In bash, how to store a return value in a variable?
Solution 1:
Simplest answer:
the return code from a function can be only a value in the range from 0 to 255 . To store this value in a variable you have to do like in this example:
#!/bin/bash
function returnfunction {
# example value between 0-255 to be returned
return 23
}
# note that the value has to be stored immediately after the function call :
returnfunction
myreturnvalue=$?
echo "myreturnvalue is "$myreturnvalue
Solution 2:
The return value (aka exit code) is a value in the range 0 to 255 inclusive. It's used to indicate success or failure, not to return information. Any value outside this range will be wrapped.
To return information, like your number, use
echo "$value"
To print additional information that you don't want captured, use
echo "my irrelevant info" >&2
Finally, to capture it, use what you did:
result=$(password_formula)
In other words:
echo "enter: "
read input
password_formula()
{
length=${#input}
last_two=${input:length-2:length}
first=`echo $last_two| sed -e 's/\(.\)/\1 /g'|awk '{print $2}'`
second=`echo $last_two| sed -e 's/\(.\)/\1 /g'|awk '{print $1}'`
let sum=$first+$second
sum_len=${#sum}
echo $second >&2
echo $sum >&2
if [ $sum -gt 9 ]
then
sum=${sum:1}
fi
value=$second$sum$first
echo $value
}
result=$(password_formula)
echo "The value is $result"
Solution 3:
It is easy you need to echo the value you need to return and then capture it like below
demofunc(){
local variable="hellow"
echo $variable
}
val=$(demofunc)
echo $val
Solution 4:
Use the special bash variable "$?" like so:
function_output=$(my_function)
function_return_value=$?
Solution 5:
The answer above suggests changing the function to echo data rather than return it so that it can be captured.
For a function or program that you can't modify where the return value needs to be saved to a variable (like test
/[
, which returns a 0/1 success value), echo $?
within the command substitution:
# Test if we're remote.
isRemote="$(test -z "$REMOTE_ADDR"; echo $?)"
# Or:
isRemote="$([ -z "$REMOTE_ADDR" ]; echo $?)"
# Additionally you may want to reverse the 0 (success) / 1 (error) values
# for your own sanity, using arithmetic expansion:
remoteAddrIsEmpty="$([ -z "$REMOTE_ADDR" ]; echo $((1-$?)))"
E.g.
$ echo $REMOTE_ADDR
$ test -z "$REMOTE_ADDR"; echo $?
0
$ REMOTE_ADDR=127.0.0.1
$ test -z "$REMOTE_ADDR"; echo $?
1
$ retval="$(test -z "$REMOTE_ADDR"; echo $?)"; echo $retval
1
$ unset REMOTE_ADDR
$ retval="$(test -z "$REMOTE_ADDR"; echo $?)"; echo $retval
0
For a program which prints data but also has a return value to be saved, the return value would be captured separately from the output:
# Two different files, 1 and 2.
$ cat 1
1
$ cat 2
2
$ diffs="$(cmp 1 2)"
$ haveDiffs=$?
$ echo "Have differences? [$haveDiffs] Diffs: [$diffs]"
Have differences? [1] Diffs: [1 2 differ: char 1, line 1]
$ diffs="$(cmp 1 1)"
$ haveDiffs=$?
$ echo "Have differences? [$haveDiffs] Diffs: [$diffs]"
Have differences? [0] Diffs: []
# Or again, if you just want a success variable, reverse with arithmetic expansion:
$ cmp -s 1 2; filesAreIdentical=$((1-$?))
$ echo $filesAreIdentical
0