Error handling in Bash

Question

What is your favorite method to handle errors in Bash   The best example of handling errors I have found on the web was written by William Shotts  Jr at http   www linuxcommand org    He suggests using the following function for error handling in Bash      bin bash    A slicker error handling routine    I put a variable in my scripts named PROGNAME which   holds the name of the program being run   You can get this   value from the first item on the command line   0      Reference  This was copied from  lt http   www linuxcommand org wss0150 php gt   PROGNAME   basename  0   function error exit        ----------------------------------------------------------------     Function for exit due to fatal program error         Accepts 1 argument              string containing descriptive error message     ----------------------------------------------------------------       echo    PROGNAME     1 - Unknown Error    1 gt  amp 2     exit 1      Example call of the error exit function   Note the inclusion   of the LINENO environment variable   It contains the current   line number   echo  Example of error with line number and message  error exit   LINENO  An error has occurred     Do you have a better error handling routine that you use in Bash scripts

User · Answer

Another consideration is the exit code to return. Just "1" is pretty standard, although there are a handful of reserved exit codes that bash itself uses, and that same page argues that user-defined codes should be in the range 64-113 to conform to C/C++ standards.

You might also consider the bit vector approach that mount uses for its exit codes:

 0  success
 1  incorrect invocation or permissions
 2  system error (out of memory, cannot fork, no more loop devices)
 4  internal mount bug or missing nfs support in mount
 8  user interrupt
16  problems writing or locking /etc/mtab
32  mount failure
64  some mount succeeded

OR-ing the codes together allows your script to signal multiple simultaneous errors.

User · Answer

I ve used  die             echo  1         kill        before  i think because  exit  was failing for me for some reason  The above defaults seem like a good idea  though

User · Answer

Not sure if this will be helpful to you  but I modified some of the suggested functions here in order to include the check for the error  exit code from prior command  within it  On each  check  I also pass as a parameter the  message  of what the error is for logging purposes      bin bash  error exit         if            0     then         log sh   1          exit 1     fi     Now to call it within the same script  or in another one if I use export -f error exit  I simply write the name of the function and pass a message as parameter  like this      bin bash  cd  home myuser afolder error exit  Unable to switch to folder   rm   error exit  Unable to delete all files    Using this I was able to create a really robust bash file for some automated process and it will stop in case of errors and notify me  log sh will do that

User · Answer

I ve used  die             echo  1         kill        before  i think because  exit  was failing for me for some reason  The above defaults seem like a good idea  though

User · Answer

Another consideration is the exit code to return. Just "1" is pretty standard, although there are a handful of reserved exit codes that bash itself uses, and that same page argues that user-defined codes should be in the range 64-113 to conform to C/C++ standards.

You might also consider the bit vector approach that mount uses for its exit codes:

 0  success
 1  incorrect invocation or permissions
 2  system error (out of memory, cannot fork, no more loop devices)
 4  internal mount bug or missing nfs support in mount
 8  user interrupt
16  problems writing or locking /etc/mtab
32  mount failure
64  some mount succeeded

OR-ing the codes together allows your script to signal multiple simultaneous errors.

User · Answer

That s a fine solution  I just wanted to add  set -e   as a rudimentary error mechanism  It will immediately stop your script if a simple command fails  I think this should have been the default behavior  since such errors almost always signify something unexpected  it is not really  sane  to keep executing the following commands

