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1.4 Notes ¶

When using MBFL we want to be aware of the following:

• When in doubt about how some functions work: we should take a look at the source code. When doing this we must remember that: there is no word splitting when performing variable assignment; so there is no need to use double quotes in the following cases:

  alpha=$beta
  alpha=${beta:1:3}
  alpha=${beta:-$gamma}
  alpha=${#beta}
  

  There is also no word splitting when evaluating the WORD in the case statement; so there is no need to use double quotes in the following case:

  case $WORD in
    ...
  esac
  

• Some functions take a variable name as argument and store in the referenced variable some value; to avoid name collision without using the preprocessor: select a name that starts with p_. It is guaranteed that MBFL never uses variables with name starting with such a prefix.
• The read built in does word splitting on the text it reads, even when there is a single output variable. We can verify it with:

  printf '\tciao\n' | {
      read line
      echo line was "'$line'"
  }
  -| line was 'ciao'
  

  we see that the initial tabulation character has been stripped, because it is a character in the default value of IFS. Word splitting does not happen when we set IFS to the empty string:

  printf '\tciao\n' | {
      IFS= read line
      echo line was "'$line'"
  }
  -| line was '        ciao'
  

  To avoid the mutation of text read with read, MBFL always sets IFS to the empty string in the environment in which read is evaluated. This happens in functions like mbfl_read_maybe_null() and mbfl_dialog_ask_password(); notice, though, that these functions do not mutate the IFS value in the environment of the caller.