Revise the command so that all error messages are redirected to a file log txt

[{"Type":"MASTER","Line of Business":{"code":"LOB57","label":"Power"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SWG60","label":"IBM i"},"Platform":[{"code":"PF012","label":"IBM i"}],"Version":"6.1.0"}]

First thing to note is that there's couple of ways depending on your purpose and shell, therefore this requires slight understanding of multiple aspects. Additionally, certain commands such as time and strace write output to stderr by default, and may or may not provide a method of redirection specific to that command

Basic theory behind redirection is that a process spawned by shell (assuming it is an external command and not shell built-in) is created via fork() and

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

Shell redirections

Most typical, is via

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

 command [arg1] [arg2]  2> /dev/null

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

Let's come back to

 command [arg1] [arg2]  2> /dev/null

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

[n]redir-op word

For simple

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

some_function(){
    command1
    command2
} 2> my_log_file.txt

some_function(){
    command1
    command2
} 2> my_log_file.txt

The somewhat simplified syntax for typical command in shell would be

 command [arg1] [arg2]  2> /dev/null

The trick here is that redirection can appear anywhere. That is both

some_function(){
    command1
    command2
} 2> my_log_file.txt

some_function(){
    command1
    command2
} 2> my_log_file.txt

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

Note: The

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

some_function(){
    command1
    command2
} 2> my_log_file.txt

some_function(){
    command1
    command2
} 2> my_log_file.txt

If you may notice,

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

time echo foo 2>&1 > file.txt

#!/bin/sh
exec 2> ./my_log_file.txt
stat /etc/non_existing_file

In this example, the log file should show

time echo foo 2>&1 > file.txt

Yet another way is via functions. As kopciuszek noted in his answer, we can write function declaration with already attached redirection, that is

some_function(){
    command1
    command2
} 2> my_log_file.txt

Commands writing to stderr exclusively

Commands such as time and strace write their output to stderr by default. In case of time command, the only viable alternative is to redirect output of whole command , that is

time echo foo 2>&1 > file.txt

alternatively, synchronous list or subshell could be redirected if you want to separate the output ( as shown in related post ):

{ time sleep 1 2> sleep.stderr ; } 2> time.txt

Other commands, such as strace or

time echo foo 2>&1 > file.txt

time echo foo 2>&1 > file.txt

time echo foo 2>&1 > file.txt

{ time sleep 1 2> sleep.stderr ; } 2> time.txt

result=$(dialog --inputbox test 0 0 2>&1 1>/dev/tty);

but additionally, there is

{ time sleep 1 2> sleep.stderr ; } 2> time.txt

time echo foo 2>&1 > file.txt

How to redirect both the output and error of a command to a file?

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Which symbol redirects an error message to a file?