This is construction that is used if a shell in question does not know arrays. The way it is used in the script that you were handed, is a bit cumbersome. Instead of
this could be used:
eval works like this: first everything after eval is passed as parameter to eval. The shell processes the variable ${N}. The first $ is escaped ( \$ ), so that it is not treated as a special character. So after processing the command eval gets the following string (suppose N=1):
end then executes this. As a result you would get:
Last edited by Scrutinizer; 09-16-2010 at 06:32 PM..
I was checking my error logs today and ran into some errors I have not seen before maybe somebody has run into these before?
/etc/cron.quarter-hourly/owusers.sh:
Set effective gid to mail(12) failed!
/usr/local/mailwatch/check_sendmail_relay.sh: line 8:
thanks (1 Reply)
I am facing a strange error while creating posix threads:
Given below are two snippets of code, the first one works whereas the second one gives a garbage value in the output.
Snippet 1
This works:
--------------
int *threadids;
threadids = (int *) malloc (num_threads * sizeof(int));
... (4 Replies)
Hi All,
I'm writing a nagios check that will see if our ldap servers are in sync...
I got the status data into a nested array, I would like to search key of each array and if "OK" is NOT present, echo other key=>values in the current array to a variable
so...eg...let take the single array... (1 Reply)
I have an array and two variables as below,
I need to check if $datevar is present in $filename.
If so, i need to replace $filename with the values in the array.
I need the output inside an ARRAY
How can this be done.
Any help will be appreciated. Thanks in advance. (2 Replies)
Please help me out: I've seen this construct
awk '{...}1'several times, like in scrutinizer's today's post
awk '{for(i=2;i<=NF;i++)if($i==$1)$i=RS $i}1' infilebut I can't find (manuals, man pages, internet FAQs,...) an explanation of what it does resp. stands for. Any hint is appreciated! (5 Replies)
Hi!
Let's say I would like to convert "1", "2", "3" to "a", "b", "c" respectively. But if a record contains other number then return "X".
input:
1
2
3
4
output:
a
b
c
X
What is the syntax for:
if(array doesn't contain a particular index){
then print the value "X" instead} (12 Replies)
Trying to do some control flow parsing based on the index postion of an array member. Here is the pseudo code I am trying to write in (preferably in pure bash) where possible. I am thinking regex with do the trick, but need a little help.
pesudo code
if == ENDSINFIVEINTS ]]; then
do... (4 Replies)
hello,
i need a bit of help on how to do this effectively in bash without a lot of extra looping or massive switch/case
i have a long array of M elements and a short array of N elements, so M > N always. M is not a multiple of N.
for case 1, I want to stretch N to fit M
arrayHuge
H = (... (2 Replies)
Discussion started by: f77hack
2 Replies
LEARN ABOUT OSX
eval
eval(n) Tcl Built-In Commands eval(n)
__________________________________________________________________________________________________________________________________________________NAME
eval - Evaluate a Tcl script
SYNOPSIS
eval arg ?arg ...?
_________________________________________________________________DESCRIPTION
Eval takes one or more arguments, which together comprise a Tcl script containing one or more commands. Eval concatenates all its argu-
ments in the same fashion as the concat command, passes the concatenated string to the Tcl interpreter recursively, and returns the result
of that evaluation (or any error generated by it). Note that the list command quotes sequences of words in such a way that they are not
further expanded by the eval command.
EXAMPLES
Often, it is useful to store a fragment of a script in a variable and execute it later on with extra values appended. This technique is
used in a number of places throughout the Tcl core (e.g. in fcopy, lsort and trace command callbacks). This example shows how to do this
using core Tcl commands:
set script {
puts "logging now"
lappend $myCurrentLogVar
}
set myCurrentLogVar log1
# Set up a switch of logging variable part way through!
after 20000 set myCurrentLogVar log2
for {set i 0} {$i<10} {incr i} {
# Introduce a random delay
after [expr {int(5000 * rand())}]
update ;# Check for the asynch log switch
eval $script $i [clock clicks]
}
Note that in the most common case (where the script fragment is actually just a list of words forming a command prefix), it is better to |
use {*}$script when doing this sort of invocation pattern. It is less general than the eval command, and hence easier to make robust in |
practice. The following procedure acts in a way that is analogous to the lappend command, except it inserts the argument values at the
start of the list in the variable:
proc lprepend {varName args} {
upvar 1 $varName var
# Ensure that the variable exists and contains a list
lappend var
# Now we insert all the arguments in one go
set var [eval [list linsert $var 0] $args]
}
However, the last line would now normally be written without eval, like this: |
set var [linsert $var 0 {*}$args] |
SEE ALSO
catch(n), concat(n), error(n), interp(n), list(n), namespace(n), subst(n), tclvars(n), uplevel(n)
KEYWORDS
concatenate, evaluate, script
Tcl eval(n)