How to debug a bash script

Question

Is there any way to debug a bash script  E g something that prints a sort of execution log like  calling line 1    calling line 2  etc

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I built a Bash debugger  Just give it a try  I hope it will help  https   sourceforge net projects bashdebugingbash

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Install VSCode  then add bash debug extension and you are ready to debug in visual mode  see Here in action

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Use eclipse with the plugins shelled  amp  basheclipse   https   sourceforge net projects shelled  source directory https   sourceforge net projects basheclipse  source directory  For shelled  Download the zip and import it into eclipse via help -  install new software   local archive For basheclipse  Copy the jars into dropins directory of eclipse  Follow the steps provides https   sourceforge net projects basheclipse files  source navbar    I wrote a tutorial with many screenshots at http   dietrichschroff blogspot de 2017 07 bash-enabling-eclipse-for-bash html

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I found shellcheck utility and may be some folks find it interesting https   github com koalaman shellcheck  A little example     cat test sh  ARRAY   hello there  world   for x in  ARRAY  do   echo  x done    shellcheck test sh   In test sh line 3  for x in  ARRAY  do           -- SC2128  Expanding an array without an index only gives the first element    fix the bug  first try       cat test sh        ARRAY   hello there  world   for x in   ARRAY      do   echo  x done    shellcheck test sh  In test sh line 3  for x in   ARRAY      do           -- SC2068  Double quote array expansions  otherwise they re like    and break on spaces    Let s try again       cat test sh  ARRAY   hello there  world   for x in    ARRAY       do   echo  x done    shellcheck test sh   find now   It s just a small example

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There s good amount of detail on logging for shell scripts via global varaibles of shell  We can emulate the similar kind of logging in shell script  http   www cubicrace com 2016 03 log-tracing-mechnism-for-shell-scripts html   The post has details on introdducing log levels like INFO   DEBUG  ERROR  Tracing details like script entry  script exit  function entry  function exit   Sample log

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Some trick to debug bash scripts   Using set - nvx   In addition to   set -x   and  set  x   for stopping dump   I would like to speak about set -v wich dump as smaller as less developped output   bash  lt  lt  lt   set -x nfor i in  0  9  do n techo  i n tdone nset  x  2 gt  amp 1  gt  dev null wc -l 21  for arg in x v n nx nv nvx do echo  - opts   arg      bash 2 gt   gt  wc -l sed s   stderr     gt   gt  wc -l sed s   stdout     lt  lt eof         set - arg         for i in  0  9  do             echo  i           done         set   arg         echo Done  eof     sleep  02   done - opts  x stdout 11 stderr 21 - opts  v stdout 11 stderr 4 - opts  n stdout 0 stderr 0 - opts  nx stdout 0 stderr 0 - opts  nv stdout 0 stderr 5 - opts  nvx stdout 0 stderr 5   Dump variables or tracing on the fly  For testing some variables  I use sometime this   bash  lt  sed  18ideclare  gt  amp 2 -p var1 var2  myscript sh  args   for adding   declare  gt  amp 2 -p var1 var2   at line 18 and running resulting script  with args   without having to edit them   of course  this could be used for adding set   -  nvx    bash  lt  sed  18s    ndeclare -p v1 v2  gt   amp 2  22s   set -x n  26s   set  x n   myscript  args   will add declare -p v1 v2  gt  amp 2 after line 18  set -x before line 22 and set  x before line 26   little sample   bash  lt  sed  2 3s    ndeclare -p LINENO i v2  gt   amp 2  5s   set -x n  7s   set  x n    lt           seq -f  echo        i  g    1 8   arg1 arg2 arg1 arg2  1 arg1 arg2  2 declare -i LINENO  3  declare -- i  2   dev fd 63  line 3  declare  v2  not found arg1 arg2  3 declare -i LINENO  5  declare -- i  3   dev fd 63  line 5  declare  v2  not found arg1 arg2  4   echo arg1 arg2  5 arg1 arg2  5   echo arg1 arg2  6 arg1 arg2  6   set  x arg1 arg2  7 arg1 arg2  8   Note  Care about  LINENO will be affected by on-the-fly modifications     To see resulting script whithout executing  simply drop bash  lt   and   arg1 arg2    Step by step  execution time  Have a look at my answer about how to profile bash scripts