User · Answer

Using trap is not always an option  For example  if you re writing some kind of re-usable function that needs error handling and that can be called from any script  after sourcing the file with helper functions   that function cannot assume anything about exit time of the outer script  which makes using traps very difficult  Another disadvantage of using traps is bad composability  as you risk overwriting previous trap that might be set earlier up in the caller chain   There is a little trick that can be used to do proper error handling without traps  As you may already know from other answers  set -e doesn t work inside commands if you use    operator after them  even if you run them in a subshell  e g   this wouldn t work      bin sh    prints      -- gt  outer   -- gt  inner     so 1 sh  line 16  some failed command  command not found    lt -- inner    lt -- outer  set -e  outer       echo  -- gt  outer     inner           exit code        echo  -- gt  cleanup      return  exit code       echo   lt -- outer     inner       set -e   echo  -- gt  inner    some failed command   echo   lt -- inner     outer   But    operator is needed to prevent returning from the outer function before cleanup  The trick is to run the inner command in background  and then immediately wait for it  The wait builtin will return the exit code of the inner command  and now you re using    after wait  not the inner function  so set -e works properly inside the latter      bin sh    prints      -- gt  outer   -- gt  inner     so 2 sh  line 27  some failed command  command not found   -- gt  cleanup  set -e  outer       echo  -- gt  outer    inner  amp    wait             exit code        echo  -- gt  cleanup      return  exit code       echo   lt -- outer     inner       set -e   echo  -- gt  inner    some failed command   echo   lt -- inner     outer   Here is the generic function that builds upon this idea  It should work in all POSIX-compatible shells if you remove local keywords  i e  replace all local x y with just x y      CLEANUP cleanup cmd  run cmd  args          cmd  and  args     A command to run and its arguments       cleanup cmd  A command that is called after cmd has exited    and gets passed the same arguments as cmd  Additionally  the   following environment variables are available to that command      -  RUN CMD  contains the  cmd  that was passed to  run     -  RUN EXIT CODE  contains the exit code of the command      If  cleanup cmd  is set   run  will return the exit code of that   command  Otherwise  it will return the exit code of  cmd     run       local cmd   1   shift   local exit code 0    local e was set 1  if   is shell attribute set e  then     set -e     e was set 0   fi      cmd        amp     wait             exit code           if     e was set    0    amp  amp  is shell attribute set e  then     set  e   fi    if   -n   CLEANUP     then     RUN CMD   cmd  RUN EXIT CODE   exit code    CLEANUP           return      fi    return  exit code     is shell attribute set       attribute  like  x    case   -  in        1    return 0              return 1      esac     Example of usage      bin sh set -e    Source the file with the definition of  run   previous code snippet     Alternatively  you may paste that code directly here and comment the next line      utils sh   main       echo  -- gt  main        CLEANUP cleanup run inner        echo   lt -- main      inner       echo  -- gt  inner        sleep 0 5  if     1     fail     then     oh my god look at this   fi   echo   lt -- inner      cleanup       echo  -- gt  cleanup        echo      RUN CMD     RUN CMD     echo      RUN EXIT CODE    RUN EXIT CODE    sleep 0 3   echo   lt -- cleanup    return  RUN EXIT CODE    main        Running the example       so 3 fail  echo  exit code       -- gt  main  fail -- gt  inner  fail   so 3  line 15  oh my god look at this  command not found -- gt  cleanup  fail     RUN CMD    inner      RUN EXIT CODE   127  lt -- cleanup exit code  127      so 3 pass  echo  exit code       -- gt  main  pass -- gt  inner  pass  lt -- inner -- gt  cleanup  pass     RUN CMD    inner      RUN EXIT CODE   0  lt -- cleanup  lt -- main exit code  0   The only thing that you need to be aware of when using this method is that all modifications of Shell variables done from the command you pass to run will not propagate to the calling function  because the command runs in a subshell

User · Answer

This has served me well for a while now  It prints error or warning messages in red  one line per parameter  and allows an optional exit code     Custom errors EX UNKNOWN 1  warning           Output warning messages       Color the output red if it s an interactive terminal        param  1     Messages      test -t 1  amp  amp  tput setf 4      printf   s n        gt  amp 2      test -t 1  amp  amp  tput sgr0   Reset terminal     true    error           Output error messages with optional exit code        param  1     Messages        param  N  Exit code  optional       messages                 If the last parameter is a number  it s not part of the messages     last parameter    messages     -1       if      last parameter       0-9           then         exit code  last parameter         unset messages       messages     - 1        fi      warning    messages           exit   exit code - EX UNKNOWN

User · Answer

I ve used  die             echo  1         kill        before  i think because  exit  was failing for me for some reason  The above defaults seem like a good idea  though

User · Answer

That s a fine solution  I just wanted to add  set -e   as a rudimentary error mechanism  It will immediately stop your script if a simple command fails  I think this should have been the default behavior  since such errors almost always signify something unexpected  it is not really  sane  to keep executing the following commands

User · Answer

Use a trap   tempfiles     cleanup       rm -f    tempfiles        trap cleanup 0  error       local parent lineno   1    local message   2    local code    3 -1     if    -n   message       then     echo  Error on or near line   parent lineno     message   exiting with status   code     else     echo  Error on or near line   parent lineno   exiting with status   code     fi   exit    code     trap  error   LINENO   ERR      then  whenever you create a temporary file   temp foo    mktemp -t foobar XXXXXX   tempfiles      temp foo      and  temp foo will be deleted on exit  and the current line number will be printed   set -e will likewise give you exit-on-error behavior  though it comes with serious caveats and weakens code s predictability and portability    You can either let the trap call error for you  in which case it uses the default exit code of 1 and no message  or call it yourself and provide explicit values  for instance   error   LINENO   the foobar failed  2   will exit with status 2  and give an explicit message

User · Answer

I ve used  die             echo  1         kill        before  i think because  exit  was failing for me for some reason  The above defaults seem like a good idea  though

User · Answer

This trick is useful for missing commands or functions   The name of the missing function  or executable  will be passed in      function handle error       status        last call  1        127 is  command not found         status    127     amp  amp  return      echo  you tried to call  last call      return      Trap errors  trap  handle error       ERR

