On Fri, May 16, 2008 at 02:07:10PM +0930, Ian Blackwell alleged:

Craig White wrote:

...

On my CentOS 4.6 server, this works...

if [ -z `grep entry_chooser.js /var/log/httpd/access_log` ]

On my CentOS 5.1 server, this gives me the following error...

./test_file.scr: line 3: [: too many arguments

Can anyone explain why the difference and suggest something that makes both cases happy?

Thanks

Craig

---

CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos

Not sure why 4.6 is allowing it, but your if test will be resolving to something like this:- if [ -z this line from your log file and another line and even more lines until your if test fails with too many arguments I hope you don't want me to keep typing to make the point ]

To fix it, wrap the grep instead double quotes as well as the ticks - e.g. if [ -z "`grep entry_chooser.js /var/log/httpd/access_log`" ] Then the output from the grep will be seen as one long string, not a multitude of words from your log file.

Even better is to use 'grep -q' to avoid possibly large string expansions... if grep -q entry_chooser.js /var/log/httpd/access_log ;then

On Fri, 2008-05-16 at 14:07 +0930, Ian Blackwell wrote:

Craig White wrote:

...

On my CentOS 4.6 server, this works...

if [ -z `grep entry_chooser.js /var/log/httpd/access_log` ]

On my CentOS 5.1 server, this gives me the following error...

./test_file.scr: line 3: [: too many arguments

Can anyone explain why the difference and suggest something that makes both cases happy?

Not sure why 4.6 is allowing it, but your if test will be resolving to something like this:- if [ -z this line from your log file and another line and even more lines until your if test fails with too many arguments I hope you don't want me to keep typing to make the point ]

To fix it, wrap the grep instead double quotes as well as the ticks - e.g. if [ -z "`grep entry_chooser.js /var/log/httpd/access_log`" ] Then the output from the grep will be seen as one long string, not a multitude of words from your log file.

---- That works fine one CentOS 5 (double quotes and backtics) but not on CentOS 4.6

Thanks...I guess it's good enough for now.

Craig

On Fri, 2008-05-16 at 17:03 +0930, Ian Blackwell wrote:

Craig White wrote:

...

That works fine one CentOS 5 (double quotes and backtics) but not on CentOS 4.6

Thanks...I guess it's good enough for now.

Craig

---

CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos

I can only imagine it is "working" in 4.6 because the result of "grep entry_chooser.js /var/log/httpd/access_log" is either empty or 1 "word". The test syntax [ -z xxx ] would report the "too many arguments" error whenever the grep returned more than one word. You can test this at your command line by typing in:- [ -z one ] and [ -z one two three four five ]

The first will return "false" but you'll just see another bash prompt, the second will report the "too many arguments" error. This is certainly the case for me using RHEL4.6, so I would imagine CentOS4.6 should be the same. You can also see it explained by these commands and results:- [irb@zaphod ~]$ [ -z ] [irb@zaphod ~]$ echo $? 0 [irb@zaphod ~]$ [ -z one ] [irb@zaphod ~]$ echo $? 1 [irb@zaphod ~]$[ -z one two three four ] -bash: [: too many arguments [irb@zaphod ~]$ echo $? 2 [irb@zaphod ~]$

I hope this helps you understand why it is "working" on one machine but not another.

Ian

PS: I always prefer $(cmd) to backtics for readability. e.g.

if [ -z "$(grep entry_chooser.js /var/log/httpd/access_log)" ]

PPS: grep -q works for me on RHEL4.6 and CentOS5.1

---- makes a lot of sense - thanks

Craig