9.5 Build Strings with { }

I've been finding more and more uses for the {} pattern-expansion characters in csh, tcsh, and bash. (Other shells can use {}, too; see article 15.3.) They're similar to *, ?, and [] (15.2), but they don't match filenames the way that *, ?, and [] do. You can give them arbitrary text (not just filenames) to expand - that "expand-anything" ability is what makes them so useful.

Here are some examples to get you thinking:

• To fix a typo in a filename (change fixbold5.c to fixbold6.c):

  % mv fixbold{5,6}.c

  An easy way to see what the shell does with {} is by adding echo (8.6) before the mv:

  % echo mv fixbold{5,6}.c
  mv fixbold5.c fixbold6.c

• To copy filename to filename.bak in one easy step:

  % cp filename{,.bak}

• To print files from other directory(s) without retyping the whole pathname:

  % lpr /usr3/hannah/training/{ed,vi,mail}/lab.{ms,out}

  That would give lpr (43.2) all of these files:

  /usr3/hannah/training/ed/lab.ms
  /usr3/hannah/training/ed/lab.out
  /usr3/hannah/training/vi/lab.ms
  /usr3/hannah/training/vi/lab.out
  /usr3/hannah/training/mail/lab.ms
  /usr3/hannah/training/mail/lab.out

  ...in one fell swoop!

• To edit ten new files that don't exist yet:

  % vi /usr/foo/file{a,b,c,d,e,f,g,h,i,j}

  That would make /usr/foo/filea, /usr/foo/fileb, ... /usr/foo/filej. Because the files don't exist before the command starts, the wildcard vi /usr/foo/file[a-j] would not work (9.4).

• An easy way to step through three-digit numbers 000, 001, ..., 009, 010, 011, ..., 099, 100, 101, ... 299 is:

  foreach	foreach n ({0,1,2}{0,1,2,3,4,5,6,7,8,9}{0,1,2,3,4,5,6,7,8,9}) ...Do whatever with the number $n... end

  Yes, csh also has built-in arithmetic, but its @ operator (47.4) can't make numbers with leading zeros. This nice trick shows that the {} operators are good for more than just filenames.

• To create sets of subdirectories:

  % mkdir man
  % mkdir man/{man,cat}{1,2,3,4,5,6,7,8}
  % ls -F man
  cat1/   cat3/   cat5/   cat7/   man1/   man3/   man5/   man7/
  cat2/   cat4/   cat6/   cat8/   man2/   man4/   man6/   man8/

• To print ten copies of the file project_report (if your lpr (43.2) command doesn't have a -#10 option):

  % lpr project_repor{t,t,t,t,t,t,t,t,t,t}