How to check if is not equal to zero in unix shell scripting

Question

I have a script which uses test command to check if     return code of last executed command  is not equal to zero  The code is as follows  -     is the exit status of the last command executed   if  test    -ne 0  then   statements   fi   However this way of validation does not work for strings as get syntax error   Please suggest a suitable alternative to this

User · Answer

This is a solution that came up with for a similar issue  exit status      if        0   then     true else     false fi     usage   do-command exit status  amp  amp  echo  worked     echo  didnt work

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if    var1     var2    then  echo   var1  else  echo   var2  fi

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I don t know how you got a string in    but you can do   if     x        x0      then    echo good fi

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Put it in a variable first and then try to test it  as shown below  ret    if    ret -ne 0    then         echo  In If  else         echo  In Else  fi   This should help     Edit  If the above is not working as expected then  there is a possibility that you are not using     at right place  It must be the very next line after the command of which you need to catch the return status  Even if there is any other single command in between the target and you catching it s return status  you ll be retrieving the returns status of this intermediate command and not the one you are expecting

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put set -o pipefail at start of any script  to return any failure  incase you do  and the test fails but the tee doesnt  By default    just takes the last commands success  in this case the  tee  command  test   tee  tmp dump      -ne 0    amp  amp  echo  failed

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Try this after execution of your script   if      -ne 0    then   statements   fi

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lt run your last command on this line gt  a      if     a  -ne 0    then echo  do something   fi   use whatever command you want to use instead of the echo  do something  command

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You don t need to test if    is not 0  The shell provides  amp  amp  and    so you can easily branch based on implicit result of that test  some command  amp  amp          executes this block of code        if some command would result in      -eq 0              executes this block of code        if some command would result in      -ne 0    You can remove either branch  depending on what you want  So if you just want to test for failure  i e     -ne 0   some command returning nonzero            executes this block of code when         -ne 0       and nothing if the command succeeds      -eq 0    However  the code you provided in the question works  as is  I m confused that you got syntax errors  amp  concluded that    was a string  It s most likely that the errant code causing the syntax error was not provided with the question  This is especially evident because you claim that no one else s solutions work either  When this happens  you have to re-evaluate your assumptions  NB  The code above may give confusing results if the code inside the braces returns an error  In that case simply use the if command instead  like this  if some command  then       executes this block of code        if some command would result in      -eq 0 else       executes this block of code        if some command would result in      -ne 0 fi

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function assert exit code       rc     if     rc    0     then echo   1  1 gt  amp 2  fi          execute sh  assert exit code  execute sh has failed

User · Answer

I put together some code that may help to see how return value vs returned strings works  There may be a better way  but this is what I found through testing     bin sh     ro    pass      echo passed   return 0      no errors   fail      echo failed   return 1      has an error   t      echo true  has error   f      echo false  no error    dv   printf  quot  60s quot    dv   dv    -   echo return code good for one use  not available for echo echo  dv pass      -gt 0    amp  amp  t    f echo  quot function pass         quot    return value is gone  echo fail      -gt 0    amp  amp  t    f echo  quot function fail         quot    return value is gone  echo  echo save return code to var k for continued usage echo  dv pass k       k -gt 0    amp  amp  t    f echo  quot function pass    k  k quot  echo fail k       k -gt 0    amp  amp  t    f echo  quot function fail    k  k quot  echo    direct evaluation of the return value   note that       and        executes in a subshell   with return value to calling shell           is for math string evaluation  echo direct evaluations of the return value  echo    by if  pass  and if  fail   echo  dv if  pass   then   echo pass has no errors else   echo pass has errors fi if  fail   then   echo fail has no errors else   echo fail has errors fi    this code results in error because of returned string  stdout    but comment out the echo statements in pass fail functions and this code succeeds echo echo    by if   pass  and if   fail    this succeeds if no echo to stdout from function  echo  dv if   pass   then   echo pass has no errors else   echo pass has errors fi if   fail   then   echo fail has no errors else   echo fail has errors fi  echo echo    by if   pass   and if   fail     this always fails  echo  dv if   pass    then   echo pass has no errors else   echo pass has errors fi if   fail    then   echo fail has no errors else   echo fail has errors fi  echo  s   pass  r    echo pass   quot s   s     r   r quot  s   fail  r    echo fail   quot s   s     r   r quot

[shell] How to check if $? is not equal to zero in unix shell scripting?

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