Unexpected operator in shell programming

Question

My code          bin sh      filename choose sh     read choose         choose      y  -o   choose      Y     amp  amp  echo  Yes   amp  amp  exit 0         choose      n  -o   choose      N     amp  amp  echo  No    amp  amp  exit 0     echo  Wrong Input   amp  amp  exit 0   But when I execute       sh   choose sh   terminal prompt me that        4  n   Unexpected operator       5  n   Unexpected operator   Is there any mistake in my bash script  Thanks

User · Answer

In fact the     square opening bracket is just an internal shell alias for the test command   So you can say   test -f   bin bash   amp  amp  echo  This system has a bash shell    or    -f   bin bash     amp  amp  echo  This system has a bash shell        they are equivalent in either sh or bash   Note the requirement to have a closing     bracket on the     command but other than that     is the same as  test     man test  is a good thing to read

User · Answer

POSIX sh doesn t understand    for string equality  as that is a bash-ism  Use   instead   The other people saying that brackets aren t supported by sh are wrong  btw

User · Answer

Do not use any reserved keyword as the start of any variable name  eg HOSTNAME will fail as HOST  TYPE NAME  are reserved

User · Answer

you can use case esac instead of if else  case   choose  in    yY   echo  Yes   amp  amp  exit      nN   echo  No   amp  amp  exit         echo  wrong input   amp  amp  exit   esac

User · Answer

There is no mistake in your bash script  But you are executing it with sh which has a less extensive syntax     So  run bash   choose sh instead

User · Answer

you have to use bash instead or rewrite your script using standard sh   sh -c  test   choose     y  -o   choose     Y

User · Answer

To execute it with Bash  use    bin bash and chmod it to be executable  then use    choose sh

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