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10 - Other Frequently asked questions with answers.
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Q: How can I play an .au file ?
A: The file suffix .au means it's an audio file, so you can either do
the same as for mp3's: mpg123 file.au
or you can (since .au files are raw audio): cat file.au > /dev/dsp
or: cat file.au > /dev/audio
Q: What exactly is bash ?
A: If you have read this tutorial you would know ... it's a shell type.
Q: I wanna make some sub-directory's to /usr/local/ but I'm to lazy to write
almost the same line over and over again, is there any easier way ?
A: Yes there is: mkdir /usr/local/{dir1,dir2,dir3}
Q: I have a dir with files like this: file.1 file.2 file.3 etc.
is there any way I can list say, file.3, file.4, file.6, file.9 only
without using grep ?
A: Yes there is: ls file*[3469]*
Q: I want to remove some files with wildcards included in the command
(rm -rf .??*), is there any way I can see what the command will remove
before I actually do the command ?
A: Yes there is: echo rm -rf .??*
Q: How can I remove file names that are/have special characters like a file
named: -!?* !!?
A: Do this: rm ./-!?* !!?
The ./ makes sure it will look in the current directory, and the
(back slashes) will make sure that the special characters special meaning
is over looked, so they are treated just like any other character.
Q: I accidently deleted something on my system, is there any way
of getting it back ?
A: Yes there is, read this file /usr/doc/HOWTO/mini/Ext2fs-Undeletion
(or /usr/doc/HOWTO/mini/Ext2fs-Undeletion.gz)
This is also good knowledge if someone *hacks* your system
and think they are safe just because they deleted the logs.
Or you can download a program called 'recover' from www.freshmeat.net
Q: How do I compile my kernel ?
A: Read this file: /usr/doc/HOWTO/Kernel-HOWTO
Q: Can I make a variable read-only so noone can change it ?
A: Yes you can: readonly variable_name
As say that I have a variable: $myvar
Then I would do: readonly myvar
And to display all the read-only variables just do: readonly
Q: How can I display all the set variables ?
A: With the command: set
To get the eviorment use this command: env
And to display the system variables, type a $ and press TAB.
Q: Something is wrong with a script, but I dont know what, how can I find out ?
A: by doing this: /bin/sh -x <scriptname>
+ means that the command was successful.
- means that the command was unsuccessful.
Q: I'm using hexedit and simlar commands alot, but I'm getting to lazy to
find out where all the binarys live, isn't there any faster way of
opening a binary or script that's in my $PATH then to locate, find or
something like that and then go from there ?
A: Well, I dont know how much faster it is, but you can always
do this: hexedit `which <file>`
Q: How can I list only the directorys in a directory without the files ?
A: Well, some distros has an alias "lsd", and it does: ls -d */
Q: How can I transfer a file if the computer doesn't have any FTP ?
A: If you wanna actually copy a file to a place that dont have ftp
or for some other reason you can't use ftp, there is 2 commands that can
do this: scp (secure copy - requiers ssh)
And: rcp (remote copy - requiers rlogin)
They work like this:
scp local.file user@host.domain.com:/remote/directory/
rcp local.file user@host.domain.com:/remote/directory/
Q: Is there any way I can view my processes so I can see the free stack,
father processes siblings and children etc. ?
A: Yes there is, press: Ctrl + Scroll-Lock
Q: Is there any way I can view the memory buffers etc. ?
A: Yes there is, press: Shift + Scroll-Lock
Q: Is there any way to get some info from the stack ?
A: Yes there is press: AltGr + Scroll-Lock
Q: My volume is really low when I play stuff, how can I change it ?
A: Use the program `aumix` it should be on most systems by default,
and it's pretty self explanatory.
Q: I think it's a pain pressing upp arrow until I reach the command I want
to use, that is to long to type again, is there any faster way ?
A: Yes, press Ctrl+R and type something that matches a previously used
command, and just press enter to execute it or Ctrl+C to cancel.
Q: Is there any console based mpeg movie players ?
A: Not that I know of, but if there is, I'd like to know myself.
Q: How can I take a screenshot without having to install Gimp or something
like that ?
A: Well, the easyest way of taking a screen shot in X is to do the
following command: import -window root foo.jpg
That will dump a screen shot as foo.jpg, in your current directory.
Q: How can I import variables from one script to another, like a config file ?
A: You can read all variables from a file by doing ". <file name>", say
that you have a file called myvars and you want to you those variables
in a script, then you add the line: . myvars
in the beginning of the script, after the #!/bin/bash line.
The . is actually a command, that reads and executes commands in a file,
which here works to imported the variables since they are executed
from within the script.
