/bin/sh: Odd string comparison error 'unexpected operator' [duplicate]

问题

Found this error to be quite weird because previously my script was working and but after I moved it from the server I was working on to my local machine, it stopped working and just gave me an 'unexpected operator' error.

# Else if the script is being run in the arrayscripts directory, add /output/ ...
elif [ $basePath == "arrayscripts" ];
then
        echo "$dscr has started to run."
        cpuPath="`pwd`/output/cpu.binary"
        txtPath="`pwd`/output/cpu.txt"
        csvPath="`pwd`/output/cpu.csv"

回答1:

If your actual shell is /bin/sh [contrary to the initial question, but as discussion commentary has made clear], use = rather than == in your test expression:

elif [ "$basePath" = arrayscripts ]

Note that the right-hand side doesn't need to be quoted in this case, since it contains no expansions and no syntactically-sensitive characters.

Alternately, if this issue is reproducible when using bash, the obvious problem is missing quotes.

Use either

[ "$basePath" = arrayscripts ] # this is POSIX compatible

[[ $basePath = arrayscripts ]] # this works only with bash

Otherwise, the number of arguments $basePath expands into is undefined -- it may expand into zero arguments, making the statement

[ = arrayscripts ]

...which would try to use = as a unary operator, which it isn't...

or if $basePath contained, say, "true -o bar =", it could expand into something like

[ true -o bar = arrayscripts ]

...resulting in program behavior very different from what you actually want.

Bottom line: When writing for shells which follow POSIX rules (basically, anything but zsh or fish), quote your expansions unless you have a specific and compelling reason to do otherwise. (Use of the bash/ksh extension [[ ]] provides such a reason, by introducing a context in which string-splitting of expansion results and glob expansion don't take place).

回答2:

This is an error you'd get if you were executing the script with a POSIX shell like dash. dash is the default /bin/sh on some platforms such as Ubuntu and Debian.

== is specific to bash ( Bashism ) and is not compatible with POSIX shells like dash, which uses only = to test string equality.

In the context of single brackets, == and = are treated as the same operator in bash, so either can be used.

回答3:

I managed to get my script working by changing the comparison function from '==' to '=' as suggested by 'alister' in the unix and linux forums ( http://www.unix.com/shell-programming-and-scripting/141856-how-avoid-unexpected-operator-error-when-comparing-2-strings.html ) and so my script looked like this

# Else if the script is being run in the arrayscripts directory, add /output/ ...
    elif [ "$basePath" = "arrayscripts" ];
    then
            echo "$dscr has started to run."
            cpuPath="`pwd`/output/cpu.binary"
            txtPath="`pwd`/output/cpu.txt"
            csvPath="`pwd`/output/cpu.csv"

Hope that if anyone gets this same error as I did, that this answer will help them. .

来源：https://stackoverflow.com/questions/25846454/bin-sh-odd-string-comparison-error-unexpected-operator

标签

shell