Subject: bug#29421: bug in command "tr"

From: Assaf Gordon <[email-masked]>
Date: Thu, 23 Nov 2017 19:34:51 -0700

tag 29421 notabug
close 29421
stop

Hello,

On Thu, Nov 23, 2017 at 6:01 PM, wangjian <[email-masked]> wrote:
> Hi there, I think this is a bug
>
> mkdir empty_foler
> cd empty_foler
> touch a
> echo "abc" | tr [:blank:] +  # you will get “+bc” as output, instead of “abc”
> touch b
> echo "abc" | tr [:blank:]  # you will get “bbc” as output, instead of “abc”

This is not a bug, simply incorrect usage of the parameters on the shell.
Your shell (e.g. bash) expands unquoted [:blank:] to match ANY
file with names matching a/b/l/n/k , and replaces them on the commandline
BEFORE executing 'tr'.
Only if no files match a/b/l/n/k, then the string '[:blank:]' is
passed on to tr as-is.

Observe the following (in an empty directory):

$ echo [:blank:]
[:blank:]

$ touch a
$ echo [:blank:]
a

$ touch b
$ echo [:blank:]
a b

As opposed to using quotes:

$ echo "[:blank:]"
[:blank:]

And so, once you created the files a and b,
the command you executed was equivalent to
    echo abc | tr a b
which indeed results in "bbc".

To avoid such issues, always quote the parameters to 'tr'.

regards,
 - assaf