my case is very simple:
I am trying to compare two values:
a=0.2
b=0.1
The code that I am trying to execute is:
if [ "$a" -gt "$b" ]; then
echo "You are running an outdated version"
fi
Assuming you want to compare version numbers, would you please try the following:
#!/bin/bash -posix
# compares version numbers
# prints 0 if $a == $b
# positive number if $a is newer than $b
# negative number if $a is older than $b
vercmp() {
local a=$1
local b=$2
local a1=${a%%.*} # major number of $a
local b1=${b%%.*} # major number of $b
if [[ $a = "" ]]; then
if [[ $b = "" ]]; then
echo 0 # both $a and $b are empty
else
vercmp "0" "$b"
fi
elif [[ $b = "" ]]; then
vercmp "$a" "0"
elif (( 10#$a1 == 10#$b1 )); then
local a2=${a#*.} # numbers after the 1st dot
if [[ $a2 = $a ]]; then
a2="" # no more version numbers
fi
local b2=${b#*.} # numbers after the 1st dot
if [[ $b2 = $b ]]; then
b2="" # no more version numbers
fi
vercmp "$a2" "$b2"
else
echo $(( 10#$a1 - 10#$b1 ))
fi
}
Examples:
vercmp 0.2 0.1
=> 1 (positive number: the former is newer)
vercmp 1.0.2 1.0.10
=> -8 (negative number: the latter is newer)
a=0.2
b=0.1
if (( $(vercmp "$a" "$b") > 0 )); then
echo "You are running an outdated version"
fi
Related
I'm unable to get numeric comparisons working:
echo "enter two numbers";
read a b;
echo "a=$a";
echo "b=$b";
if [ $a \> $b ];
then
echo "a is greater than b";
else
echo "b is greater than a";
fi;
The problem is that it compares the number from the first digit on, i.e., 9 is bigger than 10, but 1 is greater than 09.
How can I convert the numbers into a type to do a true comparison?
In Bash, you should do your check in an arithmetic context:
if (( a > b )); then
...
fi
For POSIX shells that don't support (()), you can use -lt and -gt.
if [ "$a" -gt "$b" ]; then
...
fi
You can get a full list of comparison operators with help test or man test.
Like this:
#!/bin/bash
a=2462620
b=2462620
if [ "$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.
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
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 stuff like
(( (n + 1) > m ))
But everyone just has their own preferences. Sad thing is that some people impose their unofficial standards.
You can also do this:
[[ 'n + 1' -gt m ]]
Which allows you to add something else which you could do with [[ ]] besides arithmetic stuff.
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.
One-line solution.
a=2
b=1
[[ ${a} -gt ${b} ]] && echo "true" || echo "false"
gt reference: https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html
&& reference: https://www.gnu.org/software/bash/manual/html_node/Shell-Arithmetic.html
[[...]] construct reference: https://www.gnu.org/software/bash/manual/bash.html#index-_005b_005b
${} reference: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02 (2.6.2)
The format for parameter expansion is as follows:
${expression}
where expression consists of all characters until the matching '}'.
Any '}' escaped by a or within a quoted string, and
characters in embedded arithmetic expansions, command substitutions,
and variable expansions, shall not be examined in determining the
matching '}'.
The simplest form for parameter expansion is:
${parameter}
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
If you have floats, you can write a function and then use that. For example,
#!/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
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 $val
}
This makes two important assumptions:
The input is a "normal SemVer string"
Each part is between 0-999
For example
versionToInt 12.34.56 # --> 12034056
versionToInt 1.2.3 # --> 1002003
Example testing whether npm command meets the minimum requirement...
NPM_ACTUAL=$(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
Just adding to all the above answers:
If you have more than one expression in single if statement, you can do something like this:
if (( $a % 2 == 0 )) && (( $b % 2 != 0));
then
echo "What you want to do"
fi
Hope this helps!
I'm unable to get numeric comparisons working:
echo "enter two numbers";
read a b;
echo "a=$a";
echo "b=$b";
if [ $a \> $b ];
then
echo "a is greater than b";
else
echo "b is greater than a";
fi;
The problem is that it compares the number from the first digit on, i.e., 9 is bigger than 10, but 1 is greater than 09.
How can I convert the numbers into a type to do a true comparison?
In Bash, you should do your check in an arithmetic context:
if (( a > b )); then
...
fi
For POSIX shells that don't support (()), you can use -lt and -gt.
if [ "$a" -gt "$b" ]; then
...
fi
You can get a full list of comparison operators with help test or man test.
Like this:
#!/bin/bash
a=2462620
b=2462620
if [ "$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.
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
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 stuff like
(( (n + 1) > m ))
But everyone just has their own preferences. Sad thing is that some people impose their unofficial standards.
You can also do this:
[[ 'n + 1' -gt m ]]
Which allows you to add something else which you could do with [[ ]] besides arithmetic stuff.
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.
One-line solution.
a=2
b=1
[[ ${a} -gt ${b} ]] && echo "true" || echo "false"
gt reference: https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html
&& reference: https://www.gnu.org/software/bash/manual/html_node/Shell-Arithmetic.html
[[...]] construct reference: https://www.gnu.org/software/bash/manual/bash.html#index-_005b_005b
${} reference: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02 (2.6.2)
The format for parameter expansion is as follows:
${expression}
where expression consists of all characters until the matching '}'.
Any '}' escaped by a or within a quoted string, and
characters in embedded arithmetic expansions, command substitutions,
and variable expansions, shall not be examined in determining the
matching '}'.
