How can I compare floating number in a shell script?

ydrol · 04-26-2010, 09:16 AM

'bc' mentioned 2005 and 2008
Only issue is

Quote:

# echo "2.2 > 1.1" | bc
/bin/sh: bc: not found

Hence other discussion.

catkin · 04-26-2010, 10:21 AM

Which distro are you using, that doesn't have bc? Or is your $PATH set OK? On Slackware 13.0:

Code:

c@CW8:~$ type bc
bc is /usr/bin/bc

ydrol · 04-26-2010, 10:25 AM

as mentioned here

"eg many small devices running busybox"

# uname -a
Linux hdx 2.6.15-sigma #953 PREEMPT Wed Jun 3 21:49:15 CST 2009 mips GNU/Linux

# busybox
BusyBox v1.14.1 (2009-06-21 11:33:51 CEST) multi-call binary
Copyright (C) 1998-2008 Erik Andersen, Rob Landley, Denys Vlasenko
and others. Licensed under GPLv2.
See source distribution for full notice.

Usage: busybox [function] [arguments]...
or: function [arguments]...

BusyBox is a multi-call binary that combines many common Unix
utilities into a single executable. Most people will create a
link to busybox for each function they wish to use and BusyBox
will act like whatever it was invoked as!

Currently defined functions:
[, [[, addgroup, adduser, adjtimex, ar, arp, arping, ash,
awk, basename, bbconfig, blkid, brctl, bunzip2, bzcat, bzip2,
cal, cat, catv, chat, chattr, chgrp, chmod, chown, chpasswd,
chpst, chroot, chrt, chvt, cksum, clear, cmp, comm, cp,
cpio, crond, crontab, cryptpw, cttyhack, cut, date, dc,
dd, deallocvt, delgroup, deluser, depmod, devmem, df, dhcprelay,
diff, dirname, dmesg, dnsd, dos2unix, dpkg, dpkg-deb, du,
dumpkmap, dumpleases, echo, ed, egrep, eject, env, envdir,
envuidgid, ether-wake, expand, expr, fakeidentd, false,
fbset, fbsplash, fdflush, fdformat, fdisk, fgrep, find,
findfs, fold, free, freeramdisk, fsck, fsck.minix, ftpd,
ftpget, ftpput, fuser, getopt, getty, grep, gunzip, gzip,
halt, hd, hdparm, head, hexdump, hostid, hostname, httpd,
hush, hwclock, id, ifconfig, ifdown, ifenslave, ifup, inetd,
init, insmod, install, ip, ipaddr, ipcalc, ipcrm, ipcs,
iplink, iproute, iprule, iptunnel, kbd_mode, kill, killall,
killall5, klogd, last, length, less, linux32, linux64, linuxrc,
ln, loadfont, loadkmap, logger, login, logname, logread,
losetup, lpd, lpq, lpr, ls, lsattr, lsmod, lzmacat, makedevs,
makemime, man, md5sum, mdev, mesg, microcom, mkdir, mkdosfs,
mkfifo, mkfs.minix, mkfs.vfat, mknod, mkpasswd, mkswap,
mktemp, modprobe, more, mount, mountpoint, mt, mv, nameif,
nc, netstat, nice, nmeter, nohup, nslookup, od, openvt,
passwd, patch, pgrep, pidof, ping, ping6, pipe_progress,
pivot_root, pkill, popmaildir, poweroff, printenv, printf,
ps, pscan, pwd, raidautorun, rdate, rdev, readahead, readlink,
readprofile, realpath, reboot, reformime, renice, reset,
resize, rm, rmdir, rmmod, route, rpm, rpm2cpio, rtcwake,
run-parts, runlevel, runsv, runsvdir, rx, script, sed, sendmail,
seq, setarch, setconsole, setfont, setkeycodes, setlogcons,
setsid, setuidgid, sh, sha1sum, sha256sum, sha512sum, showkey,
slattach, sleep, softlimit, sort, split, start-stop-daemon,
stat, strings, stty, su, sulogin, sum, sv, svlogd, swapoff,
swapon, switch_root, sync, sysctl, syslogd, tac, tail, tar,
tcpsvd, tee, telnet, telnetd, test, tftp, tftpd, time, timeout,
top, touch, tr, traceroute, true, tty, ttysize, tunctl,
udhcpc, udhcpd, udpsvd, umount, uname, uncompress, unexpand,
uniq, unix2dos, unlzma, unzip, uptime, usleep, uudecode,
uuencode, vconfig, vi, vlock, watch, watchdog, wc, wget,
which, who, whoami, xargs, yes, zcat, zcip

catkin · 04-26-2010, 10:59 AM

Quote:

Originally Posted by ydrol

as mentioned here

Sorry -- I missed that

frater · 11-05-2010, 02:34 AM

Although some of the examples given in this thread do work (not all), I always strive to use syntax that is as human readable as possible.

