Having trouble updating my global variable in this shell script.
I have read that the variables inside the loops run on a sub shell. Can someone clarify how this works and what steps I should take.
USER_NonRecursiveSum=0.0
while [ $lineCount -le $(($USER_Num)) ]
do
thisTime="$STimeDuration.$NTimeDuration"
USER_NonRecursiveSum=`echo "$USER_NonRecursiveSum + $thisTime" | bc`
done
That particular style of loop does not run in a sub-shell, it will update the variable just fine. You can see that in the following code, equivalent to yours other than adding things that you haven't included in the question:
USER_NonRecursiveSum=0
((USER_Num = 4)) # Add this to set loop limit.
((lineCount = 1)) # Add this to set loop control variable initial value.
while [ $lineCount -le $(($USER_Num)) ]
do
thisTime="1.2" # Modify this to provide specific thing to add.
USER_NonRecursiveSum=`echo "$USER_NonRecursiveSum + $thisTime" | bc`
(( lineCount += 1)) # Add this to limit loop.
done
echo ${USER_NonRecursiveSum} # Add this so we can see the final value.
That loop runs four times and adds 1.2 each time to the value starting at zero, and you can see it ends up as 4.8 after the loop is done.
While the echo command does run in a sub-shell, that's not an issue as the backticks explicitly capture the output from it and "deliver" it to the current shell.
Related
Why is this make_request function ending just after a single traversal?
make_request(){
path="${1//' '/'%20'}"
echo $path
mkdir -p $HOME/"$1"
$(curl --output $HOME/"$1"/$FILE_NAME -v -X GET $BASE_URL"/"$API_METHOD"/"$path &> /dev/null)
# sample response from curl
# {
# "count":2,
# "items": [
# {"path": "somepath1", "type": "folder"},
# {"path": "somepath2", "type": "folder"},
# ]
# }
count=$(jq ".count" $HOME/"$1"/$FILE_NAME)
for (( c=0; c<$count; c++ ))
do
child=$(jq -r ".items[$c] .path" $HOME/"$1"/$FILE_NAME);
fileType=$(jq -r ".items[$c] .type" $HOME/"$1"/$FILE_NAME);
if [ "$fileType" == "folder" ]; then
make_request "$child"
fi
done
}
make_request "/"
make_request "/" should give the following output:
/folder
/folder/folder1-1
/folder/folder1-1/folder1-2
/folder/foler2-1
/folder/folder2-1/folder2-2
/folder/folder2-1/folder2-3 ...
but I am getting the following:
/folder
/folder/folder1-1
/folder/folder1-1/folder1-2
You are using global variables everywhere. Therefore, the inner call changes the loop variables c and count of the outer call, resulting in bogus.
Minimal example:
f() {
this_is_global=$1
echo "enter $1: $this_is_global"
((RANDOM%2)) && f "$(($1+1))"
echo "exit $1: $this_is_global"
}
Running f 1 prints something like
enter 1: 1
enter 2: 2
enter 3: 3
exit 3: 3
exit 2: 3
exit 1: 3
Solution: Make the variables local by writing local count=$(...) and so on. For your loop, you have to put an additional statement local c above the for.
As currently written all variables have global scope; this means that all function calls are overwriting and referencing the same set of variables, this in turn means that when a child function returns to the parent the parent will find its variables have been overwritten by the child, this in turn leads to the type of behavior seen here.
In this particular case the loop variable c leaves the last child process with a value of c=$count and all parent loops now see c=$count and thus exit; it actually gets a bit more interesting because count is also changing with each function call. The previous comment to add set -x (aka enable debug mode) before the first function call should show what's going on with each variable at each function call.
What OP wants to do is insure each function is working with a local copy of a variable. The easiest approach is to add a local <variable_list> at the top of the function, making sure to list all variables that should be treated as 'local', eg:
local path count c child fileType
change variables to have local scope instead of global.
...
local count; # <------ VARIABLE MADE LOCAL
count=$(jq ".count" $HOME/"$1"/$FILE_NAME)
local c; # <------ VARIABLE MADE LOCAL
for (( c=0; c<$count; c++ ))
do
....
done
...
