In shell script how can we compare (integer and floating point) ,(flaoting point and floating point),(floating point and integer),(integer and integer) with only one if condition.
i have few examples like
set X=3.1
set Y=4.1
if [ $X < $Y ] then
echo "wassup"
endif
But running the above from cron job doesnt seem to work.
The way to carry out floating point operations in bash is to use bc which is available on almost all linux distributions.
# bc will return 0 for false and 1 for true
if [ $(echo "23.3 > 7.3" | bc) -ne 0 ]
then
echo "wassup"
fi
There's a good article available on linux journal about floating point math in bash using bc.
$(echo "$a > $b" | bc) did not return a value. Can you try the subshell on its own?echo $X will be an empty line, for example.Bah itself only handles integers. Use bc:
echo "$X>$Y" | bc
0
echo "$X<$Y" | bc
1
You don't need to worry about scale. It is just for the preocision of output formats:
X=3.000001
Y=3.0001
echo "$X>$Y" | bc
0
echo "$X<$Y" | bc
1
echo "scale=1;$X<$Y" | bc
1
below example works on bash shell.
X=3.1
Y=4.1
if [ $X -le $Y ]
then
echo "wassup"
fi
you may want to learn shell script here
$ test "34.4" -gt "5.4" -> bash: test: 34.4: integer expression expectedbash --version gives me GNU bash, version 4.2.8(1)-release (x86_64-pc-linux-gnu)EDIT. based on the comments to this answer (thanks to user unknown and glenn jackman), it seems that when using bc for a true/false test, the required bash test is simply:
(( $(echo "$X < $Y" |bc) )) ... see the test results and script below wheras, the comparison to -ne 0 is needed for the old style bash [ ] test.
bash does not natively handle floating point numbers, but you can call a utility such as bc
From man bc - An arbitrary precision calculator language
X=3.1
Y=4.1
# This test has two superfluous components.
# See EDIT (above) and TESTS below
if (($(echo "scale=9; $X < $Y" |bc)!=0)) ;then
echo "wassup"
fi
TEST results:
if [ "1" ] true
[ "1" ] true
if [ "0" ] true
[ "0" ] true
if [ 1 ] true
[ 1 ] true
if [ 0 ] true
[ 0 ] true
if (( "1" )) true
(( "1" )) true
if (( "0" )) false
(( "0" )) false
if (( 1 )) true
(( 1 )) true
if (( 0 )) false
(( 0 )) false
echo "1<1"|bc true
echo "1<0"|bc true
TEST script:
printf 'if [ "1" ] '; if [ "1" ]; then echo true; else echo false; fi
printf ' [ "1" ] '; [ "1" ] && echo true || echo false
printf 'if [ "0" ] '; if [ "0" ]; then echo true; else echo false; fi
printf ' [ "0" ] '; [ "0" ] && echo true || echo false
echo
printf 'if [ 1 ] '; if [ 1 ]; then echo true; else echo false; fi
printf ' [ 1 ] '; [ 1 ] && echo true || echo false
printf 'if [ 0 ] '; if [ 0 ]; then echo true; else echo false; fi
printf ' [ 0 ] '; [ 0 ] && echo true || echo false
echo
printf 'if (( "1" )) '; if (("1")); then echo true; else echo false; fi
printf ' (( "1" )) '; (("1")) && echo true || echo false
printf 'if (( "0" )) '; if (("0")); then echo true; else echo false; fi
printf ' (( "0" )) '; (("0")) && echo true || echo false
echo
printf 'if (( 1 )) '; if (( 1 )); then echo true; else echo false; fi
printf ' (( 1 )) '; (( 1 )) && echo true || echo false
printf 'if (( 0 )) '; if (( 0 )); then echo true; else echo false; fi
printf ' (( 0 )) '; (( 0 )) && echo true || echo false
echo
printf 'echo "1<1"|bc '; echo "1<1"|bc >/dev/null && echo true || echo false
printf 'echo "1<0"|bc '; echo "1<0"|bc >/dev/null && echo true || echo false
scale is superfluous, if you just want to test for true and false. !=0 is superfluous too - that's what's done already.
!=0 is not superfluous: bc prints 0 or 1 for false or true. In both cases, the exit status is zero. So, you must compare the command output to something.if (($(echo "$X > $Y" | bc))) ; then echo wassup; else echo pussaw; fi. Reason: $(...) captures the output. ((...)) evaluates.