*)(.*)} $timestamp \\3\\2\\1]
puts $s

Answer 3

awk solution here:
string="timestamp= 12-12-2012 16:45:00"
awk '{print $1, $3, $2}' <<< "$string"

Answer 4

In bash (and similar shells):
$ timestamp="12-12-2012 16:45:00"
$ read -a tsarr <<< "$timestamp"
$ echo "${tsarr[1]} ${tsarr[0]}"
16:45:00 12-12-2012