纠结的bash/perl 数值/字符比较

时间：2010-11-15 来源：ubuntuer

perl 跟 bash刚好相反。。。。

Perl comparison
Refer to http://ist.marshall.edu/ist334/perl_basics.html

Numerical Comparison
<	less than	$bad = $gpa < 1.5;
<=	less than or equal	$good = 3.5 <= $gpa;
>	greater than	$very_good = $gpa > 3.9;
>=	greater than or equal	$not_bad = $gpa >= 2.3;
==	equals to	$perfect = $gpa == 4;
!=	not equal to	$not_perfect = $gpa != 4;
<=>	compare. The result of this operator is equal to either 1, 0, or -1. It's equal to 1 if the first operand is greater than the second, zero if they are equal, and -1 if the second is greater than the first.	$comparison = $a <==> 123;
String Comparison
lt	less than	$before = $name lt "b";
le	less than or equal	$a_name = $name le "a";
gt	greater than	$after = $name gt "Tester";
ge	greater than or equal	$after_P = $name ge "O";
eq	equivalent to	$is_Bob = $name eq "Bob";
ne	not equal to	$not_Bob = $name ne "Bob";
cmp	The string comparison operator evaluates to either 1, 0, or -1.	$comparison = $name cmp "Bob";

Bash comparison
Refer to http://www.vectorsite.net/tsshell.html

[ "$shvar" = "fox" ]     String comparison, true if match.
   [ "$shvar" != "fox" ]    String comparison, true if no match.
   [ "$shvar" = "" ]        True if null variable.
   [ "$shvar" != "" ]       True if not null variable.

   [ "$nval" -eq 0 ]        Integer test; true if equal to 0.
   [ "$nval" -ge 0 ]        Integer test; true if greater than or equal to 0.
   [ "$nval" -gt 0 ]        Integer test; true if greater than 0.
   [ "$nval" -le 0 ]        Integer test; true if less than or equal to 0.
   [ "$nval" -lt 0 ]        Integer test; true if less than to 0.
   [ "$nval" -ne 0 ]        Integer test; true if not equal to 0.

   [ -d tmp ]               True if "tmp" is a directory.
   [ -f tmp ]               True if "tmp" is an ordinary file.
   [ -r tmp ]               True if "tmp" can be read.
   [ -s tmp ]               True if "tmp" is nonzero length.
   [ -w tmp ]               True if "tmp" can be written.
   [ -x tmp ]               True if "tmp" is executable.