how to compare file modification time in bourne shell script

[Mike Moore]

In article <1990Jul23.233044.2729 at silma.com> aab at silma.UUCP () writes:
>
>I need to compare the modification times of two files in a bourne shell
>script. I would like to do this without writing C code.
>Machine is Sparcstation 1 running SunOS 4.03c
>
>Thus I need a function:
>
>newer file1 file2
>
>that returns 0 if file1 is newer than file2 else returns 1
>
>Can it be done?

Here is a way:

     newer() {
       file=$1
       set `ls -t $1 $2`   # func args are now changed
       [ $file = $1 ] && return 0 || return 1
     }

For those that don't know, the second line is an alternative form of:

     if [ $file = $1 ]
       then
         return 0
       else
         return 1
     fi

Of course, file1 and file2 have to exist, and have to be files.

If you don't want to use set, then:

     [ `ls -tC $1 $2 | sed 's/ .*$//'` = $1 ] && return 0 || return 1

And to do the whole thing properly:

     newer() {
       file=$1
       [ ! -f $1 -o ! -f $2 ] && return 2   # error exit
       set `ls -dt $1 $2`                   # func args are changed
       [ $file = $1 ] && return 0 || return 1
     }

Now file1 and file2 don't have to exist and don't have to be files.
Line #2 in this final version could be changed to two seperate lines:

     [ ! -f $1 ] && return 1  # since file2 is newer
     [ ! -f $2 ] && return 0  # since file1 is newer

if you want a different effect.

Using this method, then, on most machines, the only program actually read from
disk and executed is ls (some may actually execute the '[').

Happy Bourne Shell!

Mike
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