Mike Gerwitz

Activist for User Freedom

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#!/bin/bash
# Bash alternative to external cat call
#
#  Copyright (C) 2014 Mike Gerwitz
#
#  This file is part of pkgsh.
#
#  pkgsh is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# N.B. While this shell implementation may be faster for most use cases, the
# external binary will likely be much faster for large streams.
#
# This also contains some convenience functions that are not part of
# GNU coreutils.
##

[ -z $__PKGSH_INC_COREUTILS_CAT ] || return
__PKGSH_INC_COREUTILS_CAT=1


##
# Echo characters from stdin up to (but not including) the provided
# delimiter
cat-until()
{
  local -r delim="${1?Missing terminating delimiter}"
  local -r file="${2:-/dev/stdin}"

  read -rd "$delim" < "$file"
  local -ri result=$?

  echo -n "$REPLY"
  return $result
}


##
# Echo characters from stdin up to and including the provided delimiter
cat-until-incl()
{
  # `cat-until` will validate
  local -r delim="$1"
  cat-until "$@" \
    && echo -n "$delim"
}


##
# Proxies to either the shell implementation of cat or the system binary,
# depending on support
cat()
{
  [[ "$1" =~ ^-[^-\ ] ]] \
    && command cat "$@" \
    || quickcat "$@"
}


##
# Limited implementation of `cat` for performance
#
# TODO: The proper research has not yet gone into optimizing this; this is
# just an initial implementation to get things going. I will be addressing
# this shortly.
#
# TODO: Exit status.
quickcat()
{
  local in="${1:-/dev/stdin}"
  [ "$in" == - ] && in=/dev/stdin
  readonly in

  while true; do
    IFS= read -r || {
      echo -n "$REPLY"
      break
    }

    echo "$REPLY"
  done < "$in"

  if shift && [ $# -ne 0 ]; then
    quickcat "$@"
  fi
}