rm fails to delete files by wildcard from a script, but works from a shell prompt

Question

I\'ve run into a really silly problem with a Linux shell script. I want to delete all files with the extension \".bz2\" in a directory. In the script I call

rm \         


        

Answer 1

Just to expand on this a bit, bash has fairly complicated rules for dealing with metacharacters in quotes. In general

• almost nothing is interpreted in single-quotes:

   echo '$foo/*.c'                  => $foo/*.c
   echo '\\*'                       => \\*
  

• shell substitution is done inside double quotes, but file metacharacters aren't expanded:

   FOO=hello; echo "$foo/*.c"       => hello/*.c
  

• everything inside backquotes is passed to the subshell which interprets them. A shell variable that is not exported doesn't get defined in the subshell. So, the first command echoes blank, but the second and third echo "bye":

  BAR=bye echo `echo $BAR`
  BAR=bye; echo `echo $BAR`
  export BAR=bye; echo `echo $BAR`
  

(And getting this to print the way you want it in SO takes several tries is apparently impossible...)