In a unix shell how to get yesterday s date into a variable

Question

I ve got a shell script which does the following to store the current day s date in a variable  dt    date    a  d  m  Y    read dt echo   dt    How would i go about getting yesterdays date into a variable   Basically what i m trying to achieve is to use grep to pull all of yesterday s lines from a log file  since each line in the log contains the date in  Mon 01 02 2010  format   Thanks a lot

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If you have access to python  this is a helper that will get the yyyy-mm-dd date value for any arbitrary n days ago   function get n days ago     local days  1   python -c  import datetime  print  datetime date today   - datetime timedelta   days    isoformat         today is 2014-08-24    get n days ago 1 2014-08-23    get n days ago 2 2014-08-22

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ksh93   dt    printf     a  d  m  Y T  yesterday      or   dt   printf     a  d  m  Y T  yesterday    The first one runs in the same process  the second one in a subshell

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Here is a ksh script to calculate the previous date of the first argument  tested on Solaris 10      bin ksh  sep     today   date    Y m d    today   1 -today   ty  echo  today cut -b1-4    today year  tm  echo  today cut -b5-6    today month  td  echo  today cut -b7-8    today day  yy 0   yesterday year  ym 0   yesterday month  yd 0   yesterday day   if   td -gt 1     then            today is not first of month          let yy ty         same year          let ym tm         same month          let yd td-1       previous day  else            today is first of month          if   tm -gt 1             then                    today is not first of year                  let yy ty         same year                  let ym tm-1       previous month                  if   ym -eq 1 -o ym -eq 3 -o ym -eq 5 -o ym -eq 7 -o ym -eq 8 -o ym -     eq 10 -o ym -eq 12                     then                          let yd 31                  fi                  if   ym -eq 4 -o ym -eq 6 -o ym -eq 9 -o ym -eq 11                     then                          let yd 30                  fi                  if   ym -eq 2                     then                            shit                                if   ty 4 -eq 0                             then                                  if   ty 100 -eq 0                                     then                                          if   ty 400 -eq 0                                             then                                           echo divisible by 4  by 100  by 400                                                  leap 1                                           else                                           echo divisible by 4  by 100  not by 400                                                  leap 0                                          fi                                  else                                           echo divisible by 4  not by 100                                          leap 1                                   fi                          else                                   echo not divisible by 4                                  leap 0   not divisible by four                          fi                          let yd 28 leap                  fi          else                    today is first of year                    yesterday was 31-12-yy                  let yy ty-1       previous year                  let ym 12                  let yd 31          fi  fi  printf   4d  sep  02d  sep  02d n   yy  ym  yd   Tests  bin  for date in 20110902 20110901 20110812 20110801 20110301 20100301 20080301 21000301 20000301 20000101   do yesterday  date  done 20110901 20110831 20110811 20110731 20110228 20100228 20080229 21000228 20000229 19991231

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dt   date --date yesterday    a  d  m  Y   echo  dt

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If your HP-UX installation has Tcl installed  you might find it s date arithmetic very readable  unfortunately the Tcl shell does not have a nice  -e  option like perl    dt   echo  puts  clock format  clock scan yesterday  -format   a  d  m  Y      tclsh  echo  yesterday was  dt    This will handle all the daylight savings bother

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Though all good answers  unfortunately none of them worked for me  So I had to write something old school    I was on a bare minimal Linux OS      date -d     echo       date   s -   60 60 24          You can combine this with date s usual formatting  Eg      date -d     echo       date   s -   60 60 24          Y- m- d   Explanation    Take date input in terms of epoc seconds   the -d option    from which you would have subtracted one day equivalent seconds  This will give the date precisely one day back

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If you have Perl available  and your date doesn t have nice features like yesterday   you can use   pax gt  date Thu Aug 18 19 29 49 XYZ 2010  pax gt  dt   perl -e  use POSIX print strftime   d  m  Y   localtime time-86400     pax gt  echo  dt 17 08 2010

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If you are on a Mac or BSD or something else without the --date option  you can use   date -r  expr   date   s   - 86400     a  d  m  Y    Update  or perhaps     date -r     date   s  - 86400      a  d  m  Y

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I have shell script in Linux and following code worked for me      bin bash yesterday  TZ EST 24 date   Y m d    Yesterday is a variable mkdir  yesterday   creates a directory with  YYYYMMDD format

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On Linux  you can use  date -d  -1 days     a  d  m  Y

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You have atleast 2 options   Use perl   perl -e   T localtime time-86400  printf   02d  02d  02d   T 4  1  T 3   T 5  1900    Install GNU date  it s in the sh utils package if I remember correctly   date --date yesterday    a  d  m  Y    read dt echo   dt   Not sure if this works  but you might be able to use a negative timezone  If you use a timezone that s 24 hours before your current timezone than you can simply use date

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var  TZ  TZ  TZ 24  date  TZ  var    Will get you yesterday in AIX and set back the TZ variable back to original

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Try the following method   dt  case   OSTYPE  in darwin   date -v-1d    s         date -d  1 days ago     s   esac  echo  dt   It works on both Linux and OSX

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Thanks for the help everyone  but since i m on HP-UX  after all  the more you pay  the less features you get     i ve had to resort to perl   perl -e   T localtime time-86400  printf   02d  02d  04d   T 3   T 4  1  T 5  1900     read dt

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For Hp-UX only below command worked for me   TZ aaa24 date   Y m d  you can use it as    ydate  TZ aaa24 date   Y m d   echo  ydate

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If you don t have a version of date that supports --yesterday and you don t want to use perl  you can use this handy ksh script of mine   By default  it returns yesterday s date  but you can feed it a number and it tells you the date that many days in the past  It starts to slow down a bit if you re looking far in the past  100 000 days ago it was 1 30 1738  though my system took 28 seconds to figure that out           bin ksh -p      t  date   j      ago  1     ago   ago  1    in days     y  date   Y       function build year               set -A j X    for m in 01 02 03 04 05 06 07 08 09 10 11 12                                                   cal  m  y   sed -e  1 2d  -e  s       -e  s     0-9      m   1 g                                      yeardays        j     - 1               build year      until    ago -lt  t       do                y y-1                build year                ago   ago - t                t  yeardays     done      print   j     t - ago       y

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You can use GNU date command as shown below     Getting Date In the Past      To get yesterday and earlier day in the past use string day ago    date --date  yesterday   date --date  1 day ago   date --date  10 day ago   date --date  10 week ago   date --date  10 month ago   date --date  10 year ago      Getting Date In the Future      To get tomorrow and day after tomorrow  tomorrow N  use day word to get date in the future as follows    date --date  tomorrow   date --date  1 day   date --date  10 day   date --date  10 week   date --date  10 month   date --date  10 year

[unix] In a unix shell, how to get yesterday's date into a variable?

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