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user10726006
Asked: 2018-12-03 02:23:03 +0800 CST

Use read line to iterate over variables

  • 772

I have the following files:

$ ls *.png | egrep -i "am|pm"
output-0 11.42.30 AM.png
output-0 5.10.12 PM.png
....

I want to remove them but get this error:

$ ls *.png | egrep -i "am|pm" | while read line; do rm "$line"; done
rm: cannot remove ''$'\033''[0m'$'\033''[01;35moutput-0 11.42.30 AM.png'$'\033''[0m': No such file or directory
rm: cannot remove ''$'\033''[01;35moutput-0 5.10.12 PM.png'$'\033''[0m': No such file or directory
rm: cannot remove ''$'\033''[01;35moutput-1 11.42.30 AM.png'$'\033''[0m': No such file or directory

What's the problem with my codes?

command-line bash ls

2 Answers

  1. Best Answer

    ls is risky in scripts and command lines. One problem is what is described in a comment by @PerlDuck, ANSI escape sequences for colour output. I would recommend another approach with find

    • Create test files

      touch 'output-0 11.42.30 AM.png' 'output-0 5.10.12 PM.png' asdf.png

    • Check that the findcommand line finds the files that you expect it to find

      find . -type f -iname "*[ap]m*.png"

      and do it

      find . -type f -iname "*[ap]m*.png" -delete

      If you don't want to search into subdirectories, add -maxdepth 1

      find . -maxdepth 1 -type f -iname "*[ap]m*.png" -delete

    • Check the result

      ls

      Files with am, pm, AM, PM in the name should be deleted but asdf.png is not deleted.

    • 9

  2. If you really want to use a while read loop in that way, then use a shell glob and printf with null delimiters e.g.

    printf '%s\0' *.png | grep -zEi 'am|pm' | while IFS= read -r -d '' line; do echo "$line"; done

    However, there are several ways to get bash to expand to a list of the files to be deleted directly - without the need to pipe to grep and while:

    1. using simple shell globs

      rm -- *[ap]m.png *[AP]M.png

      or - if you don't mind matching a .PNG extension as well - making use of the nocaseglob option

      shopt -s nocaseglob
rm -- *[ap]m.png

    2. using extended globs

      shopt -s extglob
rm -- *@(AM|PM).png *@(am|pm).png

    or

        shopt -s extglob nocaseglob
    rm -- *@(am|pm).png

    The -- marks the end of options, just in case there are filenames that begin with a hyphen - you can use a pattern with an explicit directory prefix like ./*(am|pm) instead if you prefer.

    Add the -i or -I option if you want to review the file names interactively before deletion.

    • 6