User · Answer

Not sure if this will be helpful to you  but I modified some of the suggested functions here in order to include the check for the error  exit code from prior command  within it  On each  check  I also pass as a parameter the  message  of what the error is for logging purposes      bin bash  error exit         if            0     then         log sh   1          exit 1     fi     Now to call it within the same script  or in another one if I use export -f error exit  I simply write the name of the function and pass a message as parameter  like this      bin bash  cd  home myuser afolder error exit  Unable to switch to folder   rm   error exit  Unable to delete all files    Using this I was able to create a really robust bash file for some automated process and it will stop in case of errors and notify me  log sh will do that

User · Answer

I prefer something really easy to call  So I use something that looks a little complicated  but is easy to use  I usually just copy-and-paste the code below into my scripts  An explanation follows the code    This function is used to cleanly exit any script  It does this displaying a   given error message  and exiting with an error code  function error exit       echo     echo          exit 1    Trap the killer signals so that we can exit with a good message  trap  error exit  Received signal SIGHUP   SIGHUP trap  error exit  Received signal SIGINT   SIGINT trap  error exit  Received signal SIGTERM   SIGTERM   Alias the function so that it will print a message with the following format   prog-name  line    message  We have to explicitly allow aliases  we do this because they make calling the  function much easier  see example   shopt -s expand aliases alias die  error exit  Error   0    echo      LINENO - 1           I usually put a call to the cleanup function in side the error exit function  but this varies from script to script so I left it out  The traps catch the common terminating signals and make sure everything gets cleaned up  The alias is what does the real magic  I like to check everything for failure  So in general I call programs in an  if    type statement  By subtracting 1 from the line number the alias will tell me where the failure occurred  It is also dead simple to call  and pretty much idiot proof  Below is an example  just replace  bin false with whatever you are going to call     This is an example useage  it will print out  Error prog-name   1   Who knew false is false  if    bin false   then     die  Who knew false is false   fi

User · Answer

I use the following trap code  it also allows errors to be traced through pipes and  time  commands     bin bash set -o pipefail    trace ERR through pipes set -o errtrace    trace ERR through  time command  and other functions function error         JOB   0                 job name     LASTLINE   1            line of error occurrence     LASTERR   2             error code     echo  ERROR in   JOB    line   LASTLINE  with exit code   LASTERR       exit 1   trap  error   LINENO        ERR

User · Answer

I prefer something really easy to call  So I use something that looks a little complicated  but is easy to use  I usually just copy-and-paste the code below into my scripts  An explanation follows the code    This function is used to cleanly exit any script  It does this displaying a   given error message  and exiting with an error code  function error exit       echo     echo          exit 1    Trap the killer signals so that we can exit with a good message  trap  error exit  Received signal SIGHUP   SIGHUP trap  error exit  Received signal SIGINT   SIGINT trap  error exit  Received signal SIGTERM   SIGTERM   Alias the function so that it will print a message with the following format   prog-name  line    message  We have to explicitly allow aliases  we do this because they make calling the  function much easier  see example   shopt -s expand aliases alias die  error exit  Error   0    echo      LINENO - 1           I usually put a call to the cleanup function in side the error exit function  but this varies from script to script so I left it out  The traps catch the common terminating signals and make sure everything gets cleaned up  The alias is what does the real magic  I like to check everything for failure  So in general I call programs in an  if    type statement  By subtracting 1 from the line number the alias will tell me where the failure occurred  It is also dead simple to call  and pretty much idiot proof  Below is an example  just replace  bin false with whatever you are going to call     This is an example useage  it will print out  Error prog-name   1   Who knew false is false  if    bin false   then     die  Who knew false is false   fi

User · Answer

Another consideration is the exit code to return. Just "1" is pretty standard, although there are a handful of reserved exit codes that bash itself uses, and that same page argues that user-defined codes should be in the range 64-113 to conform to C/C++ standards.

You might also consider the bit vector approach that mount uses for its exit codes:

 0  success
 1  incorrect invocation or permissions
 2  system error (out of memory, cannot fork, no more loop devices)
 4  internal mount bug or missing nfs support in mount
 8  user interrupt
16  problems writing or locking /etc/mtab
32  mount failure
64  some mount succeeded

OR-ing the codes together allows your script to signal multiple simultaneous errors.

