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bug#29421: bug in command "tr"
From: |
Assaf Gordon |
Subject: |
bug#29421: bug in command "tr" |
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 <address@hidden> 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