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--- floating_point_calculation [2012/01/27 16:02]
k2patel
+++ floating_point_calculation [2012/01/27 16:34]
k2patel [Using in Script for Comparision]
@@ Line 1: / Line 1: @@
 ====== Floating Point Calculation ======
 This is an example represent how to compute Floating point in bash.
+==== Using in Script for Comparision ====
+To use ''bc'' in our bash scripts we'll package it up into a couple of functions:
+<code oobas>
+    float_eval EXPRESSION
+and
+    float_cond CONDITIONAL-EXPRESSION
+</code>
+Both functions expect a single floating point expression, ''float_eval'' writes the result of the expression evaluation to standard out, ''float_cond'' assumes the expression is a conditional expression and sets the return/status code to zero if the expression is true and one if it's false.
+Usage is quite simple:
+<code oobas>
+  float_eval '12.0 / 3.0'
+  if float_cond '10.0 > 9.0'; then
+    echo 'As expected, 10.0 is greater than 9.0'
+  fi
+  a=12.0
+  b=3.0
+  c=$(float_eval "$a / $b")
+</code>
+The code for the functions follows:
+<code bash>
+#!/bin/bash
+#
+# Floating point number functions.
+#####################################################################
+# Default scale used by float functions.
+float_scale=2
+#####################################################################
+# Evaluate a floating point number expression.
+function float_eval()
+{
+    local stat=0
+    local result=0.0
+    if [[ $# -gt 0 ]]; then
+        result=$(echo "scale=$float_scale; $*" | bc -q 2>/dev/null)
+        stat=$?
+        if [[ $stat -eq 0  &&  -z "$result" ]]; then stat=1; fi
+    fi
+    echo $result
+    return $stat
+}
+#####################################################################
+# Evaluate a floating point number conditional expression.
+function float_cond()
+{
+    local cond=0
+    if [[ $# -gt 0 ]]; then
+        cond=$(echo "$*" | bc -q 2>/dev/null)
+        if [[ -z "$cond" ]]; then cond=0; fi
+        if [[ "$cond" != 0  &&  "$cond" != 1 ]]; then cond=0; fi
+    fi
+    local stat=$((cond == 0))
+    return $stat
+}
+# Test code if invoked directly.
+if [[ $(basename $0 .sh) == 'float' ]]; then
+    # Use command line arguments if there are any.
+    if [[ $# -gt 0 ]]; then
+        echo $(float_eval $*)
+    else
+        # Turn off pathname expansion so * doesn't get expanded
+        set -f
+        e="12.5 / 3.2"
+        echo $e is $(float_eval "$e")
+        e="100.4 / 4.2 + 3.2 * 6.5"
+        echo $e is $(float_eval "$e")
+        if float_cond '10.0 > 9.3'; then
+            echo "10.0 is greater than 9.3"
+        fi
+        if float_cond '10.0 < 9.3'; then
+            echo "Oops"
+        else
+            echo "10.0 is not less than 9.3"
+        fi
+        a=12.0
+        b=3.0
+        c=$(float_eval "$a / $b")
+        echo "$a / $b" is $c
+        set +f
+    fi
+fi
+# vim: tabstop=4: shiftwidth=4: noexpandtab:
+# kate: tab-width 4; indent-width 4; replace-tabs false;
+</code>
+The work of the functions is done by feeding the arguments to ''bc'':
+<code oobas>
+   result=$(echo "scale=$float_scale; $*" | bc -q 2>/dev/null)
+</code>
+By default ''bc'' outputs its result with no digits to the right of the decimal point and without a decimal point. To change this you have to change one of ''bc'''s builtin variables: ''scale''. This is where the "language" features of ''bc'' are relevant, in ''bc'' as in C statements are separated by semi-colons. We set ''bc'''s ''scale'' variable by preceding the expression that we pass to ''bc'' with ''scale=$float_scale;''. This sets the scale in ''bc'' to the value of the bash global variable ''float_scale'', which is by default set to two (near the top of the script).
+The main gotcha here has to do with the fact that "*", "<", and ">" have other meanings in bash. You can eliminate the problem of "<" and ">" by quoting your expressions, but this only works with "*" if you use single quotes and that would mean you couldn't include bash variables in the expression. The other option is to bracket your code with "''set -f''" and "''set +f''" to turn off pathname/wildcard expansion.
+If you save the script as ''float.sh'' and run it directly it will execute the test code at the bottom:
+<code oobas>
+  $ sh float.sh
+.5 / 3.2 is 3.90
+.4 / 4.2 + 3.2 * 6.5 is 44.70
+.0 is greater than 9.3
+.0 is not less than 9.3
+.0 / 3.0 is 4.00
+</code>
+The one unaswered question you may have is: "and why would I want to do this?" Next time around I'll show you one place you can put this to real world use.
+Ref : [[ http://www.linuxjournal.com/content/floating-point-math-bash | Linux Journal ]]
+==== Doing Calculation ====
 **Details**
@@ Line 129: / Line 254: @@
 </code>
-Ref. [[http://www.novell.com/coolsolutions/tools/17043.html|http://www.novell.com/coolsolutions/tools/17043.html]]
+Ref. [[ http://www.novell.com/coolsolutions/tools/17043.html | Novell Cool Solutions ]]

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