User · Answer

This function has been serving me rather well recently   action            Test if the first parameter is non-zero       and return straight away if so     if test  1 -ne 0     then         return  1     fi        Discard the control parameter       and execute the rest     shift 1              local status           Test the exit status of the command run       and display an error message on failure     if test   status  -ne 0     then         echo Command          failed  gt  amp 2     fi      return   status      You call it by appending 0 or the last return value to the name of the command to run  so you can chain commands without having to check for error values   With this  this statement block   command1 param1 param2 param3    command2 param1 param2 param3    command3 param1 param2 param3    command4 param1 param2 param3    command5 param1 param2 param3    command6 param1 param2 param3      Becomes this   action 0 command1 param1 param2 param3    action    command2 param1 param2 param3    action    command3 param1 param2 param3    action    command4 param1 param2 param3    action    command5 param1 param2 param3    action    command6 param1 param2 param3      lt  lt  lt Error-handling code here gt  gt  gt    If any of the commands fail  the error code is simply passed to the end of the block   I find it useful when you don t want subsequent commands to execute if an earlier one failed  but you also don t want the script to exit straight away  for example  inside a loop

User · Answer

An equivalent alternative to  set -e  is  set -o errexit   It makes the meaning of the flag somewhat clearer than just  -e    Random addition  to temporarily disable the flag  and return to the default  of continuing execution regardless of exit codes   just use  set  e echo  commands run here returning non-zero exit codes will not cause the entire script to fail  echo  false returns 1 as an exit code  false set -e   This precludes proper error handling mentioned in other responses  but is quick  amp  effective  just like bash

User · Answer

Use a trap   tempfiles     cleanup       rm -f    tempfiles        trap cleanup 0  error       local parent lineno   1    local message   2    local code    3 -1     if    -n   message       then     echo  Error on or near line   parent lineno     message   exiting with status   code     else     echo  Error on or near line   parent lineno   exiting with status   code     fi   exit    code     trap  error   LINENO   ERR      then  whenever you create a temporary file   temp foo    mktemp -t foobar XXXXXX   tempfiles      temp foo      and  temp foo will be deleted on exit  and the current line number will be printed   set -e will likewise give you exit-on-error behavior  though it comes with serious caveats and weakens code s predictability and portability    You can either let the trap call error for you  in which case it uses the default exit code of 1 and no message  or call it yourself and provide explicit values  for instance   error   LINENO   the foobar failed  2   will exit with status 2  and give an explicit message

User · Answer

That s a fine solution  I just wanted to add  set -e   as a rudimentary error mechanism  It will immediately stop your script if a simple command fails  I think this should have been the default behavior  since such errors almost always signify something unexpected  it is not really  sane  to keep executing the following commands

User · Answer

Reading all the answers on this page inspired me a lot   So  here s my hint   file content  lib trap sh  lib name  trap  lib version 20121026  stderr log   dev shm stderr log       TO BE SOURCED ONLY ONCE                                                                              if test    g libs  lib name       then     return 0 else     if test    g libs        0  then         declare -A g libs     fi     g libs  lib name   lib version fi       MAIN CODE                                                                              set -o pipefail    trace ERR through pipes set -o errtrace    trace ERR through  time command  and other functions set -o nounset      set -u   exit the script if you try to use an uninitialised variable set -o errexit      set -e   exit the script if any statement returns a non-true return value  exec 2 gt   stderr log                                                                                 FUNCTION  EXIT HANDLER                                                                             function exit handler          local error code           test  error code    0  amp  amp  return               LOCAL VARIABLES        ------------------------------------------------------------------               local i 0     local regex        local mem         local error file        local error lineno        local error message  unknown       local lineno                  PRINT THE HEADER        ------------------------------------------------------------------             Color the output if it s an interactive terminal     test -t 1  amp  amp  tput bold  tput setf 4                                    red bold     echo -e   n    EXIT HANDLER  n                GETTING LAST ERROR OCCURRED                                                                                        Read last file from the error log       ------------------------------------------------------------------           if test -f   stderr log          then             stderr    tail -n 1   stderr log                rm   stderr log      fi              Managing the line to extract information        ------------------------------------------------------------------            if test -n   stderr          then                       Exploding stderr on               mem   IFS              local shrunk stderr    echo   stderr    sed  s        g                IFS                 local stderr parts    shrunk stderr               IFS   mem                 Storing information on the error             error file    stderr parts 0                error lineno    stderr parts 1                error message                 for    i   3  i  lt      stderr parts      i                      do                     error message   error message    stderr parts  i-1                   done                Removing last      colon character              error message    error message                     Trim             error message     echo   error message    sed -e  s     t        sed -e  s    t              fi              GETTING BACKTRACE                                                                                backtrace    backtrace 2                 MANAGING THE OUTPUT                                                                                local lineno        regex     a-z  1      0-9  1           if     error lineno     regex               The error line was found on the log            e g  type  ff  without quotes wherever            --------------------------------------------------------------         then             local row    BASH REMATCH 1                lineno    BASH REMATCH 2                 echo -e  FILE  t t  error file               echo -e    row     t t  lineno  n               echo -e  ERROR CODE  t  error code                            test -t 1  amp  amp  tput setf 6                                       white yellow             echo -e  ERROR MESSAGE  n error message            else             regex     error file       error file  s   s   error file  s   s   error file                 if       backtrace      regex                       The file was found on the log but not the error line                    could not reproduce this case so far                    ------------------------------------------------------                 then                     echo -e  FILE  t t error file                      echo -e  ROW  t tunknown n                       echo -e  ERROR CODE  t  error code                       test -t 1  amp  amp  tput setf 6                               white yellow                     echo -e  ERROR MESSAGE  n  stderr                      Neither the error line nor the error file was found on the log                    e g  type  cp ffd fdf  without quotes wherever                    ------------------------------------------------------                 else                                             The error file is the first on backtrace list                         Exploding backtrace on newlines                     mem  IFS                     IFS                                                                     Substring  I keep only the carriage return                        others needed only for tabbing purpose                      IFS   IFS 0 1                      local lines     backtrace                        IFS  mem                      error file                         if test -n    lines 1                            then                             array     lines 1                                  for    i 2  i lt    array      i                                      do                                     error file   error file   array  i                                done                                Trim                             error file     echo   error file    sed -e  s     t        sed -e  s    t                              fi                      echo -e  FILE  t t error file                      echo -e  ROW  t tunknown n                       echo -e  ERROR CODE  t  error code                       test -t 1  amp  amp  tput setf 6                               white yellow                     if test -n    stderr                           then                             echo -e  ERROR MESSAGE  n  stderr                           else                             echo -e  ERROR MESSAGE  n  error message                       fi             fi     fi              PRINTING THE BACKTRACE                                                                                test -t 1  amp  amp  tput setf 7                                               white bold     echo -e   n  backtrace n               EXITING                                                                                test -t 1  amp  amp  tput setf 4                                               red bold     echo  Exiting        test -t 1  amp  amp  tput sgr0   Reset terminal      exit   error code    trap exit handler EXIT                                                          TRAP EXIT       trap exit ERR                                                                   TRAP ERR                                                                                      FUNCTION  BACKTRACE                                                                             function backtrace       local  start from  0      local params              if        params       gt    1             then              start from    1      fi      local i 0     local first false     while caller  i  gt   dev null     do         if test -n    start from    amp  amp       i    1    gt      start from                  then                 if test   first     false                     then                         echo  BACKTRACE IS                           first true                 fi                 caller  i         fi         let  i i 1      done    return 0     Example of usage  file content  trap-test sh     bin bash  source  lib trap sh   echo  doing something wrong now     echo   foo   exit 0    Running   bash trap-test sh   Output   doing something wrong now         EXIT HANDLER   FILE        trap-test sh LINE        6  ERROR CODE  1 ERROR MESSAGE  foo    unassigned variable  BACKTRACE IS  1 main trap-test sh  Exiting     As you can see from the screenshot below  the output is colored and the error message comes in the used language

