My code:
#!/bin/sh
#filename:choose.sh
read choose
[ "$choose" == "y" -o "$choose" == "Y" ] && echo "Yes" && exit 0
[ "$choose" == "n" -o "$choose" == "N" ] && echo "No" && exit 0
echo "Wrong Input" && 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!
There is no mistake in your bash script. But you are executing it with sh which has a less extensive syntax
So, you'll need run bash ./choose.sh instead, or convert the script to use POSIX compliant sh commands only, such as = between strings instead of ==.
bash syntax is a superset of sh syntax - the /bin/sh executable on your system may provide only standard sh functionality, in which []-style tests are not included.
#!/bin/bash and making the file executable, and just running ./choose.sh.
sh supports [. == works in Bash built-ins [[, test and [ while a single = is required by POSIX version of [ and test. (Bash manual says the same, BTW.) Requiring Bash because of this is needless harm to portability. Command name is [ or test, ] is just non-necessary, unused last parameter. Many shells implement these as built-ins, as Wikipedia says.
[ command correctly. It is in syntax of the [ command parameters, which is not sh’s business. Second, Bash is overkill for such a job, especially when a much simpler solution exists. This is not really wrong as it solves the problem too, but I think it is generally bad advice. This leads beginners to false conclusion that Bash solves their problems. It has many unportable extensions over POSIX-required features. I believe we should lead beginners to writing portable programs.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.
To execute it with Bash, use #!/bin/bash and chmod it to be executable, then use
./choose.sh
you can use case/esac instead of if/else
case "$choose" in
[yY]) echo "Yes" && exit;;
[nN]) echo "No" && exit;;
* ) echo "wrong input" && exit;;
esac
you have to use bash instead or rewrite your script using standard sh
sh -c 'test "$choose" = "y" -o "$choose" = "Y"'
In fact the "[" square opening bracket is just an internal shell alias for the test command.
So you can say:
test -f "/bin/bash" && echo "This system has a bash shell"
or
[ -f "/bin/bash" ] && echo "This system has a bash shell"
... they are equivalent in either sh or bash. Note the requirement to have a closing "]" bracket on the "[" command but other than that "[" is the same as "test". "man test" is a good thing to read.
Do not use any reserved keyword as the start of any variable name: eg HOSTNAME will fail as HOST {TYPE|NAME} are reserved
shtobash. Some distributions don't offer a trueshanymore. Although some will argue (and I tend to agree) that if you're writing a script to be portable, write it inshinstead ofbash.source foobar.shnot./foobar.sh${choose}BLAHapproach -- it's much better to just quote, with"$choose"; constant prefixes/suffixes haven't been needed since the 1970s (as long as features marked obsolescent in the current POSIXteststandard, like-aor-o, are avoided).