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Meaning of WINPORT=22${WINPORT:+:}${WINPORT:-}

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# 1  
Old 10-09-2013
Meaning of WINPORT=22${WINPORT:+:}${WINPORT:-}
Hi all,

O/S: Sun Solaris SPARC 64 bits

Could anyone please explain what does the below mean after WINPORT=22 in the below line?

Code:
WINPORT=22${WINPORT:+:}${WINPORT:-}

${WINPORT:+:}${WINPORT:-} ???

On doing echo $WINPORT, I get the port value as:

22

Thanks,
a1_win
# 2  
Old 10-09-2013
Set WINPORT to 22 followed by... if WINPORT was already set, substitute all of it for a colon (${WINPORT:+:}) followed by the original value of WINPORT (${WINPORT:-} - not sure what purpose the :- serves here).

From man bash:
Code:
       ${parameter:+word}
              Use  Alternate Value.  If parameter is null or unset, nothing is substituted, otherwise the expansion of
              word is substituted.

This User Gave Thanks to Scott For This Post:
rbatte1
# 3  
Old 10-09-2013
Hi Scott,

Tried the below and verified

Code:
echo $WINPORT
22

echo ${WINPORT:+:}
:

echo ${WINPORT:-}
22

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