Difference between return and exit in Bash functions

Question

What is the difference between the return and exit statement in Bash functions with respect to exit codes

User · Answer

Adding an actionable aspect to a few of the other answers:

Both can give exit codes - default or defined by the function, and the only 'default' is zero for success for both exit and return. Any status can have a custom number 0-255, including for success.

Return is used often for interactive scripts that run in the current shell, called with . script.sh for example, and just returns you to your calling shell. The return code is then accessible to the calling shell - $? gives you the defined return status. Exit in this case also closes your shell (including SSH connections, if that's how you're working).

Exit is necessary if the script is executable and called from another script or shell and runs in a subshell. The exit codes then are accessible to the calling shell - return would give an error in this case.

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First of all  return is a keyword and exit is a function  That said  here s a simplest of explanations  return It returns a value from a function  exit It exits out of or abandons the current shell

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I don t think anyone has really fully answered the question because they don t describe how the two are used  OK  I think we know that exit kills the script  wherever it is called and you can assign a status to it as well such as exit or exit 0  or exit 7 and so forth  This can be used to determine how the script was forced to stop if called by another script  etc  Enough on exit  return  when called  will return the value specified to indicate the function s behavior  usually a 1 or a 0  For example         bin bash     isdirectory           if   -d  quot  1 quot          then         return 0       else         return 1       fi     echo  quot you will not see anything after the return like this text quot         Check like this      if isdirectory  1  then echo  quot is directory quot   else echo  quot not a directory quot   fi  Or like this      isdirectory    echo  quot not a directory quot   In this example  the test can be used to indicate if the directory was found  Notice that anything after the return will not be executed in the function  0 is true  but false is 1 in the shell  different from other programming languages  For more information on functions  Returning Values from Bash Functions Note  The isdirectory function is for instructional purposes only  This should not be how you perform such an option in a real script

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return will cause the current function to go out of scope  while exit will cause the script to end at the point where it is called   Here is a sample program to help explain this      bin bash  retfunc         echo  this is retfunc        return 1    exitfunc         echo  this is exitfunc        exit 1    retfunc echo  We are still here  exitfunc echo  We will never see this    Output      test sh this is retfunc   We are still here this is exitfunc

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Remember  functions are internal to a script and normally return from whence they were called by using the return statement  Calling an external script is another matter entirely  and scripts usually terminate with an exit statement  The difference  quot between the return and exit statement in Bash functions with respect to exit codes quot  is very small   Both return a status  not values per se   A status of zero indicates success  while any other status  1 to 255  indicates a failure  The return statement will return to the script from where it was called  while the exit statement will end the entire script from wherever it is encountered  return 0    Returns to where the function was called      contains 0  success    return 1    Returns to where the function was called      contains 1  failure    exit 0    Exits the script completely      contains 0  success    exit 1    Exits the script completely      contains 1  failure    If your function simply ends without a return statement  the status of the last command executed is returned as the status code  and will be placed in      Remember  return and exit give back a status code from 0 to 255  available in      You cannot stuff anything else into a status code  e g   return  quot cat quot    it will not work   But  a script can pass back 255 different reasons for failure by using status codes  You can set variables contained in the calling script  or echo results in the function and use command substitution in the calling script  but the purpose of return and exit are to pass status codes  not values or computation results as one might expect in a programming language like C

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Sometimes  you run a script using   or source     a sh   If you include an exit in the a sh  it will not just terminate the script  but end your shell session   If you include a return in the a sh  it simply stops processing the script

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exit terminates the current process  with or without an exit code  consider this a system more than a program function  Note that when sourcing  exit will end the shell  However  when running  it will just exit the script   return from a function go back to the instruction after the call  with or without a return code  return is optional and it s implicit at the end of the function  return can only be used inside a function    I want to add that while being sourced  it s not easy to exit the script from within a function without killing the shell  I think  an example is better on a  test  script     bin bash function die       echo   1  Something terrible wrong happen          clean your trash    exit 1      -f  whatever       die  quot whatever is not available quot    Now we can proceed echo  quot continue quot   doing the following  user    test Whatever is not available user   test -and- the shell will close  user      test Whatever is not available  Only test will finish and the prompt will show  The solution is to enclose the potentially procedure in   and       bin bash function die       echo   1  Something terrible wrong happen          Clean your trash    exit 1        Added               -f  whatever       die  quot whatever is not available quot        Now we can proceed     echo  quot continue quot      Added  Now  in both cases only test will exit

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If you convert a Bash script into a function  you typically replace exit N with return N  The code that calls the function will treat the return value the same as it would an exit code from a subprocess  Using exit inside the function will force the entire script to end

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The OP s question   What is the difference between the return and exit statement in BASH functions with respect to exit codes  Firstly  some clarification is required   A  return exit  statement is not required to terminate execution of a  function shell    A  function shell  will terminate when it reaches the end of its code list  even with no  return exit  statement   A  return exit  statement is not required to pass a value back from a terminated  function shell    Every process has a built-in variable    which always has a numeric value   It is a special variable that cannot be set like  quot   1 quot   but it is set only in special ways  see below     The value of    after the last command to be executed in the  called function   sub shell  is the value that is passed back to the  function caller   parent shell    That is true whether the last command executed is   quot return  n  quot    quot exit  n  quot   or plain   quot return quot  or something else which happens to be the last command in the called function s code    In the above bullet list  choose from  quot  x y  quot  either always the first item or always the second item to get statements about functions and return  or shells and exit  respectively  What is clear is that they both share common usage of the special variable    to pass values upwards after they terminate    Now for the special ways that    can be set   When a called function terminates and returns to its caller then    in the caller will be equal to the final value of    in the terminated function  When a parent shell implicitly or explicitly waits on a single sub shell and is released by termination of that sub shell  then    in the parent shell will be equal to the final value of    in the terminated sub shell  Some built-in functions can modify    depending upon their result  But some don t  Built-in functions  quot return quot  and  quot exit quot   when followed by a numerical argument both    with argument  and terminate execution   It is worth noting that    can be assigned a value by calling exit in a sub shell  like this     exit 259    echo    3

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From man bash on return  n       Causes a function to stop executing and return  the value  specified by n to its caller   If n is omitted  the return status is that of the last  command executed  in  the function body        on exit  n       Cause  the  shell to exit with a status of n   If n is omitted  the exit status is  that  of  the  last command  executed    A  trap  on  EXIT  is executed before the shell terminates    EDIT   As per your edit of the question  regarding exit codes  return has nothing to do with exit codes  Exit codes are intended for applications scripts  not functions  So in this regard  the only keyword that sets the exit code of the script  the one that can be caught by the calling program using the    shell variable  is exit   EDIT 2   My last statement referring exit is causing some comments  It was made to differentiate return and exit for the understanding of the OP  and in fact  at any given point of a program shell script  exit is the only way of ending the script with an exit code to the calling process   Every command executed in the shell produces a local  exit code   it sets the    variable to that code  and can be used with if    amp  amp  and other operators to conditionally execute other commands   These exit codes  and the value of the    variable  are reset by each command execution   Incidentally  the exit code of the last command executed by the script is used as the exit code of the script itself as seen by the calling process    Finally  functions  when called  act as shell commands with respect to exit codes  The exit code of the function  within the function  is set by using return  So when in a function return 0 is run  the function execution terminates  giving an exit code of 0

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In simple words  mainly for newbie in coding   we can say       return   exits the function       exit     exits the program  called as process while running   Also if you observed  this is very basic  but          return   is the keyword      exit     is the function

[bash] Difference between return and exit in Bash functions

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