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Saving Time on the Command Line
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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}
    
    

- JP


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