Bash doesn’t parse quotes when converting a string to arguments

by

The reason this happens is because of the order in which the shell parses the command line: it parses (and removes) quotes and escapes, then replaces variable values. By the time $test gets replaced with One "This is two" Three, it’s too late for the quotes to have their intended effect.

The simple (but dangerous) way to do this is by adding another level of parsing with eval:

$ test="One "This is two" Three"
$ eval "set -- $test"
$ echo "$2"
This is two

(Note that the quotes in the echo command are not necessary, but are a good general practice.)

The reason I say this is dangerous is that it doesn’t just go back and reparse for quoted strings, it goes back and reparses everything, maybe including things you didn’t want interpreted like command substitutions. Suppose you had set 

$ test="One `rm /some/important/file` Three"

…eval will actually run the rm command. So if you can’t count on the contents of $test to be “safe”, do not use this construct.

BTW, the right way to do this sort of thing is with an array:

$ test=(One "This is two" Three)
$ set -- "${test[@]}"
$ echo "$2"
This is two

Unfortunately, this requires control of how the variable is created.

More Related Contents:

  1. How to check if a string contains a substring in Bash
  2. How to compare strings in Bash
  3. How to use sed/grep to extract text between two words?
  4. How to trim whitespace from a Bash variable?
  5. Getting “command not found” error while comparing two strings in Bash
  6. How do I use variables in single quoted strings?
  7. How to get a variable value if variable name is stored as string?
  8. Extract substring in Bash
  9. In Bash, how can I check if a string begins with some value?
  10. How do I remove the file suffix and path portion from a path string in Bash?
  11. Get string after character [duplicate]
  12. Test whether string is a valid integer
  13. How to test if string exists in file with Bash?
  14. Replacing some characters in a string with another character
  15. Bash: Split string into character array
  16. How to return a string value from a Bash function
  17. Multi-line string with extra space (preserved indentation)
  18. Extract part of a string using bash/cut/split
  19. How can I compare a string to multiple correct values in Bash?
  20. Convert R vector to string vector of 1 element [duplicate]
  21. Shell script – remove first and last quote (“) from a variable
  22. How to echo “$x_$y” in Bash script?
  23. Why do I get “/bin/sh: Argument list too long” when passing quoted arguments?
  24. Convert specified column in a multi-line string into single comma-separated line
  25. bash : Bad Substitution
  26. Bash: manipulating with strings (percent sign)
  27. Test for empty string with X”” [duplicate]
  28. Split bash string by newline characters
  29. converting datetime string to POSIXct date/time format in R
  30. Python: most idiomatic way to convert None to empty string?

Leave a Comment