I have these variables:
bridge_xa_name_list=( "$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[#]}" "${bridge_xb_name_list[#]}"
What I try to achieve, is to define global variables in my script. These variables can be reused in a loop (preferably a while loop..) and with every iteration, the loop should get a new set a variables.
My script (so far):
PACKAGE_ASSET_ID=AUTO`date +%s`000001
TITLE_ASSET_ID=AUTO`date +%s`000002
MOVIE_ASSET_ID=AUTO`date +%s`000003
PREVIEW_ASSET_ID=AUTO`date +%s`000004
POSTER_ASSET_ID=AUTO`date +%s`000005
while read name; do
#DATE=`date +%s`
#PACKAGE_ASSET_ID="AUTO${DATE}000001"
#TITLE_ASSET_ID="AUTO${DATE}000002"
#MOVIE_ASSET_ID="AUTO${DATE}000003"
#PREVIEW_ASSET_ID="AUTO${DATE}000004"
#POSTER_ASSET_ID="AUTO${DATE}000005"
echo $PACKAGE_ASSET_ID
echo $TITLE_ASSET_ID
echo $MOVIE_ASSET_ID
echo $PREVIEW_ASSET_ID
echo $POSTER_ASSET_ID
done <names.txt
Within the file names.txt, there are 15 entries. For every entry, the while loop needs to process these sets of variables. Giving me something like
AUTO1521884581000001
AUTO1521884581000002
AUTO1521884581000003
AUTO1521884581000004
AUTO1521884581000005
AUTO1521884592000001
AUTO1521884592000002
AUTO1521884592000003
AUTO1521884592000004
AUTO1521884592000005
As you can see in the script, I tried putting it into the while loop and with different syntax but regretfully, without success. The results I get are always the same set of variables, for all the 15 entries.
Did you really expect that bash (even bash!) would need more than a second to read one line?? Try adding the nanoseconds.
while read name; do
DATE=$(date +%s%N)
PACKAGE_ASSET_ID="AUTO${DATE}000001"
TITLE_ASSET_ID="AUTO${DATE}000002"
MOVIE_ASSET_ID="AUTO${DATE}000003"
PREVIEW_ASSET_ID="AUTO${DATE}000004"
POSTER_ASSET_ID="AUTO${DATE}000005"
echo $PACKAGE_ASSET_ID
echo $TITLE_ASSET_ID
echo $MOVIE_ASSET_ID
echo $PREVIEW_ASSET_ID
echo $POSTER_ASSET_ID
done <names.txt
Consider this PS1
PS1='\n${_:+$? }$ '
Here is the result of a few commands
$ [ 2 = 2 ]
0 $ [ 2 = 3 ]
1 $
1 $
The first line shows no status as expected, and the next two lines show the
correct exit code. However on line 3 only Enter was pressed, so I would like the
status to go away, like line 1. How can I do this?
Here's a funny, very simple possibility: it uses the \# escape sequence of PS1 together with parameter expansions (and the way Bash expands its prompt).
The escape sequence \# expands to the command number of the command to be executed. This is incremented each time a command has actually been executed. Try it:
$ PS1='\# $ '
2 $ echo hello
hello
3 $ # this is a comment
3 $
3 $ echo hello
hello
4 $
Now, each time a prompt is to be displayed, Bash first expands the escape sequences found in PS1, then (provided the shell option promptvars is set, which is the default), this string is expanded via parameter expansion, command substitution, arithmetic expansion, and quote removal.
The trick is then to have an array that will have the k-th field set (to the empty string) whenever the (k-1)-th command is executed. Then, using appropriate parameter expansions, we'll be able to detect when these fields are set and to display the return code of the previous command if the field isn't set. If you want to call this array __cmdnbary, just do:
PS1='\n${__cmdnbary[\#]-$? }${__cmdnbary[\#]=}\$ '
Look:
$ PS1='\n${__cmdnbary[\#]-$? }${__cmdnbary[\#]=}\$ '
0 $ [ 2 = 3 ]
1 $
$ # it seems that it works
$ echo "it works"
it works
0 $
To qualify for the shortest answer challenge:
PS1='\n${a[\#]-$? }${a[\#]=}$ '
that's 31 characters.
Don't use this, of course, as a is a too trivial name; also, \$ might be better than $.
