/bin/dash: Bad substitution

Question

I need to do a string manipuilation in shell script (/bin/dash):

#!/bin/sh

PORT="-p7777"
echo $PORT
echo ${PORT/p/P}

the last echo fails with Bad substitution. When I change shell to bash, it works:

#!/bin/bash

PORT="-p7777"
echo $PORT
echo ${PORT/p/P}

How can I implement the string substitution in dash ?

Answer 1

Using parameter expansion:

$ cat foo.sh
#!/bin/sh

PORT="-p7777"
echo $PORT
echo ${PORT:+-P${PORT#-p}}

PORT=""
echo $PORT
echo ${PORT:+-P${PORT#-p}}

Run it:

$ /bin/sh foo.sh
-p7777
-P7777

Update:

$ man dash:
- - 
${parameter#word}     Remove Smallest Prefix Pattern.

$ echo ${PORT#-p}
7777

$ man dash
- - 
${parameter:+word}    Use Alternative Value.

$ echo ${PORT:+-P${PORT#-p}}
-P7777