I have this code
for p in "abra/cadabra reach/out"
do
r="$HOME/x/$p"
echo $r
done
But it only produces this:
/Users/terrencemonroebrannon/x/abra/cadabra reach/out
Not
/Users/terrencemonroebrannon/x/abra/cadabra /Users/terrencemonroebrannon/x/reach/out
as I would expect.
You have placed your two items in quotes, which bash interprets as a single token. That's what quotes are for. You would get the behavior you describe if you were to remove the quotes:
for p in abra/cadabra reach/out
do
r="$HOME/x/$p"
echo $r
done
Gives me:
/Users/lars/x/abra/cadabra
/Users/lars/x/reach/out
bash will see "abra/cadabra reach/out" as one token.
Quotes are not needed.
for p in abra/cadabra reach/out
do
r="$HOME/x/$p"
echo $r
done
Related
I have these variables:
bridge_xa_name_list=( "$br_int0_srxa" "$br_int1_srxa" "$br_int2_srxa" "$br_int6_srxa" "$br_int7_srxa" "$br_wan3_srxa1" "$br_wan3_srxa2" )
bridge_xb_name_list=( "$br_int0_srxb" "$br_int1_srxb" "$br_int2_srxb" "$br_int6_srxb" "$br_int7_srxb" "$br_wan3_srxb1" "$br_wan3_srxb2" )
I am trying to use a single loop to iterate all the elements for each array.
At the moment I have a functioning loop but only by referencing the $bridge_xa_name_list
for a in "${bridge_xa_name_list[#]}"; do
shell_echo_textval_green "Network Bridge Name Detected" "$a"
sleep 1
shell_echo_text "Verifying $a network State"
virsh_net_list=$(virsh net-list | grep active | grep $a)
if [[ ! $virsh_net_list == *"active" ]]
then
shell_echo "[Inactive]"
else
shell_echo "[Active]"
shell_echo_green "$a.xml found. Undefining anyway."
virsh net-undefine $a
fi
shell_echo_text "File $a.xml is at $srxa_fld_path"
if [[ -f ${srxa_fld_path}${a}.xml ]]
then
shell_echo "[Yes]"
else
shell_echo "[Not Found]"
shell_echo_text "Attempting to copy $a.xml template to ~/config/$srxa_nm"
cp $xml_file_path $srxa_fld_path${a}.xml
shell_echo ["Copied"]
#Check if Copy was sucessfull
if [[ -f $srxa_fld_path${a}.xml ]]
then
:
else
shell_echo_red "[Failed]"
shell_echo_red "There was an error when trying to copy ${a}.xml"
shell_echo_error_banner "Script Aborted! 1 error(s)"
exit 1
fi
done
$a in my script is iterating all the elements from the 1st array. However, I would like to include the second array as part of the same loop.
These are indexed arrays so you can iterate over the indexes:
for (( i = 0; i < ${#bridge_xa_name_list[#]}; i++ )); do
echo "${bridge_xa_name_list[i]}"
echo "${bridge_xb_name_list[i]}"
done
$a in my script is iterating all the elements from the 1st array. However, I would like to include the second array as part of the same loop.
I think you mean that you want to execute the loop body once for each element of bridge_xa_name_list and also once, separately, for each element of bridge_xb_name_list, without duplicating the body of the loop. Yes, there are at least two easy ways to do that:
Absolutely easiest would be to just specify the additional elements in the loop header:
for a in "${bridge_xa_name_list[#]}" "${bridge_xb_name_list[#]}"; do
# loop body ...
What you need to understand here is that the for loop syntax has nothing in particular to do with accessing an array. The in list of such a command designates zero or more individual values (shell "words") to iterate over, which in the case of your original code are produced by a parameter expansion involving array-valued parameter bridge_xa_name_list. But this is just a special case of the shell's general procedure of expanding each command (path expansion, parameter expansion, command expansion, etc.) before executing it. You can use that however you like.
