Shell Programming and Scripting

If the program returns success, it prints match. If it returns error, it prints mismatch. The rest is redirection to shunt all the unneeded output into /dev/null where it will go away and never be heard from again.

@agama

The "==" is not valid in standard unix "ksh" , and your example gives "Syntax error at line 4 : `==' is not expected.".

I have also checked Bourne Shell and Posix Shell. Still invalid.
However it might be valid in a Conditional Expression in ksh93 ?

The O/P is using "/bin/sh" which could be Bourne Shell or Posix Shell depending on what Operating System version we have here. We can deduce that it is not "bash" or "ksh". Safest to assume Bourne Shell


The rules:

Between single square brackets [...] the expression is evaluated according the the rules for "test" (or the shell emulation of "test").

Between double square brackets [[...]]the expression is evaluated according to the rules for Conditonal Expressions (a separate section of the "ksh" manual).

There is some overlap in the syntax for "test" and a "Conditional Expression" but in standard unix "ksh" none of them include "==".



On the subject of "diff". The "diff -q" syntax is not valid in standard unix. I think you'll find the equivalent "cmp -s" in most of versions.

This is developing into another classic thread where nobody has the same Operating System yet everybody assumes that unix/Linix commands are universal when they are not.

cmp would be more efficient.