Q: I'm using `port sentry` as a firewall controll software, now my routing
table is over full, how can I take away all that's routed to 'localhost'
in one command or string ?
A: Well like this: for ips in `route | grep local | cut -c 1-14`; do route del -host $ips gw 127.0.0.1 2>/dev/null ; done
That should do the trick.
Q: If I'm in a directory full or rpm files and I wanna find out which rpm that
contain say the file vga.h, how would I do that ?
A: Well you can do this:
for foo in `ls -1 *.rpm`; do rpm -qlp $foo | grep vga.h 1>/dev/null 2>&1 && echo $foo; done
Q: Is there any place I can find out where all the ^ (Ctrl) characters mean ?
A: Yes, look in the ascii table below, it works like this:
M is the 13'th character in the alphabet, and in the ascii table
013 (dec) has the value CR which means Carriage Return.
this means that ^M (Ctrl+M) is the same as pressing the return button.
And ^A which is 001 (dec) is Start of Header, in other words take the
cursor to the beginning of the current line.
Q: How do I write stuff in hex code ?
A: Well, like this:
-------------------------------------------------------------------------------
ASCII codes
-------------------------------------------------------------------------------
ASCII Table (7-bit)
Decimal Octal Hex Binary Value
------- ----- --- ------ -----
000 000 000 00000000 NUL (Null char.)
001 001 001 00000001 SOH (Start of Header)
002 002 002 00000010 STX (Start of Text)
003 003 003 00000011 ETX (End of Text)
004 004 004 00000100 EOT (End of Transmission)
005 005 005 00000101 ENQ (Enquiry)
006 006 006 00000110 ACK (Acknowledgment)
007 007 007 00000111 BEL (Bell)
008 010 008 00001000 BS (Backspace)
009 011 009 00001001 HT (Horizontal Tab)
010 012 00A 00001010 LF (Line Feed)
011 013 00B 00001011 VT (Vertical Tab)
012 014 00C 00001100 FF (Form Feed)
013 015 00D 00001101 CR (Carriage Return)
014 016 00E 00001110 SO (Serial In)
015 017 00F 00001111 SI (Serial Out)
016 020 010 00010000 DLE (Data Link Escape)
017 021 011 00010001 DC1 (XON) (Device Control 1)
018 022 012 00010010 DC2 (Device Control 2)
019 023 013 00010011 DC3 (XOFF)(Device Control 3)
020 024 014 00010100 DC4 (Device Control 4)
021 025 015 00010101 NAK (Negative Acknowledgement)
022 026 016 00010110 SYN (Synchronous Idle)
023 027 017 00010111 ETB (End of Trans. Block)
024 030 018 00011000 CAN (Cancel)
025 031 019 00011001 EM
026 032 01A 00011010 SUB
027 033 01B 00011011 ESC (Escape)
028 034 01C 00011100 FS (File Separator)
029 035 01D 00011101 GS
030 036 01E 00011110 RS (Request to Send)
031 037 01F 00011111 US
032 040 020 00100000 SP (Space)
033 041 021 00100001 !
034 042 022 00100010 "
035 043 023 00100011 #
036 044 024 00100100 $
037 045 025 00100101 %
038 046 026 00100110 &
039 047 027 00100111 '
040 050 028 00101000 (
041 051 029 00101001 )
042 052 02A 00101010 *
043 053 02B 00101011 +
044 054 02C 00101100 ,
045 055 02D 00101101 -
046 056 02E 00101110 .
047 057 02F 00101111 /
048 060 030 00110000 0
049 061 031 00110001 1
050 062 032 00110010 2
051 063 033 00110011 3
052 064 034 00110100 4
053 065 035 00110101 5
054 066 036 00110110 6
055 067 037 00110111 7
056 070 038 00111000 8
057 071 039 00111001 9
058 072 03A 00111010 :
059 073 03B 00111011 ;
060 074 03C 00111100 <
061 075 03D 00111101 =
062 076 03E 00111110 >
063 077 03F 00111111 ?
