Posts Tagged 'bash'

Creating dummy (empty) files

For testing shell tips (linux and cygwin) it is often handy to

  • work a test directory
  • make some (tons of!) files
  • Ok, I suppose you can create directories (mkdir dirname). Now, you can use touch to create (empty) files:

    touch a b c d

    will create files a, b, c and d.

    To create 200 file starting their names with file_, followed with a number and ending with .img, do

    mkdir source
    cd source
    for ((num=0;num<200;num+=1)); do touch file_${num}.img ; done

    Now you can tests the shell tips (example).

    200 files made with touch command and a bash loop

    Batch renaming files

    Whether you are using linux (bash or shell) or cygwin, renaming a (large) set of files is really easy. Because renaming a file and changing its location is the same thing for linux and cygwin, you’ve got a large set of possibilities.

    First example. Say you have 200 files in a directory that must receive a prefix like new_. Here is what you can write from the prompt.

    for f in * ; do mv $f new_$f ; done

    and ALL files in the current directory have their names starting with new_ now.
    The star * tells to consider any file. For each file found, its name is stored in the variable f and the command mv $f new_$f is executed. The $f is replaced by each filename.
    Moving the files to another place is trivial. Say you have a directory named source and another named target, you can:

    cd source
    for f in * ; do mv $f ../target/new_$f ; done
    cd ..

    (you can use cp instead of mv to copy the original files to another named file).

    Second example. Now you want to change the file extension. It comes that bash lets you do some operations on the variables. For example, if f contains a string that ends with .img, say my_image.img, the instruction ${f%.img} would remove the extension .img from the end of the string (more manipulation in future posts). Renaming files ending with .img with .ida would be:

    for f in *.img ; do mv $f ${f%.img}.ida ; done

    More on files manipulation in future posts!