Code:

x=3.3
y=3.2
if expr $x \> $y >/dev/null ; then
 echo "the value of x ($x) is greater than y ($y)"
else
 echo "the value of x ($x) is NOT greater than y ($y)"
fi

so it's as simple as this:

Code:

x=3.3
y=3.2
expr $x \> $y >/dev/null && echo "$x > $y"

And even busybox supports it:

Code:

busybox | grep -o expr
expr

Alas `expr` doesn't support a '-q' (quiet) so we need to pipe the output to /dev/null and only use the errorlevel it returns

VinPhend · 11-30-2010, 02:24 PM

I am happy with

Quote:

Originally Posted by Galogen

compare_result=`echo "2.2 > 1.1" | bc`
if [ $compare_result ]; then
echo 1
fi

My full script:

Code:

#!/bin/bash 
#Select group of plots by part of filename.
outputdir="last-selected"

#SEARCH="spacer:+0.095"
SEARCH="WG-width:0.190"
echo $SEARCH
ls *.png | grep $SEARCH > list.txt
rm -r $outputdir
mkdir $outputdir
mkdir $SEARCH
while IFS= read -r file
    do
    echo $file
    cp $file $outputdir
    done < "list.txt"  
cd $outputdir

#remove visually similar images
ls *.png | grep $SEARCH > listi.txt
ls *.png | grep $SEARCH > listj.txt
while IFS= read -r i;    do
    while IFS= read -r j; do
        #distanse between images in similarity space, float number
	result=$(puzzle-diff $i $j) 
	threshold=0.2
        #if not the same
	if [ "$result" != "0" ]
	then
	    check=`echo "$result<$threshold" | bc`
	    if [ "$check"  !=  "0" ]
	    then
                #remove similar
		rm $j
		ls *.png  > listi.txt
		ls *.png  > listj.txt
	    fi
	fi
    done < "listi.txt"  
done < "listj.txt"  
cd ../
cp -r $outputdir/*.png $SEARCH

catkin · 11-30-2010, 07:44 PM

I'm happy you are happy

Threads can be marked SOLVED using the Thread Tools menu.

bytecode · 07-20-2011, 04:16 PM

For those stumbling upon this thread in the future:

Actually, it's even simpler than Fraters excellent solution if using BASH, as there is no need for "expr" - provided that:
1) you remember to ESCAPE the "<" or ">" operators with a slash "\"
and
2) the length of the floats is the same, e.g. "4.0 \< 5.0" or "40.5" \< "50.5" as it'll still be a string compare... (Otherwise you will need to use expr, as "4.0 \< 60.3"

Code:

byte@bluepoolinternet.com:/home/byte$ if [ 4.0 \< 5.0 ]; then echo TRUE; else echo FALSE; fi
TRUE
byte@bluepoolinternet.com:/home/byte$ if [ 6.0 \< 5.0 ]; then echo TRUE; else echo FALSE; fi
FALSE

It can get quite interesting with string datatypes...

If anyone is wondering why the original response from Moneycat failed:

Quote:

Originally Posted by MoneyCat

This is because the -lt, -gt, -le, -ge, comparisons are only designed for integers. Try using these operators: >, <, >=, <=

It is because by default, in BASH, the >, < operators are RE-DIRECTION Operators, for redirecting output to files etc. so to use them in the test expression, you have to escape them, otherwise you get the confusing error re no such file or directory:

Code:

byte@bluepoolinternet.com:/home/byte$ if [ 4 < 5 ]; then echo TRUE; fi
bash: 5: No such file or directory

as the BASH interpreter is making the natural assumption that the "5" is a file, and would also have assumed that the "4" was a file also.
Obviously, once you realise that it's a real "D'oh!" moment ;-)

Quote:

Originally Posted by frater

Although some of the examples given in this thread do work (not all), I always strive to use syntax that is as human readable as possible.

Code:

x=3.3
y=3.2
if expr $x \> $y >/dev/null ; then
 echo "the value of x ($x) is greater than y ($y)"
else
 echo "the value of x ($x) is NOT greater than y ($y)"
fi

so it's as simple as this:

Code:

x=3.3
y=3.2
expr $x \> $y >/dev/null && echo "$x > $y"

And even busybox supports it:

Code:

busybox | grep -o expr
expr

Alas `expr` doesn't support a '-q' (quiet) so we need to pipe the output to /dev/null and only use the errorlevel it returns

chrism01 · 07-20-2011, 08:32 PM

Strictly speaking, '< > = == ... ' are string operators, '-eq -ne -lt ...' are numeric operators (in a test statement) in bash, ksh etc.
See table B2 http://www.tldp.org/LDP/abs/html/refcards.html#AEN22078 and note this changes inside (( )) arithmetic brackets.

The issue here is [ ] vs [[ ]] http://tldp.org/LDP/abs/html/testcon...ml#DBLBRACKETS

Code:

if [[ 4 < 5 ]]; then echo TRUE; fi
TRUE

bytecode · 07-21-2011, 04:16 AM

Ah, yes - I wasn't aware of the double [[ ]] context with regards to escaping.
Now, If only we can get around the string data type issue whereby this unexpectedly returns TRUE:

Code:

$ if [[ 40.0 < 5.0 ]]; then echo TRUE; else echo FALSE; fi
TRUE

Of course the fun with (( )) is again that we often want to compare floats, if comparing with say, CPU or MEM% use of a process etc..
I suppose we could always go for integer arithmetic; multiply by 100 and discard the decimal fractional component?

