Linux classes [:keyword:]

Hi_This_is_Dev · 05-14-2009, 09:39 AM

Hi All,

The rm command removes all files whose names are in lower case:

Code:

[root@localhost ~]# touch abc
[root@localhost ~]# touch a


[root@localhost ~]# rm [[:lower:]]
rm: remove regular empty file `a'? y

however, as you can see that the file "abc" is not being prompted for removal.

So, the question is: How to make use of Linux classes that can work with strings, that is file/directory names consisting of more than one character?

Thanks in advance!

Dev.

dave.donaghy · 05-14-2009, 09:45 AM

A * indicates "one or more of the preceding character".

Since, in your example, the "preceding character" is a class consisting of any lower-case alphabetic character, you can use this:

# echo rm [[:lower:]]*

(I always find that the echo keeps things safe, especially when doing something dangerous, like rm with wildcards, until I'm sure it's correct.)

... and then this ...

# rm [[:lower:]]*

Hi_This_is_Dev · 05-15-2009, 06:47 AM

Hi Dave,

Thanks! It serves the purpose!

Here is my finding:

Code:

[root@localhost ~]# rm [[:lower:]]*
rm: remove regular empty file `a'? y
rm: remove regular file `anaconda-ks.cfg'? n
rm: remove regular empty file `d'? n
rm: remove regular file `data'? 
[root@localhost ~]#

Quote:

Originally Posted by dave.donaghy

A * indicates "one or more of the preceding character".

Since, in your example, the "preceding character" is a class consisting of any lower-case alphabetic character, you can use this:

# echo rm [[:lower:]]*

(I always find that the echo keeps things safe, especially when doing something dangerous, like rm with wildcards, until I'm sure it's correct.)

... and then this ...

# rm [[:lower:]]*

Hi_This_is_Dev · 05-15-2009, 07:02 AM

Now here is another scenario:

1) Delete all files which have no extension names- do keep the ones which have them.

2) Delete all files which have extensions names- don't delete the ones which have them.

*Note: Using dot (.) in the criteria may not server the purpose in cases where a file name has multiple dots in it.

Example# 1:

Code:

[root@localhost ~]# ls
0    44   anaconda-ks.cfg  h                   PingReport
1    5    d                hi                  Ping Report for the Date of:
11   556  data             install.log         PingStatus.txt
2    56   Desktop          install.log.syslog  s
22   6    e                jj                  t
3    7    er               k                   work
333  8    f                logout-script.txt   z
4    9    g                names
[root@localhost ~]# rm *.*
rm: remove regular file `anaconda-ks.cfg'? n
rm: remove regular file `install.log'? n
rm: remove regular file `install.log.syslog'? n
rm: remove regular file `logout-script.txt'? n
rm: remove regular file `PingStatus.txt'? n
[root@localhost ~]#

Example# 2: This includes only those file names which begin with a dot (.)

Code:

[root@localhost ~]# echo rm .* | sort
rm . .. .abc.swp .bash_history .bash_logout .bash_profile .bashrc .cshrc .data.swp .dmrc .eggcups .esd_auth .gconf .gconfd .gnome .gnome2 .gnome2_private .gstreamer-0.10 .gtkrc-1.2-gnome2 .ICEauthority .lesshst .metacity .mozilla .nautilus .recently-used .recently-used.xbel .redhat .tcshrc .thumbnails .Trash .xsession-errors
[root@localhost ~]#

pixellany · 05-15-2009, 07:17 AM

Whenever you need to change the meaning of a character, the typical thing is to "escape" it with "\". The details depend on the context, but---in general---the use of "\" toggles the meaning of a character from whatever the default is in that situation. You can slog thru something like the Advanced Bash Scripting Guide---or you can simply experiment.

One example:

sed 's/./DOT/g' ##replaces all single characters with "DOT"

sed 's/\./DOT/g' ##replaces all literal "."s with "DOT"

(Obviously?) this only applies to characters which may have a special meaning in the context.....

jschiwal · 05-15-2009, 07:42 AM

FYI. In your first example, rm [[:lower:]]* will remove files that start with a lower case letter. The "*" in the shell globs "zero or more characters". It isn't used as in grep, sed or awk where it means "zero or more of the preceding character". You can however enable normal regular expressions with the "extglob" option.

Also, in another post, you were looking at hidden files. Be careful if you try to delete hidden files, because ".*" will also match ".." which is the parent directory.
Use ".[^.]*" instead.

There is another gotcha in the order of characters. The $LC_CTYPE locale variable can effect which characters match a regular expression.

Hi_This_is_Dev · 05-15-2009, 08:23 AM

Okay, pixellany and jschiwal. I will try that tomorrow because my tummy is aching so much because I have not taken any meals today. I must leave the lab now!