Seems you don't like that the initial prompt is 0 $; you can very easily modify this by initializing the array __cmdnbary appropriately: you'll put this somewhere in your configuration file:
__cmdnbary=( '' '' ) # Initialize the field 1!
PS1='\n${__cmdnbary[\#]-$? }${__cmdnbary[\#]=}\$ '
Got some time to play around this weekend. Looking at my earlier answer (not-good) and other answers I think this may be probably the smallest answer.
Place these lines at the end of your ~/.bash_profile:
PS1='$_ret$ '
trapDbg() {
local c="$BASH_COMMAND"
[[ "$c" != "pc" ]] && export _cmd="$c"
}
pc() {
local r=$?
trap "" DEBUG
[[ -n "$_cmd" ]] && _ret="$r " || _ret=""
export _ret
export _cmd=
trap 'trapDbg' DEBUG
}
export PROMPT_COMMAND=pc
trap 'trapDbg' DEBUG
Then open a new terminal and note this desired behavior on BASH prompt:
$ uname
Darwin
0 $
$
$
$ date
Sun Dec 14 05:59:03 EST 2014
0 $
$
$ [ 1 = 2 ]
1 $
$
$ ls 123
ls: cannot access 123: No such file or directory
2 $
$
Explanation:
This is based on trap 'handler' DEBUG and PROMPT_COMMAND hooks.
PS1 is using a variable _ret i.e. PS1='$_ret$ '.
trap command runs only when a command is executed but PROMPT_COMMAND is run even when an empty enter is pressed.
trap command sets a variable _cmd to the actually executed command using BASH internal var BASH_COMMAND.
PROMPT_COMMAND hook sets _ret to "$? " if _cmd is non-empty otherwise sets _ret to "". Finally it resets _cmd var to empty state.
The variable HISTCMD is updated every time a new command is executed. Unfortunately, the value is masked during the execution of PROMPT_COMMAND (I suppose for reasons related to not having history messed up with things which happen in the prompt command). The workaround I came up with is kind of messy, but it seems to work in my limited testing.
# This only works if the prompt has a prefix
# which is displayed before the status code field.
# Fortunately, in this case, there is one.
# Maybe use a no-op prefix in the worst case (!)
PS1_base=$'\n'
# Functions for PROMPT_COMMAND
PS1_update_HISTCMD () {
# If HISTCONTROL contains "ignoredups" or "ignoreboth", this breaks.
# We should not change it programmatically
# (think principle of least astonishment etc)
# but we can always gripe.
case :$HISTCONTROL: in
*:ignoredups:* | *:ignoreboth:* )
echo "PS1_update_HISTCMD(): HISTCONTROL contains 'ignoredups' or 'ignoreboth'" >&2
echo "PS1_update_HISTCMD(): Warning: Please remove this setting." >&2 ;;
esac
# PS1_HISTCMD needs to contain the old value of PS1_HISTCMD2 (a copy of HISTCMD)
PS1_HISTCMD=${PS1_HISTCMD2:-$PS1_HISTCMD}
# PS1_HISTCMD2 needs to be unset for the next prompt to trigger properly
unset PS1_HISTCMD2
}
PROMPT_COMMAND=PS1_update_HISTCMD
# Finally, the actual prompt:
PS1='${PS1_base#foo${PS1_HISTCMD2:=${HISTCMD%$PS1_HISTCMD}}}${_:+${PS1_HISTCMD2:+$? }}$ '
The logic in the prompt is roughly as follows:
${PS1_base#foo...}
This displays the prefix. The stuff in #... is useful only for its side effects. We want to do some variable manipulation without having the values of the variables display, so we hide them in a string substitution. (This will display odd and possibly spectacular things if the value of PS1_base ever happens to begin with foo followed by the current command history index.)
${PS1_HISTCMD2:=...}
This assigns a value to PS1_HISTCMD2 (if it is unset, which we have made sure it is). The substitution would nominally also expand to the new value, but we have hidden it in a ${var#subst} as explained above.
${HISTCMD%$PS1_HISTCMD}
We assign either the value of HISTCMD (when a new entry in the command history is being made, i.e. we are executing a new command) or an empty string (when the command is empty) to PS1_HISTCMD2. This works by trimming off the value HISTCMD any match on PS1_HISTCMD (using the ${var%subst} suffix replacement syntax).
