shell - 如何使用fish预先添加文件

Question

我看到 bash 有几个很好的答案甚至 zsh (即 Here )。虽然我找不到合适的 fish .
是否有规范的或干净的将一个字符串或几行添加到现有文件中(就地)？类似于 cat "new text" >> test.txt为追加做。

Answer 1

作为fish 有意简化的一部分，它避免了zsh 中的语法糖。等效于 zsh-only 代码 <<< "to be prepended" < text.txt | sponge text.txt在 fish 是:

begin; echo "to be prepended"; cat test.txt; end | sponge test.txt

sponge是来自 moreutils 的工具包裹; fish 版本与 zsh 原始版本一样需要它。然而，你可以很容易地用一个函数替换它；考虑以下:

# note that this requires GNU chmod, though it works if you have it installed under a
# different name (f/e, installing "coreutils" on MacOS with nixpkgs, macports, etc),
# it tries to figure that out.
function copy_file_permissions -a srcfile destfile
  if command -v coreutils &>/dev/null  # works with Nixpkgs-installed coreutils on Mac
    coreutils --coreutils-prog=chmod --reference=$srcfile -- $destfile
  else if command -v gchmod &>/dev/null  # works w/ Homebrew coreutils on Mac
    gchmod --reference=$srcfile -- $destfile
  else
    # hope that just "chmod" is the GNU version, or --reference won't work
    chmod --reference=$srcfile -- $destfile
  end
end

function mysponge -a destname
  set tempfile (mktemp -t $destname.XXXXXX)
  if test -e $destname
    copy_file_permissions $destname $tempfile
  end
  cat >$tempfile
  mv -- $tempfile $destname
end

function prependString -a stringToPrepend outputName
  begin
    echo $stringToPrepend
    cat -- $outputName
  end | mysponge $outputName
end

prependString "First Line" out.txt
prependString "No I'm First" out.txt