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Unix 쉘에서의 산술 비교

Unix 쉘에서의 산술 비교는 정수값에 한정되어 있다. 다음은 기본적인
쉘 명령을 사용하여 부동 소수값을 비교하는 팁이다.

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#! /bin/sh
# test shell script
n1="01.401"
n2="01.350"

function compareFloatSmall
{
sort -n <<: | head -1
$n1
$n2
:
}

function compareFloatGreat
{
sort -r -n <<: | head -1
$n1
$n2
:
}

small=$(compareFloatSmall $n1 $n2)
echo "Comparing $n1 to $n2: smaller $less"
great=$(compareFloatGreat $n1 $n2)
echo "Comparing $n1 to $n2: greater $great"
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다른 방법으로 'awk' 프로그램을 사용할 수 있다.
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#! /bin/sh
# A couple of examples in awk.
n1="03.550"
n2="02.550"

echo "$n1 $n2" | awk '{
       if ( $1 >= $2 ) print $1
       if ( $1 <= $2 ) print $2
       if ( $1 >  $2 ) print $1
       if ( $1 <  $2 ) print $2
       if ( $1 == $2 ) print $1, $2
}'
--------- CUT AGAIN HERE-----------

<><><><><><><><><><>원 문<><><><><><><><><><><>
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                             UNIX GURU UNIVERSE
                                UNIX HOT TIP

                       Unix Tip 2926 - February  9, 2009

                   http://www.ugu.com/sui/ugu/show?tip.today

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ARITHMETIC COMPARISON

In UNIX shell arithmetic comparison
is limited to integer values.  Here
is a tip to compare floating values
using basic shell commands.

--------- CUT HERE-----------------

#! /bin/sh
# test shell script
n1="01.401"
n2="01.350"

function compareFloatSmall
{
sort -n <<: | head -1
$n1
$n2
:
}

function compareFloatGreat
{
sort -r -n <<: | head -1
$n1
$n2
:
}

small=$(compareFloatSmall $n1 $n2)
echo "Comparing $n1 to $n2: smaller $less"
great=$(compareFloatGreat $n1 $n2)
echo "Comparing $n1 to $n2: greater $great"

--------- CUT HERE-----------------

Alternatively you can use a small 'awk' program.

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#! /bin/sh
# A couple of examples in awk.
n1="03.550"
n2="02.550"

echo "$n1 $n2" | awk '{
       if ( $1 >= $2 ) print $1
       if ( $1 <= $2 ) print $2
       if ( $1 >  $2 ) print $1
       if ( $1 <  $2 ) print $2
       if ( $1 == $2 ) print $1, $2
}'
--------- CUT AGAIN HERE-----------

                    # > /var/log/messages


참고 원문
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                             UNIX GURU UNIVERSE
                                UNIX HOT TIP

                       Unix Tip 3151 - September 21, 2008

                   http://www.ugu.com/sui/ugu/show?tip.today

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NULL IT FAST

Here is the fastest way to truncate a file to zero
bytes in a bourne or korn shell.

$ > /var/log/messages

This is a good method, if the file has to be truncated,
but is opened by another process. For example, if you
want to truncate /var/log/messages, which is held
open by syslogd...