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Full Discussion: Why I get bad bad substitution when using eval?
Top Forums Shell Programming and Scripting Why I get bad bad substitution when using eval? Post 302548675 by 915086731 on Friday 19th of August 2011 03:19:44 AM
Old 08-19-2011
Code:
[river@localhost ate]$ eval echo  \${map$i[1]}
0000
[river@localhost ate]$ a=`eval echo \\${map$i[2]}`
[river@localhost ate]$ echo $a                                       ??not "0000"??
0

The following result is right!
Code:
[river@localhost ate]$ a=$(eval echo \${map$i[1]})
[river@localhost ate]$ echo $a
0000
[river@localhost ate]$


Thanks!
I feel very puzzled, why I must need add '\' more, or add $(). Can you tell me ?
 

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LEARN ABOUT BSD

badsect

BADSECT(8)						      System Manager's Manual							BADSECT(8)

NAME

       badsect - create files to contain bad sectors

SYNOPSIS

       /sbin/badsect sector ...

DESCRIPTION

       Badsect makes a file to contain a bad sector.  Normally, bad sectors are made inaccessible by the standard formatter, which provides a for-
       warding table for bad sectors to the driver; see bad144(8) for details.	If a driver supports the bad blocking standard it is much  prefer-
       able  to  use  that  method to isolate bad blocks, since the bad block forwarding makes the pack appear perfect, and such packs can then be
       copied with dd(1).  The technique used by this program is also less general than bad block forwarding, as badsect can't make amends for bad
       blocks in the i-list of file systems or in swap areas.

       Adding  a  sector  which is suddenly bad to the bad sector table currently requires the running of the standard DEC formatter, as UNIX does
       not supply formatters.  Thus to deal with a newly bad block or on disks where the drivers do not support the bad-blocking standard  badsect
       may be used to good effect.

       Badsect	is used on a quiet file system in the following way: First mount the file system, and change to its root directory.  Make a direc-
       tory BAD there and change into it.  Run badsect giving as argument all the bad sectors you wish to add.	 (The  sector  numbers	should	be
       given  as  physical disk sectors relative to the beginning of the file system, exactly as the system reports the sector numbers in its con-
       sole error messages.)  Then change back to the root directory, unmount the file system and run fsck(8) on the file system.  The bad sectors
       should show up in two files or in the bad sector files and the free list.  Have fsck remove files containing the offending bad sectors, but
       do not have it remove the BAD/nnnnn files.  This will leave the bad sectors in only the BAD files.

       Badsect works by giving the specified sector numbers in a mknod(2) system call (after taking into account  the  filesystem's  block  size),
       creating a regular file whose first block address is the block containing bad sector and whose name is the bad sector number.  The file has
       0 length, but the check programs will still consider it to contain the block containing the sector.  This has the pleasant effect that  the
       sector is completely inaccessible to the containing file system since it is not available by accessing the file.

SEE ALSO

       mknod(2), bad144(8), fsck(8)

BUGS

       If  both  sectors which comprise a (1024 byte) disk block are bad, you should specify only one of them to badsect, as the blocks in the bad
       sector files actually cover both (bad) disk sectors.

       On the PDP-11, only sector number less than 131072 may be specified on 1024-byte block filesystems, 65536 on  512-byte  block  filesystems.
       This is because only a short int is passed to the system from mknod.

3rd Berkeley Distribution														BADSECT(8)
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