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Full Discussion: compare variable against regular expression?
Top Forums Shell Programming and Scripting compare variable against regular expression? Post 302198036 by era on Thursday 22nd of May 2008 06:20:17 AM
Old 05-22-2008
The if command simply evaluates another command, and examines its exit code to decide whether to take the then branch or the else branch (if present). You can use the expr command to match a string against a regular expression, or echo | grep. I would recommend case for this, though, even if it actually uses glob expressions, not true regular expressions.

Some shells also have built-in regex operators with the [[ conditional ]] syntax.

Code:
if echo "$var" | grep '[^0-9]'; then
  echo not a number  
fi
if expr "$var" : '[^0-9]' >/dev/null; then
  echo not a number
fi
case $var in
  *[!0-9]*) echo not a number;;    # not a regex proper
esac
if [[ "$var" =~ [^0-9] ]] ; then
  echo not a number
fi

All of these are more or less functionally equivalent. (They will not reject an empty string as not a number; implementing that is left as an exercise.)
Last edited by era; 05-22-2008 at 07:23 AM.. Reason: Will accept empty string as well as numbers, actually
 

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LEARN ABOUT PHP

boolval

BOOLVAL(3)								 1								BOOLVAL(3)

boolval - Get the boolean value of a variable

SYNOPSIS

       boolean boolval (mixed  $var)

DESCRIPTION

	Returns the boolean value of $var.

PARAMETERS

	      o $var
		- The scalar value being converted to a boolean.

RETURN VALUES

	The boolean value of $var.

EXAMPLES

       Example #1

	      boolval(3) examples

	      <?php
	      echo '0:	      '.(boolval(0) ? 'true' : 'false')."
";
	      echo '42:       '.(boolval(42) ? 'true' : 'false')."
";
	      echo '0.0:      '.(boolval(0.0) ? 'true' : 'false')."
";
	      echo '4.2:      '.(boolval(4.2) ? 'true' : 'false')."
";
	      echo '"":       '.(boolval("") ? 'true' : 'false')."
";
	      echo '"string": '.(boolval("string") ? 'true' : 'false')."
";
	      echo '"0":      '.(boolval("0") ? 'true' : 'false')."
";
	      echo '"1":      '.(boolval("1") ? 'true' : 'false')."
";
	      echo '[1, 2]:   '.(boolval([1, 2]) ? 'true' : 'false')."
";
	      echo '[]:       '.(boolval([]) ? 'true' : 'false')."
";
	      echo 'stdClass: '.(boolval(new stdClass) ? 'true' : 'false')."
";
	      ?>

	      The above example will output:

	      0:	false
	      42:	true
	      0.0:	false
	      4.2:	true
	      "":	false
	      "string": true
	      "0":	false
	      "1":	true
	      [1, 2]:	true
	      []:	false
	      stdClass: true

SEE ALSO

       floatval(3), intval(3), strval(3), settype(3), is_bool(3), Type juggling.

PHP Documentation Group 														BOOLVAL(3)
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