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Full Discussion: Passing a command in a variable
Top Forums UNIX for Dummies Questions & Answers Passing a command in a variable Post 302394073 by Corona688 on Wednesday 10th of February 2010 11:36:25 AM
Old 02-10-2010
---------- Post updated at 10:36 AM ---------- Previous update was at 10:26 AM ----------

[/COLOR]And I just realized one really brain-dead simple solution: Let the server do the parsing. I do this over ssh sometimes.

Code:
 vpass $account bash < commands

This also prevents people from inserting clever things in the 'commands' file that end up running locally.

[rest of the post]

Your method is a little naive in a couple ways. For one thing, it's a useless use of backticks:

Code:
# bad -- a Useless Use of Cat and Useless Use of Backticks in one.
# It not only makes an extra process and wastes memory,  but
# might prevent you reading all of a file >64KB since it won't
# fit in one shell variable.
for LINE in `cat file`
do
        ...
done

# better.  Reads one line at a time with no extra process at all.
# Works on files of any size.
while read LINE
do
        ...
done < file

Also, your xargs solution could be done with one fewer process like
Code:
xargs vpass < command

Basically, whenever you do 'cat foo' you can replace that with a shell redirection in nearly all circumstances. This is quite a bit more efficient.

As for why the command isn't doing what you expect, the shell doesn't substitue strings more than once -- it won't check inside things it substitutes for things like quoted strings or variables. So embedding strings and variables in a string won't work unless you explicitly tell the shell to re-evaluate it, with eval. Note that eval supports all valid syntax so someone could inject variables or local commands where you didn't expect them by escaping $ and so forth.
Code:
#!/bin/bash
STR="\"this is a string\""
STR2='$HOSTNAME'

function args
{
  echo "Has ${#} arguments"
}

# it LOOKS right...
echo $STR
# But it's being split into "\"this" "is" "a" "string"!
args $STR
# This also looks right...
eval echo $STR
# eval tells it to re-parse the line after substitution.
eval args $STR

# This will not substitute in variables.
echo $STR2
# This will!
eval echo "$STR2"

[COLOR="#738fbf"]
Last edited by Corona688; 02-10-2010 at 12:48 PM..
 

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LEARN ABOUT DEBIAN

grisbi

GRISBI(1)						      General Commands Manual							 GRISBI(1)

NAME

       grisbi - Personal finance tracking program based on GTK

SYNOPSIS

       grisbi [options] file...

DESCRIPTION

       This  manual  page  documents  briefly  the grisbi command.  This manual page was written for the Debian GNU/Linux distribution because the
       original program does not have a manual page.

       grisbi is a personal finance tracking program with a lot of features:
	* bank, cash and passive accounts
	* several accounts at the same time
	* several currencies, including euro
	* arbitrary currency for every operation
	* money interchange fees
	* switch to euro account per account
	* describe operations with relatives, categories, sub-categories, notes
	* transfers between accounts, even for accounts of different currencies
	* reconciled balances
	* automatic and manual expiries
	* automatic recall of last operation for every relatives
	* nice and easy user interface
	* online user manual
	* QIF import/export

OPTIONS

       These programs follow the usual GNU command line syntax, with long options starting with  two  dashes  (`-').   A  summary  of  options	is
       included below.

       -?, --help
	      Show summary of options.

       --version
	      Show version of program.

AUTHOR

       This manual page was written by Benjamin Drieu <benj@debian.org>, for the Debian GNU/Linux system (but may be used by others).

								  August 22, 2002							 GRISBI(1)
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