User · Answer

This function has been serving me rather well recently   action            Test if the first parameter is non-zero       and return straight away if so     if test  1 -ne 0     then         return  1     fi        Discard the control parameter       and execute the rest     shift 1              local status           Test the exit status of the command run       and display an error message on failure     if test   status  -ne 0     then         echo Command          failed  gt  amp 2     fi      return   status      You call it by appending 0 or the last return value to the name of the command to run  so you can chain commands without having to check for error values   With this  this statement block   command1 param1 param2 param3    command2 param1 param2 param3    command3 param1 param2 param3    command4 param1 param2 param3    command5 param1 param2 param3    command6 param1 param2 param3      Becomes this   action 0 command1 param1 param2 param3    action    command2 param1 param2 param3    action    command3 param1 param2 param3    action    command4 param1 param2 param3    action    command5 param1 param2 param3    action    command6 param1 param2 param3      lt  lt  lt Error-handling code here gt  gt  gt    If any of the commands fail  the error code is simply passed to the end of the block   I find it useful when you don t want subsequent commands to execute if an earlier one failed  but you also don t want the script to exit straight away  for example  inside a loop

User · Answer

That s a fine solution  I just wanted to add  set -e   as a rudimentary error mechanism  It will immediately stop your script if a simple command fails  I think this should have been the default behavior  since such errors almost always signify something unexpected  it is not really  sane  to keep executing the following commands

User · Answer

Use a trap   tempfiles     cleanup       rm -f    tempfiles        trap cleanup 0  error       local parent lineno   1    local message   2    local code    3 -1     if    -n   message       then     echo  Error on or near line   parent lineno     message   exiting with status   code     else     echo  Error on or near line   parent lineno   exiting with status   code     fi   exit    code     trap  error   LINENO   ERR      then  whenever you create a temporary file   temp foo    mktemp -t foobar XXXXXX   tempfiles      temp foo      and  temp foo will be deleted on exit  and the current line number will be printed   set -e will likewise give you exit-on-error behavior  though it comes with serious caveats and weakens code s predictability and portability    You can either let the trap call error for you  in which case it uses the default exit code of 1 and no message  or call it yourself and provide explicit values  for instance   error   LINENO   the foobar failed  2   will exit with status 2  and give an explicit message