064 100 040 01000000 @
065 101 041 01000001 A
066 102 042 01000010 B
067 103 043 01000011 C
068 104 044 01000100 D
069 105 045 01000101 E
070 106 046 01000110 F
071 107 047 01000111 G
072 110 048 01001000 H
073 111 049 01001001 I
074 112 04A 01001010 J
075 113 04B 01001011 K
076 114 04C 01001100 L
077 115 04D 01001101 M
078 116 04E 01001110 N
079 117 04F 01001111 O
080 120 050 01010000 P
081 121 051 01010001 Q
082 122 052 01010010 R
083 123 053 01010011 S
084 124 054 01010100 T
085 125 055 01010101 U
086 126 056 01010110 V
087 127 057 01011111 W
088 130 058 01011000 X
089 131 059 01011001 Y
090 132 05A 01011010 Z
091 133 05B 01011011 [
092 134 05C 01011100
093 135 05D 01011101 ]
094 136 05E 01011110 ^
095 137 05F 01011111 _
096 140 060 01100000 `
097 141 061 01100001 a
098 142 062 01100010 b
099 143 063 01100011 c
100 144 064 01100100 d
101 145 065 01100101 e
102 146 066 01100110 f
103 147 067 01100111 g
104 150 068 01101000 h
105 151 069 01101001 i
106 152 06A 01101010 j
107 153 06B 01101011 k
108 154 06C 01101100 l
109 155 06D 01101101 m
110 156 06E 01101110 n
111 157 06F 01101111 o
112 160 070 01110000 p
113 161 071 01110001 q
114 162 072 01110010 r
115 163 073 01110011 s
116 164 074 01110100 t
117 165 075 01110101 u
118 166 076 01110110 v
119 167 077 01110111 w
120 170 078 01111000 x
121 171 079 01111001 y
122 172 07A 01111010 z
123 173 07B 01111011 {
124 174 07C 01111100 |
125 175 07D 01111101 }
126 176 07E 01111110 ~
127 177 07F 01111111 DEL
-------------------------------------------------------------------------------
Say that you want to echo "Hi" with hex code, you do this:
echo -e "x048x069"
The x part is to let `echo -e` know that it's hexa decimal code.
You can even hide commands like that.
Here is a script example of hiding the `top` command in hex and execute it:
-------------------------------------------------------------------------------
#!/bin/bash
hexcode='x074x06Fx070'
`echo -e $hexcode`
-------------------------------------------------------------------------------
This will execute what echo echos, due to the "`"'s.
So that script will actually start the `top` command.
-------------------------------------------------------------------------------
Another question I got a while back is how to make a DWORD (Double Word),
that means how to rewrite an address or IP to hex/oct/dec.
And it's not that hard, all it takes is some mathematics.
It works like this:
There are several methods, but let's start with the Decimal way
of making a DWORD.
Say you have IP: 127.0.0.1
then you do:
127 * 16777216 = 2130706432
0 * 65536 = 0
0 * 256 = 0
1 * 1 = 1
Sum: 2130706433
Or if you have the IP: 123.123.123.123
123 * 16777216 = 2063597568
123 * 65536 = 8060928
123 * 256 = 31488
123 * 1 = 123
Sum: 2071690107
Note:
16777216 = 2^24
65536 = 2^16
256 = 2^8
1 = 2^0
Next method is to convert it to HEX, OCT etc, to convert from dec to oct etc.
you can either use the ascii table a few lines up, or you can download
a program called ascii from www.freshmeat.net.
Last time I saw it it was located at:
http://freshmeat.net/projects/ascii/download/ascii-3.0.tar.gz
So assuming you have downloaded that and and wanna covert 127.0.0.1 and
123.123.123.123 to HEX DWORDs, do this:
alien:~$ ascii 127 0 0 1
ASCII 7/15 is decimal 127, hex 7f, octal 177, bits 01111111: called ^?, DEL
Official name: Delete
ASCII 5/7 is decimal 087, hex 57, octal 127, bits 01010111: prints as `W'
Official name: Majuscule W
Other names: Capital W, Uppercase W
ASCII 3/0 is decimal 048, hex 30, octal 060, bits 00110000: prints as `0'
Official name: Digit Zero
ASCII 3/0 is decimal 048, hex 30, octal 060, bits 00110000: prints as `0'
Official name: Digit Zero
ASCII 3/1 is decimal 049, hex 31, octal 061, bits 00110001: prints as `1'
Official name: Digit One
alien:~$
Take the hex numbers after the decimal of 127, 0 and 1 and you'll come
to the conclution that 127.0.0.1 in a hex DWORD is: 7F303031
You can use OCT the same way .. with as many leading 0's as you please
0173.0173.0173.0173 or 000173.00000173.000173.000000000000000000000173,
it still means IP 123.123.123.123
And ofcorse to add on the confusion you can mix the methods.
0173.0x7b.00173.123
Now there is even more to this like that you can add any multiple of the
number 4294967296 (2^32) to the number without the IP changing ....
But let's not get into that ....
So basically typing:
http://0173.0x7b.00173.123/
in your web browser will end you up at IP 123.123.123.132 (which doesnt excist)
but the idea is the same for everything, so if you see some lame spammer
thinking that you wont know from what address he sent something ...
The just back count it and send abuse mail to his internet service provider.
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If someone has more questions mail, them to me at: alien@ktv.koping.se
maybe I'll include them in the tutorial, but I'll do my best to answer
the questions anyway.
Posted in