I'm unable to get numeric comparisons working:
echo "enter two numbers";
read a b;
echo "a=$a";
echo "b=$b";
if [ $a \> $b ];
then
echo "a is greater than b";
else
echo "b is greater than a";
fi;
The problem is that it compares the number from the first digit on, i.e. 9 is bigger than 10, but 1 is greater than 09.
How can I convert the numbers into a type to do a true comparison?
There is also one nice thing some people might not know about:
echo $(( a < b ? a : b ))
This code will print the smallest number out of a
and b
If you have floats you can write a function and then use that e.g.
#!/bin/bash
function float_gt() {
perl -e "{if($1>$2){print 1} else {print 0}}"
}
x=3.14
y=5.20
if [ $(float_gt $x $y) == 1 ] ; then
echo "do stuff with x"
else
echo "do stuff with y"
fi
The bracket stuff (e.g., [[ $a -gt $b ]]
or (( $a > $b ))
) isn't enough if you want to use float numbers as well; it would report a syntax error. If you want to compare float numbers or float number to integer, you can use (( $(bc <<< "...") ))
.
For example,
a=2.00
b=1
if (( $(bc <<<"$a > $b") )); then
echo "a is greater than b"
else
echo "a is not greater than b"
fi
You can include more than one comparison in the if statement. For example,
a=2.
b=1
c=1.0000
if (( $(bc <<<"$b == $c && $b < $a") )); then
echo "b is equal to c but less than a"
else
echo "b is either not equal to c and/or not less than a"
fi
That's helpful if you want to check if a numeric variable (integer or not) is within a numeric range.
In Bash I prefer doing this as it addresses itself more as a conditional operation unlike using (( ))
which is more of arithmetic.
[[ N -gt M ]]
Unless I do complex stuffs like
(( (N + 1) > M ))
But everyone just has their own preferences. Sad thing is that some people impose their unofficial standards.
Update:
You actually can also do this:
[[ 'N + 1' -gt M ]]
Which allows you to add something else which you could do with [[ ]]
besides arithmetic stuff.
I solved this by using a small function to convert version strings to plain integer values that can be compared:
function versionToInt() {
local IFS=.
parts=($1)
let val=1000000*parts[0]+1000*parts[1]+parts[2]
echo $val
}
This makes two important assumptions:
For example
versionToInt 12.34.56 # --> 12034056
versionToInt 1.2.3 # --> 1002003
Example testing whether npm
command meets minimum requirement ...
NPM_ACTUAL=$(versionToInt $(npm --version)) # Capture npm version
NPM_REQUIRED=$(versionToInt 4.3.0) # Desired version
if [ $NPM_ACTUAL \< $NPM_REQUIRED ]; then
echo "Please update to npm@latest"
exit 1
fi
This code can also compare floats. It is using awk (it is not pure bash), however this shouldn't be a problem, as awk is a standard POSIX command that is most likely shipped by default with your operating system.
$ awk 'BEGIN {return_code=(-1.2345 == -1.2345) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
0
$ awk 'BEGIN {return_code=(-1.2345 >= -1.2345) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
0
$ awk 'BEGIN {return_code=(-1.2345 < -1.2345) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
1
$ awk 'BEGIN {return_code=(-1.2345 < 2) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
0
$ awk 'BEGIN {return_code=(-1.2345 > 2) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
To make it shorter for use, use this function:
compare_nums()
{
# Function to compare two numbers (float or integers) by using awk.
# The function will not print anything, but it will return 0 (if the comparison is true) or 1
# (if the comparison is false) exit codes, so it can be used directly in shell one liners.
#############
### Usage ###
### Note that you have to enclose the comparison operator in quotes.
#############
# compare_nums 1 ">" 2 # returns false
# compare_nums 1.23 "<=" 2 # returns true
# compare_nums -1.238 "<=" -2 # returns false
#############################################
num1=$1
op=$2
num2=$3
E_BADARGS=65
# Make sure that the provided numbers are actually numbers.
if ! [[ $num1 =~ ^-?[0-9]+([.][0-9]+)?$ ]]; then >&2 echo "$num1 is not a number"; return $E_BADARGS; fi
if ! [[ $num2 =~ ^-?[0-9]+([.][0-9]+)?$ ]]; then >&2 echo "$num2 is not a number"; return $E_BADARGS; fi
# If you want to print the exit code as well (instead of only returning it), uncomment
# the awk line below and comment the uncommented one which is two lines below.
#awk 'BEGIN {print return_code=('$num1' '$op' '$num2') ? 0 : 1; exit} END {exit return_code}'
awk 'BEGIN {return_code=('$num1' '$op' '$num2') ? 0 : 1; exit} END {exit return_code}'
return_code=$?
return $return_code
}
$ compare_nums -1.2345 ">=" -1.2345 && echo true || echo false
true
$ compare_nums -1.2345 ">=" 23 && echo true || echo false
false
Like this:
#!/bin/bash
a=2462620
b=2462620
if [ "$a" -eq "$b" ]; then
echo "They're equal";
fi
Integers can be compared with these operators:
-eq # equal
-ne # not equal
-lt # less than
-le # less than or equal
-gt # greater than
-ge # greater than or equal
See this cheatsheet: https://devhints.io/bash#conditionals
Source: Stackoverflow.com