CODEWITHSUNDEEP
ksh
spaceworld
spaceworld

Reputation: 13

Why IFS impact subshell variable?

This KSH code working fine on AIX and RH with the standard IFS (default)

[ "$(uname)" = "AIX" ] && ECHO="echo" || ECHO="echo -e"
echo "AA BB CC DD" | while read a b c d; do
[ "`$ECHO $a | cut -c1-2`" = "AA" ] && echo $b
done

If i set a different IFS like a ; for example

[ "$(uname)" = "AIX" ] && ECHO="echo" || ECHO="echo -e"
IFS=";"
echo "AA;BB;CC;DD" | while read a b c d; do
[ "`$ECHO $a | cut -c1-2`" = "AA" ] && echo $b
done

I get an error like only on RH not Aix

+ echo 'AA;BB;CC;DD'
+ read a b c d
+ cut -c1-2
+ 'echo -e' AA
-ksh: line 3: echo -e: not found
+ [ '' '=' AA ]
+ read a b c d
+ echo .....
+ cut -d. -f1

Someone can explain me why this is happening and how we can solved it without a eval ? Thanks for your time :-)

Upvotes: 0

Views: 198

Answers (1)

glenn jackman
glenn jackman

Reputation: 246877

You have ECHO="echo -e", then you set IFS=";", so when you expand $ECHO unquoted (where globbing and word splitting will take effect), you get echo -e as a single word (because you are word splitting using semicolon not whitespace), and of course there's no such command.

You'll want to refer to I'm trying to put a command in a variable, but the complex cases always fail. The answer is to use an array:

[ "$(uname)" = "AIX" ] && ECHO=(echo) || ECHO=(echo -e)

And then, use it like 

"${ECHO[@]}" "$a" | cut -c1-2

You'll also need to use quotes more. Refer to Security implications of forgetting to quote a variable in bash/POSIX shells

(todo: discuss not using "echo -e"...)

Upvotes: 2

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