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set  x    ECHO OFF  set -x    ECHO ON      You can add -xv option to the standard Shebang as follows        bin bash -xv     -x   Display commands and their arguments as they are executed  -v   Display shell input lines as they are read       ltrace is another Linux Utility similar to strace  However  ltrace lists all the library calls being called in an executable or a running process  Its name itself comes from library-call tracing  For example      ltrace   executable  lt parameters gt    ltrace -p  lt PID gt      Source

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sh -x script  arg1      bash -x script  arg1        These give you a trace of what is being executed    See also  Clarification  near the bottom of the answer    Sometimes  you need to control the debugging within the script   In that case  as Cheeto reminded me  you can use   set -x   This turns debugging on   You can then turn it off again with   set  x    You can find out the current tracing state by analyzing  -  the current flags  for x    Also  shells generally provide options  -n  for  no execution  and  -v  for  verbose  mode  you can use these in combination to see whether the shell thinks it could execute your script     occasionally useful if you have an unbalanced quote somewhere     There is contention that the  -x  option in Bash is different from other shells  see the comments    The Bash Manual says    -x  Print a trace of simple commands  for commands  case commands  select commands  and arithmetic for commands and their arguments or associated word lists after they are expanded and before they are executed  The value of the PS4 variable is expanded and the resultant value is printed before the command and its expanded arguments     That much does not seem to indicate different behaviour at all   I don t see any other relevant references to  -x  in the manual   It does not describe differences in the startup sequence   Clarification  On systems such as a typical Linux box  where   bin sh  is a symlink to   bin bash   or wherever the Bash executable is found   the two command lines achieve the equivalent effect of running the script with execution trace on   On other systems  for example  Solaris  and some more modern variants of Linux    bin sh is not Bash  and the two command lines would give  slightly  different results   Most notably    bin sh  would be confused by constructs in Bash that it does not recognize at all    On Solaris   bin sh is a Bourne shell  on modern Linux  it is sometimes Dash     a smaller  more strictly POSIX-only shell    When invoked by name like this  the  shebang  line      bin bash  vs     bin sh   at the start of the file has no effect on how the contents are interpreted   The Bash manual has a section on Bash POSIX mode which  contrary to a long-standing but erroneous version of this answer  see also the comments below   does describe in extensive detail the difference between  Bash invoked as sh  and  Bash invoked as bash    When debugging a  Bash  shell script  it will be sensible and sane     necessary even     to use the shell named in the shebang line with the -x option   Otherwise  you may  will   get different behaviour when debugging from when running the script

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I think you can try this Bash debugger  http   bashdb sourceforge net

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This answer is valid and useful  https   stackoverflow com a 951352  But  I find that the  standard  script debugging methods are inefficient  unintuitive  and hard to use   For those used to sophisticated GUI debuggers that put everything at your fingertips and make the job a breeze for easy problems  and possible for hard problems   these solutions aren t very satisfactory   What I do is use a combination of DDD and bashdb    The former executes the latter  and the latter executes your script   This provides a multi-window UI with the ability to step through code in context and view variables  stack  etc   without the constant mental effort to maintain context in your head or keep re-listing the source   There is guidance on setting that up here  http   ubuntuforums org showthread php t 660223

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You can also write  set -x  within the script

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I ve used the following methods to debug my script   set -e makes the script stop immediately if any external program returns a non-zero exit status   This is useful if your script attempts to handle all error cases and where a failure to do so should be trapped   set -x was mentioned above and is certainly the most useful of all the debugging methods   set -n might also be useful if you want to check your script for syntax errors   strace is also useful to see what s going on   Especially useful if you haven t written the script yourself

[bash] How to debug a bash script?

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