OR
Make a function around the loop that executes it once for every function argument. Then call that function once for each array:
my_loop() {
for a in "$#"; do
# loop body
done
}
# ...
my_loop "${bridge_xa_name_list[#]}"
my_loop "${bridge_xb_name_list[#]}"
Note that this still exhibits the same expand-then-execute behavior described in the previous item, which is why you have to pass the expansion of each array (to one word per element). There is no direct way to pass the whole array as a single argument.
Note also that the shell supports a special shortcut for iterating over all the elements of $#. For that particular case, you can omit the in list altogether:
my_loop() {
for a; do
# loop body
done
}
Of course, you can also combine the above, by providing the function and calling it once with the elements of both arrays:
my_loop "${bridge_xa_name_list[#]}" "${bridge_xb_name_list[#]}"
I have a script with:
#!/bin/bash
mark=10+10
nb=2
echo $mark
echo $(($mark/$nb))
I don't understand why the second echo return 15.
It's because the precendence of operators, and because mark is not evaluated itself (in a math-sense of evaulation).
echo $(($mark/$nb)) is first replace to $((10+10/2)) which is then evaluated to 10+5 which is 5.
There are numerous solutions to the problem, e.g:
echo $((mark/nb)
echo $((($mark)/$nb))
Try this instead:
#!/bin/bash
mark=$((10+10))
nb=2
echo $mark
echo $(($mark/$nb))
The reason is that when assigning 10+10 no result is calculated. Instead 10+10/$nb is executed in the last line. And the result is 15 of course.
So I have an array like:
al_ap_version=('ap_version' '[[ $data -ne $version ]]')
And the condition gets evaluated inside a loop like:
for alert in alert_list; do
data=$(tail -1 somefile)
condition=$(eval echo \${$alert[1]})
if eval "$condition" ; then
echo SomeAlert
fi
done
Whilst this generally works with many scenarios, if $data returns something like "-/-" or "4.2.9", I get errors as it doesn't seem to like complex strings in the variable.
Obviously I can't enclose the variable in single quotes as it won't expand so I'm after any ideas to expand the $data variable (or indeed the $version var which suffers the same possible fate) in a way that the evaluation can handle?
Ignoring the fact that eval is probably super dangerous to use here (unless the data in somefile is controlled by you and only you), there are a few issues to fix in your example code.
In your for loop, alert_list needs to be $alert_list.
Also, as pointed out by #choroba, you should be using != instead of -ne since your input isn't always an integer.
Finally, while debugging, you can add set -x to the top of your script, or add -x to the end of your shebang line to enable verbose output (helps to determine how bash is expanding your variables).
This works for me:
#!/bin/bash -x
data=2.2
version=1
al_ap_version=('ap_version' '[[ $data != $version ]]')
alert_list='al_ap_version'
for alert in $alert_list; do
condition=$(eval echo \${$alert[1]})
if eval "$condition"; then
echo "alert"
fi
done
You could try a more functional approach, even though bash is only just barely capable of such things. On the whole, it is usually a lot easier to pack an action to be executed into a bash function and refer to it with the name of the function, than to try to maintain the action as a string to be evaluated.
But first, the use of an array of names of arrays is awkward. Let's get rid of it.
It's not clear to me the point of element 0, ap_version, in the array al_ap_version but I suppose it has something to do with error messages. If the order of alert processing isn't important, you could replace the list of names of arrays with a single associative array:
declare -A alert_list
alert_list[ap_version]=... # see below
alert_list[os_dsk]=...
and then process them with:
for alert_name in ${!alert_list[#]}; do
alert=${alert_list[$alert_name]}
...
done
Having done that, we can get rid of the eval, with its consequent ugly necessity for juggling quotes, by creating a bash function for each alert:
check_ap_version() {
(($version != $1))
}
Edit: It seems that $1 is not necessarily numeric, so it would be better to use a non-numeric comparison, although exact version match might not be what you're after either. So perhaps it would be better to use:
check_ap_version() {
[[ $version != $1 ]]
}
Note the convention that the first argument of the function is the data value.
