How to read date from terminal and compare with current date

Question

I want to know the appropriate way of reading date from terminal and comparing with current date using shell script,

I have the below script,

a=`date +%Y-%m-%d`
while [ 1 ] ; do
        echo "Enter Date"
    read todate
    if [ $todate < $a ];then
        break;
    fi
    echo "todate greater than curDate" 
done

it is not running as expected. Please help me.

UPDATE

Here is my final version,

#! /bin/bash
DATE=$(date '+%s')
while [ 1 ] ; do
        echo "Enter Date[DD MM YYYY]:"    
    read D M Y
    THIS=$(date -d "$Y-$M-$D" '+%s')

    if (( THIS < DATE )) ; then
        break
    fi
done

Thanks everyone!

use the **date** command as explained here: http://stackoverflow.com/a/5895607/828193 — user000001, Jan 24 '13 at 12:53
`[ $todate < $a ]'` invokes the command `[` with the arguments `$todate ]` and input redirected from the file named in the variable `a`. I suspect that is not what you intend. Use `[ $a -lt $b ]` to compare integers. — William Pursell, Jan 24 '13 at 13:07

score 4 · Answer 1 · answered Jan 24 '13 at 13:09

4

from Advanced Bash-Scripting Guide:

7.3. Other Comparison Operators

...

string comparison

...

<
    is less than, in ASCII alphabetical order

    if [[ "$a" < "$b" ]]

    if [ "$a" \< "$b" ]

    Note that the "<" needs to be escaped within a [ ] construct.

So, your

   if [ $todate < $a ];then

becomes

if [ $todate \< $a ];then

or

if [[ $todate < $a ]];then

answered Jan 24 '13 at 13:09

Alexey Shumkin

409
3
8

Since not every `date` supports `%s` this is slightly more portable, with the caveat that you must always use YMD order and zero padding (i.e. `+%Y-%m-%d` as in the original questions). – mr.spuratic Jan 24 '13 at 13:29
Note that not all versions of `[` (nor all shells for which `[` is a builtin) will accept `<` as an operator. `bash`, and surprisingly `dash` accept `<`. `ksh` and `zsh` do not. – William Pursell Jan 24 '13 at 18:12

score 2 · Answer 2 · answered Jan 24 '13 at 12:59

2

date has +%s format.

 %s     seconds since 1970-01-01 00:00:00 UTC

you save current date in second. Then convert user input date also in second. so you could compare.

answered Jan 24 '13 at 12:59

Kent

189,393
32
233
301

score 0 · Answer 3 · answered Jan 24 '13 at 13:55

Here is the solution:

Here in this solution i am converting dates to single integer and it is obvious that greater date will always be larger integer than current date

a=date +%Y%m%d

while [ 1 ] ; do

echo "Enter Date" read todate echo "$todate" > temp

for i in 1 2 3
    do 
      y=`cut -d- -f$i temp`
      x=$x$y
    done 
if [ $x -lt $a ];then
    exit;
fi
echo "todate greater than curDate"

done

How to read date from terminal and compare with current date

3 Answers3

Here is the solution:

Here in this solution i am converting dates to single integer and it is obvious that greater date will always be larger integer than current date

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