User · Answer

I use the following trap code  it also allows errors to be traced through pipes and  time  commands     bin bash set -o pipefail    trace ERR through pipes set -o errtrace    trace ERR through  time command  and other functions function error         JOB   0                 job name     LASTLINE   1            line of error occurrence     LASTERR   2             error code     echo  ERROR in   JOB    line   LASTLINE  with exit code   LASTERR       exit 1   trap  error   LINENO        ERR

User · Answer

Use a trap   tempfiles     cleanup       rm -f    tempfiles        trap cleanup 0  error       local parent lineno   1    local message   2    local code    3 -1     if    -n   message       then     echo  Error on or near line   parent lineno     message   exiting with status   code     else     echo  Error on or near line   parent lineno   exiting with status   code     fi   exit    code     trap  error   LINENO   ERR      then  whenever you create a temporary file   temp foo    mktemp -t foobar XXXXXX   tempfiles      temp foo      and  temp foo will be deleted on exit  and the current line number will be printed   set -e will likewise give you exit-on-error behavior  though it comes with serious caveats and weakens code s predictability and portability    You can either let the trap call error for you  in which case it uses the default exit code of 1 and no message  or call it yourself and provide explicit values  for instance   error   LINENO   the foobar failed  2   will exit with status 2  and give an explicit message

User · Answer

An equivalent alternative to  set -e  is  set -o errexit   It makes the meaning of the flag somewhat clearer than just  -e    Random addition  to temporarily disable the flag  and return to the default  of continuing execution regardless of exit codes   just use  set  e echo  commands run here returning non-zero exit codes will not cause the entire script to fail  echo  false returns 1 as an exit code  false set -e   This precludes proper error handling mentioned in other responses  but is quick  amp  effective  just like bash

User · Answer

Reading all the answers on this page inspired me a lot   So  here s my hint   file content  lib trap sh  lib name  trap  lib version 20121026  stderr log   dev shm stderr log       TO BE SOURCED ONLY ONCE                                                                              if test    g libs  lib name       then     return 0 else     if test    g libs        0  then         declare -A g libs     fi     g libs  lib name   lib version fi       MAIN CODE                                                                              set -o pipefail    trace ERR through pipes set -o errtrace    trace ERR through  time command  and other functions set -o nounset      set -u   exit the script if you try to use an uninitialised variable set -o errexit      set -e   exit the script if any statement returns a non-true return value  exec 2 gt   stderr log                                                                                 FUNCTION  EXIT HANDLER                                                                             function exit handler          local error code           test  error code    0  amp  amp  return               LOCAL VARIABLES        ------------------------------------------------------------------               local i 0     local regex        local mem         local error file        local error lineno        local error message  unknown       local lineno                  PRINT THE HEADER        ------------------------------------------------------------------             Color the output if it s an interactive terminal     test -t 1  amp  amp  tput bold  tput setf 4                                    red bold     echo -e   n    EXIT HANDLER  n                GETTING LAST ERROR OCCURRED                                                                                        Read last file from the error log       ------------------------------------------------------------------           if test -f   stderr log          then             stderr    tail -n 1   stderr log                rm   stderr log      fi              Managing the line to extract information        ------------------------------------------------------------------            if test -n   stderr          then                       Exploding stderr on               mem   IFS              local shrunk stderr    echo   stderr    sed  s        g                IFS                 local stderr parts    shrunk stderr               IFS   mem                 Storing information on the error             error file    stderr parts 0                error lineno    stderr parts 1                error message                 for    i   3  i  lt      stderr parts      i                      do                     error message   error message    stderr parts  i-1                   done                Removing last      colon character              error message    error message                     Trim             error message     echo   error message    sed -e  s     t        sed -e  s    t              fi              GETTING BACKTRACE                                                                                backtrace    backtrace 2                 MANAGING THE OUTPUT                                                                                local lineno        regex     a-z  1      0-9  1           if     error lineno     regex               The error line was found on the log            e g  type  ff  without quotes wherever            --------------------------------------------------------------         then             local row    BASH REMATCH 1                lineno    BASH REMATCH 2                 echo -e  FILE  t t  error file               echo -e    row     t t  lineno  n               echo -e  ERROR CODE  t  error code                            test -t 1  amp  amp  tput setf 6                                       white yellow             echo -e  ERROR MESSAGE  n error message            else             regex     error file       error file  s   s   error file  s   s   error file                 if       backtrace      regex                       The file was found on the log but not the error line                    could not reproduce this case so far                    ------------------------------------------------------                 then                     echo -e  FILE  t t error file                      echo -e  ROW  t tunknown n                       echo -e  ERROR CODE  t  error code                       test -t 1  amp  amp  tput setf 6                               white yellow                     echo -e  ERROR MESSAGE  n  stderr                      Neither the error line nor the error file was found on the log                    e g  type  cp ffd fdf  without quotes wherever                    ------------------------------------------------------                 else                                             The error file is the first on backtrace list                         Exploding backtrace on newlines                     mem  IFS                     IFS                                                                     Substring  I keep only the carriage return                        others needed only for tabbing purpose                      IFS   IFS 0 1                      local lines     backtrace                        IFS  mem                      error file                         if test -n    lines 1                            then                             array     lines 1                                  for    i 2  i lt    array      i                                      do                                     error file   error file   array  i                                done                                Trim                             error file     echo   error file    sed -e  s     t        sed -e  s    t                              fi                      echo -e  FILE  t t error file                      echo -e  ROW  t tunknown n                       echo -e  ERROR CODE  t  error code                       test -t 1  amp  amp  tput setf 6                               white yellow                     if test -n    stderr                           then                             echo -e  ERROR MESSAGE  n  stderr                           else                             echo -e  ERROR MESSAGE  n  error message                       fi             fi     fi              PRINTING THE BACKTRACE                                                                                test -t 1  amp  amp  tput setf 7                                               white bold     echo -e   n  backtrace n               EXITING                                                                                test -t 1  amp  amp  tput setf 4                                               red bold     echo  Exiting        test -t 1  amp  amp  tput sgr0   Reset terminal      exit   error code    trap exit handler EXIT                                                          TRAP EXIT       trap exit ERR                                                                   TRAP ERR                                                                                      FUNCTION  BACKTRACE                                                                             function backtrace       local  start from  0      local params              if        params       gt    1             then              start from    1      fi      local i 0     local first false     while caller  i  gt   dev null     do         if test -n    start from    amp  amp       i    1    gt      start from                  then                 if test   first     false                     then                         echo  BACKTRACE IS                           first true                 fi                 caller  i         fi         let  i i 1      done    return 0     Example of usage  file content  trap-test sh     bin bash  source  lib trap sh   echo  doing something wrong now     echo   foo   exit 0    Running   bash trap-test sh   Output   doing something wrong now         EXIT HANDLER   FILE        trap-test sh LINE        6  ERROR CODE  1 ERROR MESSAGE  foo    unassigned variable  BACKTRACE IS  1 main trap-test sh  Exiting     As you can see from the screenshot below  the output is colored and the error message comes in the used language

