Command Substitution

• Run the command inside backquotes (`...`), replace that command with its output.
• Example: Print all files modified in past day:
  % lpr `find * -type f -mtime -1 -print`
  How does that work?
  1. Shell runs command in backquotes and collects its output:
     find * -type f -mtime -1 -print
     afile
     bfile
     subdir/cfile
  2. Shell runs "outer" command, substituting previous results:
     % lpr afile bfile subdir/cfile
     
• Example: edit all files whose text has the word "CAUTION":
  % vi `grep -l CAUTION *`
• Alternate syntax in bash: $(...)
  % vi $(grep -l CAUTION *)
• Alternate syntax makes nesting easier:
  % vi $(grep -l CAUTION $(find * -mtime -1 -print))