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yerk5@hotmail.com wrote:
[snip]
> go=`cat ~/flag`
> if [ $go == 1 ]
> then
> cp ~/flag ~/flag2
> fi
>
>
> If I run this script from the shell prompt, it works exactly as
> expected. However if I set crontab to run it while I'm not logged in,
> it doesnt work and I come back to email from cron saying:
>
> [: 0: unexpected operator
>
> What's going on here? TIA.

At a guess, cron uses a different shell than you do at the command prompt

Some shells have the '[' command built in, and some don't
The built-in version of '[' recognizes the == equality test
The command version (an alias of the 'test' binary) does not

When you run your script at the commandline, you probably get the builtin
version of [, which recognizes == as valid

When you run your script through cron, you probably get a different shell, which
defaults to the command version of [, which in turn does not recognize == as valid

Try prepending a hashbang to your script, pointing it at the proper shell
interpreter. Something like...

#!/bin/bash
go=`cat ~/flag`
if [ $go == 1 ]
then
cp ~/flag ~/flag2
fi

- --
Lew Pitcher
IT Specialist, Enterprise Data Systems,
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed are my own, not my employers')
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Sweet. Worked like a charm. I suspected it was something along those
lines, but you crystalized it for me. It's fun to learn. Thanks again!

Lew Pitcher wrote:
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>
> yerk5@hotmail.com wrote:
> [snip]
> > go=`cat ~/flag`
> > if [ $go == 1 ]
> > then
> > cp ~/flag ~/flag2
> > fi
> >
> >
> > If I run this script from the shell prompt, it works exactly as
> > expected. However if I set crontab to run it while I'm not logged in,
> > it doesnt work and I come back to email from cron saying:
> >
> > [: 0: unexpected operator
> >
> > What's going on here? TIA.
>
> At a guess, cron uses a different shell than you do at the command prompt
>
> Some shells have the '[' command built in, and some don't
> The built-in version of '[' recognizes the == equality test
> The command version (an alias of the 'test' binary) does not
>
> When you run your script at the commandline, you probably get the builtin
> version of [, which recognizes == as valid
>
> When you run your script through cron, you probably get a different shell, which
> defaults to the command version of [, which in turn does not recognize == as valid
>
> Try prepending a hashbang to your script, pointing it at the proper shell
> interpreter. Something like...
>
> #!/bin/bash
> go=`cat ~/flag`
> if [ $go == 1 ]
> then
> cp ~/flag ~/flag2
> fi
>
> - --
> Lew Pitcher
> IT Specialist, Enterprise Data Systems,
> Enterprise Technology Solutions, TD Bank Financial Group
>
> (Opinions expressed are my own, not my employers')
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> zAFPpJRU1XqYJ8M/BkHpJz4=
> =gSJQ
> -----END PGP SIGNATURE-----

On 2005-11-14, Lew Pitcher wrote:
>
> yerk5@hotmail.com wrote:
> [snip]
>> go=`cat ~/flag`

Useless Use of Cat:

read go < ~/flag

>> if [ $go == 1 ]

There is no good reason to use == instead of -.

if [ "$go" = 1 ]

>> then
>> cp ~/flag ~/flag2
>> fi
>>
>>
>> If I run this script from the shell prompt, it works exactly as
>> expected. However if I set crontab to run it while I'm not logged in,
>> it doesnt work and I come back to email from cron saying:
>>
>> [: 0: unexpected operator
>>
>> What's going on here? TIA.
>
> At a guess, cron uses a different shell than you do at the command prompt
>
> Some shells have the '[' command built in, and some don't

All shells since 198?, if not since 197[7-9], have [ builtin.

> The built-in version of '[' recognizes the == equality test

In most shells it does not. The equality test is =, not ==.

> The command version (an alias of the 'test' binary) does not

True.

> When you run your script at the commandline, you probably get the builtin
> version of [, which recognizes == as valid

Pure serendipity.

> When you run your script through cron, you probably get a different shell, which
> defaults to the command version of [, which in turn does not recognize == as valid

It may use the built-in version of [, which also may not recognize ==.

> Try prepending a hashbang to your script, pointing it at the proper shell
> interpreter. Something like...
>
> #!/bin/bash

Better still, use the portable syntax, with a single =

> go=`cat ~/flag`

See above.

> if [ $go == 1 ]

if [ $go = 1 ]

... which works everywhere.

> then
> cp ~/flag ~/flag2
> fi


--
Chris F.A. Johnson, author |
Shell Scripting Recipes: | My code in this post, if any,
A Problem-Solution Approach | is released under the
2005, Apress | GNU General Public Licence

Chris F.A. Johnson wrote:

> > Some shells have the '[' command built in, and some don't
>
> All shells since 198?, if not since 197[7-9], have [ builtin.

(only early traditional shells miss it: it was added in System III, '81.
So nowadays it's only relevant in Ultrix' /bin/sh (but not /bin/sh5)
and bourne shells from socalled "bsd universes" on some unix variants)

2005-11-15, 21:58(+01), Sven Mascheck:
> Chris F.A. Johnson wrote:
>
>> > Some shells have the '[' command built in, and some don't
>>
>> All shells since 198?, if not since 197[7-9], have [ builtin.
>
> (only early traditional shells miss it: it was added in System III, '81.
> So nowadays it's only relevant in Ultrix' /bin/sh (but not /bin/sh5)
> and bourne shells from socalled "bsd universes" on some unix variants)

Yes, but there are occurences where it is the "[" binary command
that is used.

Mainly, when an utility is called by another command via the
"execle" system call, rather than via the system(3) function.

Like in:

env -i [ a = b ]
find . -exec [ -f {} ] \; -print

and so on (poor examples, I conceed).

Another good reason to stick to a standard syntax.

--
Stéphane

Stephane CHAZELAS wrote:

> but there are occurences where it is the "[" binary command that is used.

....if a "[" command is available at all. There's none on several unix
variants (e.g. Solaris, HP-UX, AIX), because it originates from BSD.