Any further tips chrism01?
=)

Quote:

Originally Posted by chrism01

Strictly speaking, '< > = == ... ' are string operators, '-eq -ne -lt ...' are numeric operators (in a test statement) in bash, ksh etc.
See table B2 http://www.tldp.org/LDP/abs/html/refcards.html#AEN22078 and note this changes inside (( )) arithmetic brackets.

The issue here is [ ] vs [[ ]] http://tldp.org/LDP/abs/html/testcon...ml#DBLBRACKETS

Code:

if [[ 4 < 5 ]]; then echo TRUE; fi
TRUE

frater · 11-26-2011, 03:19 AM

I don't know what's worse... someone else telling you that you are wrong or yourself..

But it now seems that 'expr' isn't suitable to compare "floating numbers"

Code:

# x=3.3
# y=3.2
# expr $x \> $y >/dev/null && echo "$x > $y"
3.3 > 3.2
# x=4
# y=3.2
# expr $x \> $y >/dev/null && echo "$x > $y"
4 > 3.2
# x=10
# y=3
# expr $x \> $y >/dev/null && echo "$x > $y"
10 > 3
# x=10
# y=3.2
# expr $x \> $y >/dev/null && echo "$x > $y"
#

Although it doesn't give an error, it doesn't work in the last case....
I guess you can do it better with awk....

bytecode · 11-27-2011, 02:24 PM

Quote:

Originally Posted by frater

I don't know what's worse... someone else telling you that you are wrong or yourself..

But it now seems that 'expr' isn't suitable to compare "floating numbers"

Code:

# x=3.3
# y=3.2
# expr $x \> $y >/dev/null && echo "$x > $y"
3.3 > 3.2
# x=4
# y=3.2
# expr $x \> $y >/dev/null && echo "$x > $y"
4 > 3.2
# x=10
# y=3
# expr $x \> $y >/dev/null && echo "$x > $y"
10 > 3
# x=10
# y=3.2
# expr $x \> $y >/dev/null && echo "$x > $y"
#

Although it doesn't give an error, it doesn't work in the last case....
I guess you can do it better with awk....

Or we're back to "bc" again...

Juako · 11-28-2011, 07:23 PM

A few weeks ago I wrote this one to compare floats in bash, it handles negatives too:

Code:

#!/bin/bash
shopt -s extglob
fcomp() {
    local oldIFS="$IFS" op=$2 x y digitx digity
    IFS='.' x=( ${1##+([0]|[-]|[+])}) y=( ${3##+([0]|[-]|[+])}) IFS="$oldIFS"
    while [[ "${x[1]}${y[1]}" =~ [^0] ]]; do
        digitx=${x[1]:0:1} digity=${y[1]:0:1}
        (( x[0] = x[0] * 10 + ${digitx:-0} , y[0] = y[0] * 10 + ${digity:-0} ))
        x[1]=${x[1]:1} y[1]=${y[1]:1} 
    done
    [[ ${1:0:1} == '-' ]] && (( x[0] *= -1 ))
    [[ ${3:0:1} == '-' ]] && (( y[0] *= -1 ))
    (( ${x:-0} $op ${y:-0} ))
}

for op in '==' '!=' '>' '<' '<=' '>='; do
    fcomp $1 $op $2 && echo "$1 $op $2"
done

Edit:
sorry I forgot to explain how it works, it works essentially by shifting the point until both numbers are ints (ie, iterate: int_part * 10 + shifted decimal digit).

Its a bit verbose to take into account some oddities, such as numbers with leftmost zeroes at the int part or rightmost zeroes at the decimal part, and signed numbers. If you don't use signs you can dismiss the two lines before the last in fcomp():

Code:

    [[ ${1:0:1} == '-' ]] && (( x[0] *= -1 ))
    [[ ${3:0:1} == '-' ]] && (( y[0] *= -1 ))

And shorten the patterns at x and y array creation to:

Code:

    IFS='.' x=( ${1##+([0])} ) y=( ${3##+([0])} ) IFS="$oldIFS"

so it just wipes the leftmost zeroes.

hayko · 09-10-2012, 08:43 AM

Hi
Please help me.
I have file which contains
60
59
52
45
43
40
70
69
62
which bash script can give me "pass on every line and every time remembering previous number give me the first mutch where next number greater than previous, in this example 70"
Please help thank you.

theNbomr · 09-10-2012, 11:29 AM

This should get you started:

Code:

read xOld < LQhayko.dat; 
while read xNew; do 
    echo $xNew; 
    if [ $xNew -gt $xOld ]; then 
        echo "Found rising edge: $xNew > $xOld"; 
        break;
    else 
        xOld=$xNew; 
    fi;  
done < LQhayko.dat

--- rod.

PS. This should have been posted as a new thread. Necroposting and thread hijacking are considered poor form here.