The bash shell process the command line by expanding variables and other "magic". After this is done, the line is now ready for processing by the command:
The eval simply executes the arguments as if those arguments had been the command itself. So bash executes:
Hi All,
I need to pass a variable to perl script from bash script, where in perl i am using if condition. Here is the cmd what i am using in perl
FROM_DATE="06/05/2008"
TO_DATE="07/05/2008"
"perl -ne ' print if ( $_ >="$FROM_DATE" && $_ <= "$TO_DATE" ) ' filename"
filename has... (10 Replies)
Hi,
I use AIX (ksh) and Linux (bash) servers. I'm trying to do scripts to will run in both ksh and bash, and most of the time it works. But this time I don't get it in bash (I'm more familar in ksh).
The goal of my script if to read a "config file" (like "ini" file), and make various report.... (2 Replies)
Just started BASH scripting, and I tried to make a script 'args' to display all of the arguments that I give to it.
#!/bin/bash
if
then
echo "No arguments specified."
fi
val=
for ((i=1; i <= $# ; i++))
do
eval "\$val=\$$i"
echo "Argument number $i is $var."
done
However... (3 Replies)
Hello all,
I have this shell script, but do not understand why the variables inside the if block does not keep its value outside. Is it because of the pipe ? How can i fix this problem ?
Thank you for helping.
local alarm=""
local num_alarm=0
local -a alarms
... (3 Replies)
Hi all,
I have a variable say var1 (output from somewhere, which I can't change)which store something like this:
echo $var1
name=fred
age=25
address="123 abc"
password=pass1234
how can I make the variable $name, $age, $address and $password contain the info?
I mean do this in a... (1 Reply)
Hello,
I am struggling with using variable made using "eval".
a=4
eval b$a=20
echo $b$a ???
As shown above, I am trying to call back the variable "bX" assuming I do not know the value of "a".
How can I do that?
I tried several combinations but nothing worked.
Thanks (10 Replies)
#aa=xxxx
#zz="cc $aa"
#aa=gggg
#echo $zz
out put is
cc xxxx
if I want to get
cc gggg
how should I do, I don't want to write zz="c $aa " after aa=gggg (2 Replies)
Hello,
Can I ask how to expand variable that contains another in bash? I need to loop variable within another one like this:
RD1=testgrp
RD2=testgroup
RD3=testgroupfile
RD4=tstgroup
...
RD40=try2013
DEST=/home/king/finaldir
for i in {1..40}; do
mv ${RD${i}} ${DEST}
done
I do not... (8 Replies)
In the below for loop, I extract a variable $d which is an id that will change each time. The bash executes the problem that I am having is that p (after the done) is the path with the extracted $d. However, I can not use it in subsequent loops as it is not reconized. I have been trying to change... (3 Replies)
Discussion started by: cmccabe
3 Replies
LEARN ABOUT PLAN9
source
exec(1) User Commands exec(1)NAME
exec, eval, source - shell built-in functions to execute other commands
SYNOPSIS
sh
exec [argument...]
eval [argument...]
csh
exec command
eval argument...
source [-h] name
ksh
*exec [arg...]
*eval [arg...]
DESCRIPTION
sh
The exec command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may
appear and, if no other arguments are given, cause the shell input/output to be modified.
The arguments to the eval built-in are read as input to the shell and the resulting command(s) executed.
csh
exec executes command in place of the current shell, which terminates.
eval reads its arguments as input to the shell and executes the resulting command(s). This is usually used to execute commands generated as
the result of command or variable substitution.
source reads commands from name. source commands may be nested, but if they are nested too deeply the shell may run out of file descrip-
tors. An error in a sourced file at any level terminates all nested source commands.
-h Place commands from the file name on the history list without executing them.
ksh
With the exec built-in, if arg is given, the command specified by the arguments is executed in place of this shell without creating a new
process. Input/output arguments may appear and affect the current process. If no arguments are given the effect of this command is to mod-
ify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking another program.
The arguments to eval are read as input to the shell and the resulting command(s) executed.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
EXIT STATUS
For ksh:
If command is not found, the exit status is 127. If command is found, but is not an executable utility, the exit status is 126. If a redi-
rection error occurs, the shell exits with a value in the range 1-125. Otherwise, exec returns a zero exit status.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), ksh(1), sh(1), attributes(5)SunOS 5.10 17 Jul 2002 exec(1)