[process] 127 Return code from $?

What is the meaning of return value 127 from $? in UNIX.

This error is also at times deceiving. It says file is not found even though the files is indeed present. It could be because of invalid unreadable special characters present in the files that could be caused by the editor you are using. This link might help you in such cases.

-bash: ./my_script: /bin/bash^M: bad interpreter: No such file or directory

The best way to find out if it is this issue is to simple place an echo statement in the entire file and verify if the same error is thrown.

A shell convention is that a successful executable should exit with the value 0. Anything else can be interpreted as a failure of some sort, on part of bash or the executable you that just ran. See also $PIPESTATUS and the EXIT STATUS section of the bash man page:

   For  the shell’s purposes, a command which exits with a zero exit status has succeeded.  An exit status
   of zero indicates success.  A non-zero exit status indicates failure.  When a command terminates  on  a
   fatal signal N, bash uses the value of 128+N as the exit status.

   If  a command is not found, the child process created to execute it returns a status of 127.  If a com-
   mand is found but is not executable, the return status is 126.

   If a command fails because of an error during expansion or redirection, the exit status is greater than
   zero.

   Shell  builtin  commands  return  a  status of 0 (true) if successful, and non-zero (false) if an error
   occurs while they execute.  All builtins return an exit status of 2 to indicate incorrect usage.

   Bash itself returns the exit status of the last command executed, unless  a  syntax  error  occurs,  in
   which case it exits with a non-zero value.  See also the exit builtin command below.

Generally it means:

127 - command not found

but it can also mean that the command is found,
but a library that is required by the command is NOT found.

If you're trying to run a program using a scripting language, you may need to include the full path of the scripting language and the file to execute. For example:

exec('/usr/local/bin/node /usr/local/lib/node_modules/uglifycss/uglifycss in.css > out.css');

It has no special meaning, other than that the last process to exit did so with an exit status of 127.

However, it is also used by bash (assuming you're using bash as a shell) to tell you that the command you tried to execute couldn't be executed (i.e. it couldn't be found). It's unfortunately not immediately deducible though, if the process exited with status 127, or if it couldn't found.

EDIT:
Not immediately deducible, except for the output on the console, but this is stack overflow, so I assume you're doing this in a script.

If the IBM mainframe JCL has some extra characters or numbers at the end of the name of unix script being called then it can throw such error.

127 - command not found

example: $caat The error message will

bash:

caat: command not found

now you check using echo $?