Question

I have a string variable $LIBRARIES="abc.so.1 def.so.1 hij.so.3.1" and I want to replace all the .so such that they look like this:

"abc.so* def.so* hij.so*" 

How can I do this? I tried NEW_LIBRARIES=${LIBRARIES//.so*/.so$star} but it doesn’t work. How can I tell it to end on whitespace?

Answer 1

This should do it:

LIBRARIES="abc.so.1 def.so.1 hij.so.3.1"
NEW_ALL_LIBRARIES=$(sed 's/\.so[^ ]*/\.so\*/g' <<< "$LIBRARIES")
echo "$NEW_ALL_LIBRARIES"

Output:

abc.so* def.so* hij.so*

Explanation:

• LIBRARIES="...": When assigning a string to a variable, the variable is not prefixed with $
• NEW_ALL_LIBRARIES=$(...): The $(...) notation is called command subsitution; basically it spawns a new subshell to run whatever commands contained within, then returns the output to this new subshell’s stdout (and here saving it to NEW_ALL_LIBRARIES).
• sed: invoke sed, the Streaming EDitor tool
• 's/\.so[^ ]*/\.so\*/g': Use regular expressions (regex) to match patterns and substitute. Let’s break this syntax down a bit further:
  • s/ “substitute”; For example: s/A/B/g replaces all occurrences of A with B
  • \.so[^ ]*/: Match any patterns that start with .so, and the [^ ]* part means “followed by zero or more non-space characters”
  • \.so\*/: Replace that with literally .so*
  • Some symbols such as [, ], . and * have special meaning in regex, so if you mean to use them literally, you just “escape” them by prefixing a \
  • g: Do so for all occurrences, not just the first.
• <<< "$LIBRARIES": the <<< notation is called herestring: in this context it accomplishes the same thing as echo "$LIBRARIES" | sed ..., but it saves a subshell.