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Full Discussion: How to handle variable with special character?
Top Forums Shell Programming and Scripting How to handle variable with special character? Post 303026210 by bakunin on Wednesday 21st of November 2018 05:49:04 PM
Old 11-21-2018
Quote:
Originally Posted by green_k
the variable is "v$xyz",
No, it is not. A "variable" is something like "$name" or "${name}", where "name" is a name you choose. "$xyz" might be a variable, but "v$xyz" is a literal "v" followed by the content of a variable with the name "xyz".

Quote:
Originally Posted by green_k
the file name like v$xyz_xxxx_xxxx.txt.
OK, but is the "$xyz" in this filename now meant literally or should that signify the variable portion of the filename which you want to transport via the variable? If the first is the case a simple quotation will suffice, because this is what it is for - inside of (single) quotes the "$" loses its special meaning to the shell and reverts back to a normal character:

Code:
ls -l v$xyz_xxxx_xxxx.txt

will first replace "$xyz_xxxx_xxxx" with the content of a variable named "xyz_xxxx_xxxx" (which most probably will not exist so that it evaluates to "", the empty string) and therefore search for a file named "v.txt". Whereas:

Code:
ls -l 'v$xyz_xxxx_xxxx.txt'

(notice the single quotes) will look for a file named exactly this: "v$xyz_xxxx_xxxx.txt".

If "$xyz" is a variable and you want to use that as the changing part of an otherwise fixed filename then this code snippet is for you:

Code:
xyz="some$thing"
ls -l "v${xyz}_xxxx_xxxx.txt"

This will search for a file name "vsome$thing_xxxx_xxxx.txt". Because of the braces around "xyz" the shell knows that only this (and not the rest of the string) is the name of the variable. Notice the double quotes: you should habitually double-quote every use of any variable - ever and always! (There are only very few exceptions to this rule of thumb.) This way blanks (yes, filename can contain blanks) will not break your script.

I hope this helps.

bakunin
 

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LEARN ABOUT DEBIAN

rsockd

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

NAME

       rsockd - SOCKSified SOCKS server

SYNOPSIS

       rsockd [ -ver | -i | -I ]

DESCRIPTION

       rsockd  is the SOCKSified version of the SOCKS server sockd.  Functionally rsockd is identical to sockd except that it may (though not nec-
       essarily has to) make use of other SOCKS servers to reach some destinations. A number of rsockd's can be strung together or organized in  a
       cascade	or  other  more  complicated structures to serve the needs of a particular network configuration and restrictions.  Obviously this
       complicates the issues and make the setup and maintenance of the firewall more difficult. So use sockd instead whenever you can.

       This document only describes the features of rsockd that are different from sockd. You should read  sockd(5)  carefully	to  gain  a  basic
       understanding of of how the SOCKS server works.

       When  rsockd receives a request, it checks the request again its configuration (in exactly the same way that sockd does) to decider whether
       the request is to be accepted. The primary difference between sockd and rsockd is in how they establish connection to the destination  host
       of  a  accepted	request.  sockd  assumes that it can connect directly to the destination host and proceeds to do so.  rsockd makes no such
       assumption. Instead, it consults another configuration file to decide whether it can connect directly to the particular destination host or
       whether	it  has  to  use a proxy connection through another SOCKS server. In other words, it behaves just like a versatile SOCKS client in
       this regard. Therefore rsockd requires not only the SOCKS server configuration file /etc/sockd.fc or /etc/sockd.conf to decide  whether	to
       accept  or reject a request, but also the client configuration file /etc/socks.fc or /etc/socks.conf to decide how to reach the destination
       host.  If it is a multi-homed version and supports RBIND, it also needs the route file /etc/sockd.fr or /etc/sockd.fr to decide which  net-
       work interface to use for a connection.

       Look at it in a different way, you can think of sockd as a special case of rsockd, one which can connect directly to all destination hosts.
       In fact, an rsockd using the client configuration consisting of only this line

       direct	 ALL  0.0.0.0

       is functinally identical to the regular sockd.

       Anther thing to mention is related to the use of identd. Only the SOCKS server which the requesting host directly connects to can find  out
       the identity of the real user. Suppose user x on host C connects to rsockd on server B which in turn connects to sockd on server A in order
       to reach destination z. Host B can query identd on host C to find out whether the user is indeed x. To host A, the request appears to orig-
       inate  from user x on host B. An identd query from Host A to host B returns the userid that owns the rsockd process on host B, not the real
       user x.

OPTIONS

       See sockd(8).

EXAMPLES

       The follwoing is an example of the client configuration file. See related man pages for examples on server configuration and route files.

       # /etc/socks.conf for rsockd of domain rnd.xyz.com
       #
       # Use proxy connection through SOCKS server on socks.market.xyz.com
       # to reach hosts within market.xyz.com
       sockd	 @=socks.market.xyz.com  .market.xyz.com  0.0.0.0
       #
       # Use direct connect to all other hosts within xyz.com
       direct	 .xyz.com  0.0.0.0
       #
       # Use proxy connection through SOCKS server on gateway.xyz.com
       # to reach all others
       sockd	 @=gateway.xyz.com  ALL  0.0.0.0

FILES

       /etc/sockd.fc,  /etc/sockd.conf,  /etc/sockd.fr,  /etc/sockd.route,   /etc/socks.fc,   /etc/socks.conf,	 /etc/inetd.conf,   /etc/services,
       /var/adm/messages, /etc/syslog.conf

SEE ALSO

       sockd(8),    socks_clients(1),	sockd.conf(5),	 sockd.route(5),   socks.conf(5),   make_sockdfc(8),   make_sockdfr(8),   dump_sockdfc(8),
       dump_sockdfr(8)

AUTHOR

       Ying-Da Lee, ylee@syl.dl.nec.com

								    May 6, 1996 							 RSOCKD(8)
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