logging blocks of code to log files in bash - bash

Question

I have a huge bash script and I want to log specific blocks of code to a specific & small log files (instead of just one huge log file).
I have the following two methods:
# in this case, 'log' is a bash function
# Using code block & piping
{
# ... bash code ...
} | log "file name"
# Using Process Substitution
log "file name" < <(
# ... bash code ...
)
Both methods may interfere with the proper execution of the bash script, e.g. when assigning values to a variable (like the problem presented here).
How do you suggest to log the output of commands to log files?
Edit:
This is what I tried to do (besides many other variations), but doesn't work as expected:
function log()
{
if [ -z "$counter" ]; then
counter=1
echo "" >> "./General_Log_File" # Create the summary log file
else
(( ++counter ))
fi
echo "" > "./${counter}_log_file" # Create specific log file
# Display text-to-be-logged on screen & add it to the summary log file
# & write text-to-be-logged to it's corresponding log file
exec 1> >(tee "./${counter}_log_file" | tee -a "./General_Log_File") 2>&1
}
log # Logs the following code block
{
# ... Many bash commands ...
}
log # Logs the following code block
{
# ... Many bash commands ...
}
The results of executions varies: sometimes the log files are created and sometimes they don't (which raise an error).

Answer 1

You could try something like this:
function log()
{
local logfile=$1
local errfile=$2
exec > $logfile
exec 2> $errfile # if $errfile is not an empty string
}
log $fileA $errfileA
echo stuff
log $fileB $errfileB
echo more stuff
This would redirect all stdout/stderr from current process to a file without any subprocesses.
Edit: The below might be a good solution then, but not tested:
pipe=$(mktemp)
mknod $pipe p
exec 1>$pipe
function log()
{
if ! [[ -z "$teepid2" ]]; then
kill $teepid2
else
tee <$pipe general_log_file &
teepid1=$!
count=1
fi
tee <$pipe ${count}_logfile &
teepid2=$!
(( ++count ))
}
log
echo stuff
log
echo stuff2
if ! [[ -z "$teepid1" ]]; then kill $teepid1; fi

Answer 2

Thanks to Sahas, I managed to achieve the following solution:
function log()
{
[ -z "$counter" ] && counter=1 || (( ++counter ))
if [ -n "$teepid" ]; then
exec 1>&- 2>&- # close file descriptors to signal EOF to the `tee`
# command in the bg process
wait $teepid # wait for bg process to exit
fi
# Display text-to-be-logged on screen and
# write it to the summary log & to it's corresponding log file
( tee "${counter}.log" < "$pipe" | tee -a "Summary.log" 1>&4 ) &
teepid=$!
exec 1>"$pipe" 2>&1 # redirect stdout & stderr to the pipe
}
# Create temporary FIFO/pipe
pipe_dir=$(mktemp -d)
pipe="${pipe_dir}/cmds_output"
mkfifo "$pipe"
exec 4<&1 # save value of FD1 to FD4
log # Logs the following code block
{
# ... Many bash commands ...
}
log # Logs the following code block
{
# ... Many bash commands ...
}
if [ -n "$teepid" ]; then
exec 1>&- 2>&- # close file descriptors to signal EOF to the `tee`
# command in the bg process
wait $teepid # wait for bg process to exit
fi
It works - I tested it.
References:
Force bash script to use tee without piping from the command line # superuser.com - helped a lot
I/O Redirection # tldp.org
$! - PID Variable # tldp.org
TEST Operators: Binary Comparison # tldp.org

Answer 3

For simple redirection of bash code block, without using a dedicated function, do:
(
echo "log this block of code"
# commands ...
# ...
# ...
) &> output.log