Redirecting output from a function block to a file in Linux - linux

Question

Just like we redirect output from a for loop block to a file
for ()
do
//do something
//print logs
done >> output file
Similarly in shell script, is there a way to redirect output from a function block to a file, something like this?
function initialize {
//do something
//print something
} >> output file
//call initialize
If not, is there some other way I can achieve that? Please note my function has lot of messages to be printed in a log. Redirecting output to a file at every line would result in a lot of I/O utilization.

Answer 1

Do the redirection when you are calling the function.
#!/bin/bash
initialize() {
echo 'initializing'
...
}
#call the function with the redirection you want
initialize >> your_file.log
Alternatively, open a subshell in the function and redirect the subshell output:
#!/bin/bash
initialize() {
( # opening the subshell
echo 'initializing'
...
# closing and redirecting the subshell
) >> your_file.log
}
# call the function normally
initialize

Answer 2

The way you suggest is actually perfectly valid. The Bash manual gives the function declaration syntax as follows (emphasis mine)1:
Functions are declared using this syntax:
name () compound-command [ redirections ]
or
function name [()] compound-command [ redirections ]
So this would be perfectly valid and replace the contents of outfile with the argument to myfunc:
myfunc() {
printf '%s\n' "$1"
} > outfile
Or, to append to outfile:
myappendfunc() {
printf '%s\n' "$1"
} >> outfile
However, even though you can put the name of your target file into a variable and redirect to that, like this:
fname=outfile
myfunc() { printf '%s\n' "$1"; } > "$fname"
I think think it's much clearer to do the redirection where you call the function – just like recommended in other answers. I just wanted to point out that you can have the redirection as part of the function declaration.
1And this is not a bashism: the POSIX Shell spec also allows redirections in the function definition command.

Answer 3

You can use for exec for shell redirection not sure if it will work for functions
exec > output_file
function initialize {
...
}
initialize

Answer 4

My solution is wrap the function.
init_internal(){
echo "this is init_internal with params: $#"
echo "arg1 $1"
echo "arg2 $2"
}
init() {
local LOG_PATH=$1
echo "LOG at: $LOG_PATH"
init_internal "${#:2}" > ./$LOG_PATH 2>&1
}
init log.log a b c d
cat ./log.log
It outputs:
LOG at: log.log
this is init_internal with params: a b c d
arg1 a
arg2 b