How to exit if a command failed

Question

I am a noob in shell-scripting  I want to print a message and exit my script if a command fails  I ve tried   my command  amp  amp   echo  my command failed  exit    but it does not work  It keeps executing the instructions following this line in the script  I m using Ubuntu and bash

User · Answer

You can also use  if you want to preserve exit error status  and have a readable file with one command per line   my command1    exit    my command2    exit      This  however will not print any additional error message  But in some cases  the error will be printed by the failed command anyway

User · Answer

Using exit directly may be tricky as the script may be sourced from other places  e g  from terminal   I prefer instead using subshell with set -e  plus errors should go into cerr  not cout    set -e ERRCODE 0 my command    ERRCODE    test  ERRCODE    0          gt  amp 2 echo  quot My command failed   ERRCODE  quot   exit  ERRCODE

User · Answer

The other answers have covered the direct question well  but you may also be interested in using set -e  With that  any command that fails  outside of specific contexts like if tests  will cause the script to abort  For certain scripts  it s very useful

User · Answer

I ve hacked up the following idiom   echo  Generating from IDL     idlj -fclient -td java src echo idl if      -ne 0    then   echo  Failed  aborting     exit 1    fi  echo  Compiling classes     javac  java if      -ne 0    then   echo  Failed  aborting     exit 1    fi  echo  Done     Precede each command with an informative echo  and follow each command with that same  if      -ne 0       line    Of course  you can edit that error message if you want to

User · Answer

If you want that behavior for all commands in your script  just add     set -e    set -o pipefail   at the beginning of the script  This pair of options tell the bash interpreter to exit whenever a command returns with a non-zero exit code   This does not allow you to print an exit message  though

User · Answer

Try   my command      echo  my command failed    exit 1      Four changes    Change  amp  amp  to    Use     in place of     Introduce   after exit and spaces after   and before     Since you want to print the message and exit only when the command fails   exits with non-zero value  you need a    not an  amp  amp    cmd1  amp  amp  cmd2   will run cmd2 when cmd1 succeeds exit value 0   Where as  cmd1    cmd2   will run cmd2 when cmd1 fails exit value non-zero    Using     makes the command inside them run in a sub-shell and calling a exit from there causes you to exit the sub-shell and not your original shell  hence execution continues in your original shell   To overcome this use      The last two changes are required by bash

User · Answer

The trap shell builtin allows catching signals  and other useful conditions  including failed command execution  i e   a non-zero return status   So if you don t want to explicitly test return status of every single command you can say trap  your shell code  ERR and the shell code will be executed any time a command returns a non-zero status  For example   trap  echo script failed  exit 1  ERR   Note that as with other cases of catching failed commands  pipelines need special treatment  the above won t catch false   true

User · Answer

Note also  each command s exit status is stored in the shell variable     which you can check immediately after running the command  A non-zero status indicates failure   my command if      -eq 0   then     echo  it worked  else     echo  it failed  fi

User · Answer

Provided my command is canonically designed  ie returns 0 when succeeds  then  amp  amp  is exactly the opposite of what you want  You want      Also note that   does not seem right to me in bash  but I cannot try from where I am  Tell me   my command          echo  my command failed        exit 1

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