From time to time, you may get filenames with nonprinting characters, spaces, and other garbage in them. This is usually the result of some mistake — but it's a pain nevertheless.
If you're using a version of ls
that uses -q by default (and
most do these days), the ls command gives you
some help; it converts all nonprinting characters to a question mark (?), giving you some idea that something funny is
there.[2] For example:
% ls
ab??cdThis shows that there are two nonprinting characters between ab and cd. To
delete (or rename) this file,
you can use a wildcard pattern like ab??cd.
Be careful: when I was new to Unix, I once accidentally generated a lot of
weird filenames. ls told me that they all
began with ????, so I naively typed rm ????*. That's when my troubles began. See
Section 14.3 for the rest of
the gruesome story. (I spent the next day and night trying to undo the
damage.) The moral is: it's always a good idea to use echo
to test filenames with wildcards in
them.
If you're using an ls that came from
System V Unix, you have a different set of
problems. System V's ls doesn't convert the
nonprinting characters to question marks. In fact, it doesn't do anything at all
— it just spits these weird characters at your terminal, which can respond in
any number of strange and hostile ways. Most of the nonprinting characters
have special meanings — ranging from "don't take any more input" to "clear the
screen." [If you don't have a System V ls,
but you want this behavior for some reason, try GNU ls with its -N option. —
JP]
To prevent this, or to see what's actually
there instead of just the question marks, use the -b
option.[3] This tells ls to print the octal
value of any nonprinting characters, preceeded by a backslash. For
example:
% ls -b
ab\013\014cdThis shows that the nonprinting characters have octal values 13 and 14, respectively. If you look up these values in an ASCII table, you will see that they correspond to CTRL-k and CTRL-l. If you think about what's happening — you'll realize that CTRL-l is a formfeed character, which tells many terminals to clear the screen. That's why the regular ls command behaved so strangely.
Once you know what you're dealing with, you can use a wildcard pattern to delete or rename the file.
— ML
[2] Even in lses that use it, the
-q option is the default only when ls's standard output is a terminal. If you
pipe the output or redirect it to a file, remember to add
-q.
[3] On systems that don't support ls -b, pipe the ls -q output through cat -v or od -c ( Section 12.4) to see what the nonprinting characters are.