The simplest form for parameter expansion is:
${parameter}
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
If you have floats, you can write a function and then use that. For example,
#!/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
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 $val
}
This makes two important assumptions:
The input is a "normal SemVer string"
Each part is between 0-999
For example
versionToInt 12.34.56 # --> 12034056
versionToInt 1.2.3 # --> 1002003
Example testing whether npm command meets the minimum requirement...
NPM_ACTUAL=$(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
Just adding to all the above answers:
If you have more than one expression in single if statement, you can do something like this:
if (( $a % 2 == 0 )) && (( $b % 2 != 0));
then
echo "What you want to do"
fi
Hope this helps!
I am trying to write a bash script to find if a number is prime, but i can't find what is wrong with my script
#!/bin/bash
#set -x
echo -n "enter a number "
read isPrime
count=2
x=0
while [ $count -lt $isPrime ]; do
if [ `expr $isPrime % $count`-eq 0 ]; then
echo "not prime"
fi
count=`expr $count + 1`
done
echo " it is prime"
#set +x
Using factor would be easy. But if you somehow need a script, I would implement something like following. I'm not sure whether this is the best algorithm, but this is way efficient than yours.
function is_prime(){
if [[ $1 -eq 2 ]] || [[ $1 -eq 3 ]]; then
return 1 # prime
fi
if [[ $(($1 % 2)) -eq 0 ]] || [[ $(($1 % 3)) -eq 0 ]]; then
return 0 # not a prime
fi
i=5; w=2
while [[ $((i * i)) -le $1 ]]; do
if [[ $(($1 % i)) -eq 0 ]]; then
return 0 # not a prime
fi
i=$((i + w))
w=$((6 - w))
done
return 1 # prime
}
# sample usage
is_prime 7
if [[ $? -eq 0 ]]; then
echo "not a prime"
else
echo "it's a prime"
fi
You can find an explanation about the used algorithm here
In the following code I want to compare the command line arguments with the parameters but I am not sure what is the current syntax to compare the arguments with parameters..i.e "==" or "-eq".
#!/bin/bash
argLength=$#
#echo "arg = $1"
if [ argLength==0 ]; then
#Running for the very first
#Get the connected device ids and save it in an array
N=0
CONNECTED_DEVICES=$(adb devices | grep -o '\b[A-Za-z0-9]\{8,\}\b'|sed -n '2,$p')
NO_OF_DEVICES=$(echo "$CONNECTED_DEVICES" | wc -l)
for CONNECTED_DEVICE in $CONNECTED_DEVICES ; do
DEVICE_IDS[$N]="$CONNECTED_DEVICE"
echo "DEVICE_IDS[$N]= $CONNECTED_DEVICE"
let "N= $N + 1"
done
for SEND_DEVICE_ID in ${DEVICE_IDS[#]} ; do
callCloneBuildInstall $SEND_DEVICE_ID
done
elif [ "$1" -eq -b ]; then
if [ $5 -eq pass ]; then
DEVICE_ID=$3
./MonkeyTests.sh -d $DEVICE_ID
else
sleep 1h
callCloneBuildInstall $SEND_DEVICE_ID
fi
elif [ "$1" -eq -m ]; then
echo "Check for CloneBuildInstall"
if [ "$5" -eq pass ]; then
DEVICE_ID=$3
callCloneBuildInstall $SEND_DEVICE_ID
else
echo "call CloneBuildInstall"
# Zip log file and save it with deviceId
callCloneBuildInstall $SEND_DEVICE_ID
fi
fi
function callCloneBuildInstall {
./CloneBuildInstall.sh -d $SEND_DEVICE_ID
}
From help test:
[...]
STRING1 = STRING2
True if the strings are equal.
[...]
arg1 OP arg2 Arithmetic tests. OP is one of -eq, -ne,
-lt, -le, -gt, or -ge.
But in any case, each part of the condition is a separate argument to [.
if [ "$arg" -eq 0 ]; then
if [ "$arg" = 0 ]; then
Why not use something like
if [ "$#" -ne 0 ]; then # number of args should not be zero
echo "USAGE: "
fi
When/how to use “==” or “-eq” operator in test?
To put it simply use == when doing lexical comparisons a.k.a string comparisons but use -eq when having numerical comparisons.
Other forms of -eq (equal) are -ne (not equal), -gt (greater than), -ge (greater than or equal), -lt (lesser than), and -le (lesser than or equal).
Some may also suggest preferring (( )).
Examples:
[[ $string == "something else" ]]
[[ $string != "something else" ]] # (negated)
[[ $num -eq 1 ]]
[[ $num -ge 2 ]]
(( $num == 1 ))
(( $num >= 1 ))
And always use [[ ]] over [ ] when you're in Bash since the former skips unnecessary expansions not related to conditional expressions like word splitting and pathname expansion.
the following example shows hot to compare numbers
I give here two different ways
one way with the ">" and "<"
and second way with "-gt" or "-lt"
both ways are work exactly
so what the differences between them ? or maybe there are not difference ?
example 1
ksh
a=1
b=2
[[ $a > $b ]] && echo ok
[[ $a < $b ]] && echo ok
ok
example 2
ksh
a=1
b=2
[[ $a -gt $b ]] && echo ok
[[ $a -lt $b ]] && echo ok
ok
In your examples there are no difference, but that is just an unfortunate choice of values for a and b.
-lt, -gt are for numeric comparison
< and > are for alphabetic comparison
$ a=12
$ b=6
$ [[ $a -lt $b ]] && echo ok
$ [[ $a < $b ]] && echo ok
ok