Now we can insert the name of the function into the alert array, and call it indirectly in the loop:
declare -A alert_list
alert_list[ap_version]=check_ap_version
alert_list[os_dsk]=check_op_dsk
check_alerts() {
local alert_name alert
local data=$(tail -1 somefile)
for alert_name in ${!alert_list[#]}; do
alert=${alert_list[$alert_name]}
if $alert "$data"; then
signal_alert $alert_name
fi
done
}
If you're prepared to be more disciplined about the function names, you can avoid the associative array, and thereby process the alerts in order. Suppose, for example, that every function has the name check_<alert_name>. Then the above could be:
alert_list=(ap_version os_dsk)
check_alerts() {
local alert_name
local data=$(tail -1 somefile)
for alert_name in $alert_list[#]; do
if check_$alert_name "$data"; then
signal_alert $alert_name
fi
done
}
I needed to run a script over a bunch of files, which paths were assigned to train1, train2, ... , train20, and I thought 'why not make it automatic with a bash script?'.
So I did something like:
train1=path/to/first/file
train2=path/to/second/file
...
train20=path/to/third/file
for i in {1..20}
do
python something.py train$i
done
which didn't work because train$i echoes train1's name, but not its value.
So I tried unsuccessfully things like $(train$i) or ${train$i} or ${!train$i}.
Does anyone know how to catch the correct value of these variables?
Use an array.
Bash does have variable indirection, so you can say
for varname in train{1..20}
do
python something.py "${!varname}"
done
The ! introduces the indirection, so "get the value of the variable named by the value of varname"
But use an array. You can make the definition very readable:
trains=(
path/to/first/file
path/to/second/file
...
path/to/third/file
)
Note that this array's first index is at position zero, so:
for ((i=0; i<${#trains[#]}; i++)); do
echo "train $i is ${trains[$i]}"
done
or
for idx in "${!trains[#]}"; do
echo "train $idx is ${trains[$idx]}"
done
You can use array:
train[1]=path/to/first/file
train[2]=path/to/second/file
...
train[20]=path/to/third/file
for i in {1..20}
do
python something.py ${train[$i]}
done
Or eval, but it awfull way:
train1=path/to/first/file
train2=path/to/second/file
...
train20=path/to/third/file
for i in {1..20}
do
eval "python something.py $train$i"
done
Consider the following nonsense array:
# KIND[ID]=NAME
MONKEYS[1]="Oo Oo"
MONKEYS[2]="Aa Aa"
MONKEYS[3]="Ba Nana"
LIONS[5]="Mister Mufasa"
LIONS[7]="Cocoa Puff"
LIONS[8]="Lala Leo"
TIGERS[13]="Ben Gal"
TIGERS[15]="Tee Eye Double Guh Err"
TIGERS[22]="Oh Esex Diez Punto Cuatro"
With a given KIND and ID, I'm attempting to build a string that resembles $NAME[$ID] to get the associated name.
When explicitly stating an array name, the command behaves as expected echo "${LIONS[5]}"=>"Mister Mufasa"). However, whenever a variable is used, the shell responds with the given character in the string.
$LIONS[5] => 'e' # The fifth letter in "Mister Mufasa"
In other cases, I can't find a way to control interpolation to get the NAME
KIND="LIONS"
ID="5"
# Attempt to return value of `LIONS` when `KIND=LIONS`
echo $"${KIND}"; echo "\$${KIND}" #=> "$LIONS"
echo "$${KIND}" #=> "57800{KIND}" Interpolates "$$"
echo "\$\${KIND}"; "\$\${KIND}" #=> "$${KIND}"
I found the following works albeit "ugly"...
eval echo `echo \\$${KIND}`
However when introducing the ID things break once again:
eval echo `echo \\$${KIND}[$ID]`
#> title:5: no matches found: $LIONS[5]
#> no matches found: $LIONS[5]
I feel like I'm missing something very simple. I have a hunch I'm forgetting to escape something, but I'm not quite sure what.
Also, what "less redundant" alternatives to eval echo `echo... or eval echo `print... exist?
In bash, use indirect addressing:
REF="$KIND[$ID]" # Sets REF to "LIONS[5]"
echo "${!REF}" # Prints "Mister Mufasa"
EDIT: In zsh, use nested expansion instead:
echo "${(P)${KIND}[ID]}"