User · Answer

Using trap is not always an option  For example  if you re writing some kind of re-usable function that needs error handling and that can be called from any script  after sourcing the file with helper functions   that function cannot assume anything about exit time of the outer script  which makes using traps very difficult  Another disadvantage of using traps is bad composability  as you risk overwriting previous trap that might be set earlier up in the caller chain   There is a little trick that can be used to do proper error handling without traps  As you may already know from other answers  set -e doesn t work inside commands if you use    operator after them  even if you run them in a subshell  e g   this wouldn t work      bin sh    prints      -- gt  outer   -- gt  inner     so 1 sh  line 16  some failed command  command not found    lt -- inner    lt -- outer  set -e  outer       echo  -- gt  outer     inner           exit code        echo  -- gt  cleanup      return  exit code       echo   lt -- outer     inner       set -e   echo  -- gt  inner    some failed command   echo   lt -- inner     outer   But    operator is needed to prevent returning from the outer function before cleanup  The trick is to run the inner command in background  and then immediately wait for it  The wait builtin will return the exit code of the inner command  and now you re using    after wait  not the inner function  so set -e works properly inside the latter      bin sh    prints      -- gt  outer   -- gt  inner     so 2 sh  line 27  some failed command  command not found   -- gt  cleanup  set -e  outer       echo  -- gt  outer    inner  amp    wait             exit code        echo  -- gt  cleanup      return  exit code       echo   lt -- outer     inner       set -e   echo  -- gt  inner    some failed command   echo   lt -- inner     outer   Here is the generic function that builds upon this idea  It should work in all POSIX-compatible shells if you remove local keywords  i e  replace all local x y with just x y      CLEANUP cleanup cmd  run cmd  args          cmd  and  args     A command to run and its arguments       cleanup cmd  A command that is called after cmd has exited    and gets passed the same arguments as cmd  Additionally  the   following environment variables are available to that command      -  RUN CMD  contains the  cmd  that was passed to  run     -  RUN EXIT CODE  contains the exit code of the command      If  cleanup cmd  is set   run  will return the exit code of that   command  Otherwise  it will return the exit code of  cmd     run       local cmd   1   shift   local exit code 0    local e was set 1  if   is shell attribute set e  then     set -e     e was set 0   fi      cmd        amp     wait             exit code           if     e was set    0    amp  amp  is shell attribute set e  then     set  e   fi    if   -n   CLEANUP     then     RUN CMD   cmd  RUN EXIT CODE   exit code    CLEANUP           return      fi    return  exit code     is shell attribute set       attribute  like  x    case   -  in        1    return 0              return 1      esac     Example of usage      bin sh set -e    Source the file with the definition of  run   previous code snippet     Alternatively  you may paste that code directly here and comment the next line      utils sh   main       echo  -- gt  main        CLEANUP cleanup run inner        echo   lt -- main      inner       echo  -- gt  inner        sleep 0 5  if     1     fail     then     oh my god look at this   fi   echo   lt -- inner      cleanup       echo  -- gt  cleanup        echo      RUN CMD     RUN CMD     echo      RUN EXIT CODE    RUN EXIT CODE    sleep 0 3   echo   lt -- cleanup    return  RUN EXIT CODE    main        Running the example       so 3 fail  echo  exit code       -- gt  main  fail -- gt  inner  fail   so 3  line 15  oh my god look at this  command not found -- gt  cleanup  fail     RUN CMD    inner      RUN EXIT CODE   127  lt -- cleanup exit code  127      so 3 pass  echo  exit code       -- gt  main  pass -- gt  inner  pass  lt -- inner -- gt  cleanup  pass     RUN CMD    inner      RUN EXIT CODE   0  lt -- cleanup  lt -- main exit code  0   The only thing that you need to be aware of when using this method is that all modifications of Shell variables done from the command you pass to run will not propagate to the calling function  because the command runs in a subshell

