Shell Programming and Scripting

echo $(echo "1.8 >= 2.0" | bc)
0

echo $(echo "2.0 >= 2.0" | bc)
1

echo $(echo "1.9.1 >= 2.0" | bc)
(standard_in) 1: syntax error

# String comparison. This is not a numeric comparison
if [ "2.0" = "2.0" ]
then
      echo "1"
else
      echo "0"
fi

#!/usr/bin/env bash

# @(#) user4	Compare version numbers of form a.b.c.
# Adapted from post # 10.
# https://www.unix.com/unix-dummies-questions-answers/
# 93739-comparing-version-numbers.html#post302269675

pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && $C

# compare version numbers
# usage: vercmp <versionnr1> <versionnr2>
#         with format for versions xxx.xxx.xxx
# returns: 0 if versionnr1 equal or greater
#          1 if versionnr1 lower

vercmp()
{
  local a1 b1 c1 a2 b2 c2
  # echo|read succeeds in ksh, but fails in bash.
  # bash alternative is "set --"
  db "input 1 \"$1\", 2 \"$2\" " 
  v1=$1
  v2=$2
  db "v1 $v1, v2 $v2"
  set -- $( echo "$v1" | sed 's/\./ /g' )
  a1=$1 b1=$2 c1=$3
  set -- $( echo "$v2" | sed 's/\./ /g' )
  a2=$1 b2=$2 c2=$3
  db "a1,b1,c1 $a1,$b1,$c1 ; a2,b2,c2 $a2,$b2,$c2"
  ret=$(( (a1-a2)*1000000+(b1-b2)*1000+c1-c2 ))
  db "ret is $ret"
  if [ $ret -lt 0 ] ; then
    v=-1
  elif [ $ret -eq 0 ] ; then
    v=0
  else
    v=1
  fi
  printf "%d" $v
  return
}

FILE=${1-data1}

while read a b
do
  pe
  pe " Comparing version strings \"$a\" and \"$b\""
  v=$( vercmp $a $b )
  db "vercmp returns $v"
  if [ $v -lt 0 ]
  then
    pe " $a is earlier than $b"
  elif [ $v -eq 0 ]
  then
    pe " Versions are equal"
  else
    pe " $a is later than $b"
  fi
done <$FILE

exit 0

% ./user4

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0.8 (lenny) 
bash GNU bash 3.2.39

 Comparing version strings "1.1.0" and "1.1.1"
 1.1.0 is earlier than 1.1.1

 Comparing version strings "2.2.2" and "2.2.1"
 2.2.2 is later than 2.2.1

 Comparing version strings "3.3.9" and "3.4.1"
 3.3.9 is earlier than 3.4.1

 Comparing version strings "3.5.0" and "3.5.0"
 Versions are equal

 Comparing version strings "1.9.2" and "2.0"
 1.9.2 is earlier than 2.0