Bash script error unary operator expected

Question

In my script I am trying to error check if the first and only argument is equal to -v but it is an optional argument  I use an if statement but I keep getting the unary operator expected error    this is the code   if    1    -v    then    echo  usage   0  -v      exit fi   Edit   I should be more specific   This part of the script above is checking an optional argument and then after  if the argument is not entered  it should run the rest of the program       bin bash  if        -gt  1     then    echo  usage   0  -v      exit fi  if     1     -v    then    echo  usage   0  -v      exit fi  if     1    -v    then    echo   ps -ef   grep -v        else    echo   ps -ef   grep        grep root   fi

User · Answer

Quotes   if     1     -v    then   Otherwise  when  1 is completely empty  your test becomes        -v     instead of          -v        and    is not a unary operator  that is  one capable of taking only a single argument

User · Answer

Or for what seems like rampant overkill  but is actually simplistic     Pretty much covers all of your cases  and no empty string or unary concerns   In the case the first arg is  -v   then do your conditional ps -ef  else in all other cases throw the usage      bin sh case  1 in    -v   if     1    -v    then          echo   ps -ef   grep -v                else          echo   ps -ef   grep        grep root           fi           echo  usage   0  -v           exit 1    It is good practice to throw a code  hence allowing    check esac   If one cares not where the  -v  arg is  then simply drop the case inside a loop  The would allow walking all the args and finding  -v  anywhere  provided it exists   This means command line argument order is not important  Be forewarned  as presented  the variable arg match is set  thus it is merely a flag   It allows for multiple occurrences of the  -v  arg  One could ignore all other occurrences of  -v  easy enough       bin sh  usage         echo  usage   0  -v     exit 1     unset arg match  for arg in     do   case  arg in      -v   if     arg    -v    then            echo   ps -ef   grep -v                  else            echo   ps -ef   grep        grep root             fi           arg match 1     this is set  but could increment                 esac done  if      arg match    then   usage fi   But  allow multiple occurrences of an argument is convenient to use in situations such as      adduser -u sam -s -f -u bob -trace -verbose   We care not about the order of the arguments  and even allow multiple -u arguments  Yes  it is a simple matter to also allow     adduser -u sam -s -f -u bob -trace -verbose

[bash] Bash script error [: !=: unary operator expected

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