User · Answer

This trick is useful for missing commands or functions   The name of the missing function  or executable  will be passed in      function handle error       status        last call  1        127 is  command not found         status    127     amp  amp  return      echo  you tried to call  last call      return      Trap errors  trap  handle error       ERR

User · Answer

Another consideration is the exit code to return. Just "1" is pretty standard, although there are a handful of reserved exit codes that bash itself uses, and that same page argues that user-defined codes should be in the range 64-113 to conform to C/C++ standards.

You might also consider the bit vector approach that mount uses for its exit codes:

 0  success
 1  incorrect invocation or permissions
 2  system error (out of memory, cannot fork, no more loop devices)
 4  internal mount bug or missing nfs support in mount
 8  user interrupt
16  problems writing or locking /etc/mtab
32  mount failure
64  some mount succeeded

OR-ing the codes together allows your script to signal multiple simultaneous errors.

User · Answer

This has served me well for a while now  It prints error or warning messages in red  one line per parameter  and allows an optional exit code     Custom errors EX UNKNOWN 1  warning           Output warning messages       Color the output red if it s an interactive terminal        param  1     Messages      test -t 1  amp  amp  tput setf 4      printf   s n        gt  amp 2      test -t 1  amp  amp  tput sgr0   Reset terminal     true    error           Output error messages with optional exit code        param  1     Messages        param  N  Exit code  optional       messages                 If the last parameter is a number  it s not part of the messages     last parameter    messages     -1       if      last parameter       0-9           then         exit code  last parameter         unset messages       messages     - 1        fi      warning    messages           exit   exit code - EX UNKNOWN

User · Answer

Inspired by the ideas presented here  I have developed a readable and convenient way to handle errors in bash scripts in my bash boilerplate project    By simply sourcing the library  you get the following out of the box  i e   it will halt execution on any error  as if using set -e thanks to a trap on ERR and some bash-fu      There are some extra features that help handle errors  such as try and catch  or the throw keyword  that allows you to break execution at a point to see the backtrace  Plus  if the terminal supports it  it spits out powerline emojis  colors parts of the output for great readability  and underlines the method that caused the exception in the context of the line of code   The downside is - it s not portable - the code works in bash  probably    4 only  but I d imagine it could be ported with some effort to bash 3    The code is separated into multiple files for better handling  but I was inspired by the backtrace idea from the answer above by Luca Borrione    To read more or take a look at the source  see GitHub   https   github com niieani bash-oo-framework error-handling-with-exceptions-and-throw

User · Answer

Inspired by the ideas presented here  I have developed a readable and convenient way to handle errors in bash scripts in my bash boilerplate project    By simply sourcing the library  you get the following out of the box  i e   it will halt execution on any error  as if using set -e thanks to a trap on ERR and some bash-fu      There are some extra features that help handle errors  such as try and catch  or the throw keyword  that allows you to break execution at a point to see the backtrace  Plus  if the terminal supports it  it spits out powerline emojis  colors parts of the output for great readability  and underlines the method that caused the exception in the context of the line of code   The downside is - it s not portable - the code works in bash  probably    4 only  but I d imagine it could be ported with some effort to bash 3    The code is separated into multiple files for better handling  but I was inspired by the backtrace idea from the answer above by Luca Borrione    To read more or take a look at the source  see GitHub   https   github com niieani bash-oo-framework error-handling-with-exceptions-and-throw

[bash] Error handling in Bash

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