I have a bash method that looks like this
function getServiceId() {
serviceId=$(docker -H $1 ps -qf label=com.docker.swarm.service.name=$2)
$3=serviceId
return 0
}
I execute this function like this
getServiceId $node1 $service1 retVal
The error comes from line $3=serviceId.
It tries to execute the the value of serviceId on bash thinking it is a bash command. My goal is to return the value in the variable serviceId.
How do I do that?
Simply capture the STDOUT of the getServiceId function.
function getServiceId() {
docker -H "$1" ps -qf "label=com.docker.swarm.service.name=$2"
}
serviceId="$(getServiceId "arg1" "arg2")"
echo "Service ID is $serviceId"
You don't return values from functions in shell; you write to standard output, or set global variables. (No one ever said shell promoted good software engineering practice.)
getServiceId () {
docker -H "$1" ps -qf label=com.docker.swarm.service.name="$2"
}
serviceID=$(getServiceID)
or
getServiceID () {
serviceID=$(docker -H "$1" ps -qf label=com.docker.swarm.service.name="$2")
}
Try this:
function getServiceId() {
local serviceId
read serviceId < <(
docker -H $1 ps -qf label=com.docker.swarm.service.name=$2
)
printf -v $3 "%s" "$serviceId"
}
getServiceId $node1 $service1 retVal
This will work fine for this specific case. But I like to use read for setting variable for a lot of thing like:
{ read foo ; read device total use free prct mpoint } < <(df -k /)
echo $use
or
# Work on DB
while IFS=$'\t' read id name label ;do
[ "$id" ] && (( id > 100 )) && {
# Doing something for entries with id > 100 ...
}
done < <(
sqlclient "SELECT id,name,label FROM ..."
)
But care: by default read will interpret backslashes \ as escape char (wiping a newline, for example). see help read:
read: read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...] Read a line from the standard input and split it into fields. Reads a single line from the standard input, or from file descriptor FD if the -u option is supplied. The line is split into fields as with word splitting, and the first word is assigned to the first NAME, the second word to the second NAME, and so on, with any leftover words assigned to the last NAME. Only the characters found in $IFS are recognized as word delimiters. If no NAMEs are supplied, the line read is stored in the REPLY variable. Options: -a array assign the words read to sequential indices of the array variable ARRAY, starting at zero -d delim continue until the first character of DELIM is read, rather than newline -e use Readline to obtain the line in an interactive shell -i text Use TEXT as the initial text for Readline -n nchars return after reading NCHARS characters rather than waiting for a newline, but honor a delimiter if fewer than NCHARS characters are read before the delimiter -N nchars return only after reading exactly NCHARS characters, unless EOF is encountered or read times out, ignoring any delimiter -p prompt output the string PROMPT without a trailing newline before attempting to read -r do not allow backslashes to escape any characters -s do not echo input coming from a terminal -t timeout time out and return failure if a complete line of input is not read within TIMEOUT seconds. The value of the TMOUT variable is the default timeout. TIMEOUT may be a fractional number. If TIMEOUT is 0, read returns immediately, without trying to read any data, returning success only if input is available on the specified file descriptor. The exit status is greater than 128 if the timeout is exceeded -u fd read from file descriptor FD instead of the standard input Exit Status: The return code is zero, unless end-of-file is encountered, read times out (in which case it's greater than 128), a variable assignment error occurs, or an invalid file descriptor is supplied as the argument to -u.
