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Random Talk on Random Thoughts

Used More Bash Utilities

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Background

Same as what has been written in my older post Using Xclip.

Drawback

Inputing the keyboard command for the paste action is, in my opinion, laborious.

Tools used

  1. find
  2. grep
  3. sed
  4. awk
  5. xargs

The find command

find . -path ./dir -prune -o -name '*.txt' -type f -print
find ./foo -exec wc {} \;
  • -path ./dir -prune -o: exclude the directory ./dir
  • -name '*.txt': match the name of the file
  • -type f: match files only, not directories
  • -print: print all matched paths
  • -exec {cmd} {} \;
    • execute one single command {cmd}, no pipes are allowed
    • {}: an instance of matched path
    • \;: terminator

I’ve found that if -type f goes before -path ./dir -prune -o, the path ./dir won’t be excluded. Don’t use ./, use .! on Mac.

Using -not -path ./dir option doesn’t work.

The grep command

  • -I: ignore binary files
  • -q . {}: match any characters and suppress output for faster execution

The sed command

  • -i .bak: edit file with backup extension .bak (Mac only, not in *nix)
  • -i '': no backup (Also Mac only)
  • sed 'p;s/foo/bar/': print original and replaced strings, separated by newline.

The awk command

The command awk '{ print $2 }' extracts the second column. For more examples, see the simple awk tutorial.

The xargs command

This is a very powerful command when combined with find. This utility reads from stdin and echos it.

  • no flags: all output joined into a single line
  • -n3: 3 space-delimited stdin in each line
  • xargs -n2 {cmd}: execute {cmd} {arg1} {arg2}, …, {cmd} {arg2n-1} {arg2n}.

Putting things together

Here’s some sample commands.

Find and replace for all text files under a path

find . -path ./.git -prune -o -type f -exec grep -Iq . {} \; -and \
-exec sed -i 's/foo/bar/g' {} \;

Ignore the .git folder, which is the Git repository, to avoid damaging it.

Find and replace substrings in path names

find . -path ./.git -prune -o -name "*foo*" -print | sed \
'p;s/foo/bar/g' | xargs -n2 mv

All instances of foo in path names are replaced with bar. Note that that -print option should be included. Otherwise, the path ./.git which is intended to be omitted will appear in the piped output and processed by sed, and then the terminal will throw the follow error message.

fatal: can not move directory into itself, source=.git, destination=.git/.git

Find and replace Git remote paths

$ git remote -v | awk '{ print $2 }' | head -1 | \
xargs git remote set-url origin
$ git remote -v
origin	https://github.com/VincentTam/StudentList1.git (fetch)
origin	https://github.com/VincentTam/StudentList1.git (push)
$ git remote -v | awk '{ print $2 }' | head -1 | sed \
's/StudentList1/StudentList4/' | xargs git remote set-url origin
$ git remote -v
origin	https://github.com/VincentTam/StudentList4.git (fetch)
origin	https://github.com/VincentTam/StudentList4.git (push)

(ADDED ON DEC 26TH, 2015)

The highlighting of grep after find

In Gnome Terminal, the grep command alone highlights the matched text in red by default. However, if it’s placed after find ... -exec, then the highlighting will be disabled. In order to enable it again, add the option --color=auto to grep.

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