Shell Programming and Scripting

Hi friends,
Today I found one strange behaviour of the tr command.
I used the following command:

Code:

echo "NEE"|tr [A-Z] [a-z]

Sometimes it was giving "nee" as ouput . sometimes it was giving "NEE" as output.
Finally I used the below code:

Code:

echo "NEE"|tr "[A-Z]" "[a-z]"

... and it gave me the correct result at every hit. I just want to know the reason behind this strange behaviour. Is it a problem of my Shell ? I am working in ksh88 version. Please help.

I can't really speak to the inconsistent output using "[A-Z] [a-z]", however I can say that I have never seen that using this method to go from upper to lower...

Code:

echo "NEE"|tr [:upper:] [:lower:]

This should be a syntax error. You must have a funny O/S if it works at all.

The correct syntax is:

Code:

echo "NEE" | tr '[A-Z]' '[a-z]'

... or to paraphrase man tr

Code:

echo "NEE" | tr "[:upper:]" "[:lower:]"

... but I prefer single quotes to make it totally obvious that the parameters are for tr not Shell.

Code:

echo "NEE" | tr '[:upper:]' '[:lower:]'

Btw. I've seen some amazing anomolies if there are files with single character names in the current directory.

Hmm

man tr on my servers do not show the need for a single or double quote.

I am using RHEL 5.3 and have been using the "[:upper:] [:lower:]" notation for years without quoting them. In fact we have a handful of Solaris and even HP-UX servers and many of our common scripts use that notation.

What OS are you using?
What version?
What version of tr?

It would be good to remember that quoting is required on that OS/Version or more importantly that version of tr.

@neelmani
Please post what Operating System and version you are running and what Shell you use.
(Prediction: The O/S going to be something unusual).


@ddreggors
Linux syntax can be wildly and inconsistently different from unix syntax and from other Linux systems syntax.
The unquoted syntax posted by the O/P is a syntax error on HP-UX.
There are much too many many Scripts running on live systems which contain faulty tr commands.
Please post your syntax and context.

Unlike character classes, tr ranges are not delimited by square brackets. tr '[A-Z]' '[a-z]' is converting [ and ] into themselves, a silent, harmless error.

The unquoted version could trigger pathname expansion in the shell, but I don't know why it would give you a syntax error. Could you please elaborate? Is it a tr syntax error? A shell error?

I think the original problem is as you alluded, the result of the shell matching single letter pathnames against the unquoted [a-z] and [A-Z]. This could alter the arguments to tr in such a way that none of the letters in NEE match the first range and so are never converted.

I would suggest trying tr A-Z a-z (valid only in the c/posix locale).

Regards,
Alister

---------- Post updated at 06:02 PM ---------- Previous update was at 05:53 PM ----------

It's not tr that requires the quoting; it's the shell (any posix-like sh). [:upper:] and [:lower:] are valid pathname expansion operations in the shell, each matching a single character name. If there's a match, instead of tr seeing a character class it will see the single character name with which the shell replaced the original character class (which to the shell was a pattern for globbing). If there's no match (probably usually the case, which is why you haven't noticed a problem), the shell doesn't modify the pattern and tr is invoked as intended.

Not to put a fine point on it, but all of those scripts have a bug and should be quoted.

Regards,
Alister

Thanks alister, that is good to know. I have been using tr for years with that syntax and just never have seen any problems. It had always performed as expected. When you mention the shell globbing it makes a lot more sense. I guess as you said, I have just been lucky

Admittedly, I use tr less often than say grep, awk, or sed... but enough that this is valuable to know.