${_:+...}
This is from the question. It will expand to ... something if the value of $_ is set and nonempty (which it is when a command is being executed, but not e.g. if we are performing a variable assignment). The "something" should be the status code (and a space, for legibility) if PS1_HISTCMD2 is nonempty.
${PS1_HISTCMD2:+$? }
There.
'$ '
This is just the actual prompt suffix, as in the original question.
So the key parts are the variables PS1_HISTCMD which remembers the previous value of HISTCMD, and the variable PS1_HISTCMD2 which captures the value of HISTCMD so it can be accessed from within PROMPT_COMMAND, but needs to be unset in the PROMPT_COMMAND so that the ${PS1_HISTCMD2:=...} assignment will fire again the next time the prompt is displayed.
I fiddled for a bit with trying to hide the output from ${PS1_HISTCMD2:=...} but then realized that there is in fact something we want to display anyhow, so just piggyback on that. You can't have a completely empty PS1_base because the shell apparently notices, and does not even attempt to perform a substitution when there is no value; but perhaps you can come up with a dummy value (a no-op escape sequence, perhaps?) if you have nothing else you want to display. Or maybe this could be refactored to run with a suffix instead; but that is probably going to be trickier still.
In response to Anubhava's "smallest answer" challenge, here is the code without comments or error checking.
PS1_base=$'\n'
PS1_update_HISTCMD () { PS1_HISTCMD=${PS1_HISTCMD2:-$PS1_HISTCMD}; unset PS1_HISTCMD2; }
PROMPT_COMMAND=PS1_update_HISTCMD
PS1='${PS1_base#foo${PS1_HISTCMD2:=${HISTCMD%$PS1_HISTCMD}}}${_:+${PS1_HISTCMD2:+$? }}$ '
This is probably not the best way to do this, but it seems to be working
function pc {
foo=$_
fc -l > /tmp/new
if cmp -s /tmp/{new,old} || test -z "$foo"
then
PS1='\n$ '
else
PS1='\n$? $ '
fi
cp /tmp/{new,old}
}
PROMPT_COMMAND=pc
Result
$ [ 2 = 2 ]
0 $ [ 2 = 3 ]
1 $
$
I need to use great script bash-preexec.sh.
Although I don't like external dependencies, this was the only thing to help me avoid to have 1 in $? after just pressing enter without running any command.
This goes to your ~/.bashrc:
__prompt_command() {
local exit="$?"
PS1='\u#\h: \w \$ '
[ -n "$LASTCMD" -a "$exit" != "0" ] && PS1='['${red}$exit$clear"] $PS1"
}
PROMPT_COMMAND=__prompt_command
[-f ~/.bash-preexec.sh ] && . ~/.bash-preexec.sh
preexec() { LASTCMD="$1"; }
UPDATE: later I was able to find a solution without dependency on .bash-preexec.sh.
I am changing a bash script which has a structure as such:
#somewhere in the code
sim_counts=#... some value
function_name()
{
set $sim_counts
for hostname in $linux_hostnames; do
if [ $1 -eq 0 ]; then # if sim_counts equal 0
shift # jump forward in sim_counts
continue
fi
# ... more code
shift
done
}
Then it is called in the script:
function_name
I want to introduce a parameter to this function:
#somewhere in the code
sim_counts=#... some value
function_name()
{
ip=$1
set $sim_counts
for hostname in $linux_hostnames; do
if [ $1 -eq 0 ]; then # if sim_counts equal 0
shift # jump forward in sim_counts
continue
fi
# ... more code
shift
done
}
And call the function in following way:
function_name 10.255.192.123
What should I do to avoid $1 conflict of function parameter and the other value from set command ?
If I am correctly reading the set builtin page in the Bash Reference Manual, I believe the code as you have written it will just work. Quoting from that page:
The remaining N arguments are positional parameters and are assigned, in order, to $1, $2, … $N. The special parameter # is set to N.
In essence, any pre-existing values for the positional variables will be blown away. The first sentence on that manual page is also interesting:
This builtin is so complicated that it deserves its own section.
In short, I think your code should simply work as expected. You've saved the initial value of $1 (from the function call) into a temporary variable; as long as you refer to $ip for that specific value, you should be good. In my own test script, it seems that $1 gets blown away as I expect it should.