Properly splitting a string in UNIX shell

Question

I need to be able to split a string so that each string are passed as variable in my shell.

I tried something like this:

$ cat test.sh
#!/bin/sh

COMPOPT="CC=clang CXX=clang++"
$COMPOPT cmake ../gdcm

I also tried a bash specific solution, but with no luck so far:

$ cat test.sh
#!/bin/bash -x

COMPOPT="CC=clang CXX=clang++"
ARRAY=($COMPOPT)
"${ARRAY[0]}" "${ARRAY[1]}" cmake ../gdcm

I always get the non-informative error message:

./test.sh: 5: ./t.sh: CC=clang: not found

Of course if I try directly from the running shell this works:

$ CC=clang CXX=clang++ cmake ../gdcm

chepner · Accepted Answer · 2014-02-11 17:44:27Z

2

Another eval-free solution is to use the env program:

env "${ARRAY[@]}" cmake ../gdm

which provides a level of indirection to the usual FOO=BAR command syntax.

answered Feb 11, 2014 at 17:44

chepner

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Comments

devnull · Accepted Answer · 2014-02-11 17:15:32Z

1

When you say:

$COMPOPT cmake ../gdcm

the shell would attempt to execute the value of the variable as a command.

The evil eval is rather handy in such cases. Say:

eval $COMPOPT cmake ../gdcm

answered Feb 11, 2014 at 17:15

devnull

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Comments

anubhava · Accepted Answer · 2014-02-11 17:27:38Z

1

Though devnull's answer works but uses eval and that has known pitfalls.

Here is a way it can be done without invoking eval:

#!/bin/sh

COMPOPT="CC=clang CXX=clang++"
sh -c "$COMPOPT cmake ../gdcm"

i.e. pass the whole command line to sh (or bash).

answered Feb 11, 2014 at 17:27

anubhava

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2 Comments

user49586 Over a year ago

How is that safer than using eval? If $COMPOPT is set to rm -rf /; , it will still get executed, no?

anubhava Over a year ago

No I never claimed on safety, writing shell script has its own risk if one is not careful.

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