Shell Programming and Scripting

Hi I am using -gt comparative operator in one of my shell script.

I have tested that in Linux platform but same code will go in many other platforms i.e.Somehow I do not have access to all the servers with these OS...



Can someone suggest that how to confirm that greater than operator will work in all the platforms.


Thanks, Ambar

The comparison will be shell specific, so the question we need to ask is 'What shell are you running on each platform?'

Can you also show us the area of code that is failing so we can suggest something more portable.


Thanks,
Robin

Sorry to correct you, but the behavior of "test" (/usr/bin/test) is standardized by POSIX and "-gt" can be expected to work in a certain way on every standard-conformant platform, regardless of the shell.

This (the aforementioned) is true for constructs like:

Code:

[ .... -gt .... ]

and

Code:

/usr/bin/test .... -gt ....

Shell-dependant is this:

Code:

[[ .... -gt .... ]]

because "[[" is a (shell-builtin) replacement for "[" and "test" and hence depending on the shell it is built into. Some shells (for incstance the ksh88 on AIX) implements "[" as a shell-builtin too, but if this is the case it should conform to the POSIX-standard, whereas the standard says nothing about "[[".

I hope this helps.

bakunin

[ .... -gt .... ] in /bin/sh runs on all Unix-like platforms in an identical way (compares integers and sets exit status).

To add: -gt also works in non-Posix shells, like Bourne shell and KSH88, any shell as long as it is Bourne-shell derived (so not csh or tcsh)..

[ ... ] or test is also a shell builtin utility in every implementation I know of posix compliant shells
[[ ... ]] is not a shell builtin utility, but are shell keywords (part of the shell syntax) (They are indeed not part of the POSIX specification, so only supported in certain shells (ksh, zsh, bash)).

Code:

$ type test \[ \[\[ \]\]
test is a shell builtin
[ is a shell builtin
[[ is a shell keyword
]] is a shell keyword