Super User is a question and answer site for computer enthusiasts and power users. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am checking a bash script which contains something like: export PATH=${PATH:+$PATH:}/usr/bin I assume it has same output as export PATH=$PATH:/usr/bin. I did a echo ${PATH:+$PATH:} it just output the value of $PATH plus a ':'. but if I modify it to ${PSOMETHING:+$PATH:}, it outputs nothing.

my question what's the different between using $PATH: and ${PATH:+$PATH:}? any benefit? how to understand the syntax?

share|improve this question
up vote 4 down vote accepted

See Parameter Expansion in man bash:

${parameter:+word}

Use Alternate Value. If parameter is null or unset, nothing is substituted, other- wise the expansion of word is substituted.

share|improve this answer
    
I just found it on tldp.org/LDP/abs/html/parameter-substitution.html thanks anyways – Fivesheep Nov 4 '12 at 7:56

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .