head-pos

实战Linux编程的原代码,希望对学驱动的人能有所帮助

#!/bin/sh
# When reading a specified number of lines, ensure that the output
# file pointer is positioned just after those lines.

if test "$VERBOSE" = yes; then
  set -x
  head --version
fi

pwd=`pwd`
tmp=head-pos.$$
trap 'status=$?; cd $pwd; rm -rf $tmp && exit $status' 0
trap '(exit $?); exit' 1 2 13 15

framework_failure=0
mkdir $tmp || framework_failure=1
cd $tmp || framework_failure=1
(echo a; echo b) > in || framework_failure=1

if test $framework_failure = 1; then
  echo "$0: failure in testing framework" 1>&2
  (exit 1); exit
fi

fail=0
(head -n 1 >/dev/null; cat) < in > out || fail=1
cat <<EOF > exp
b
EOF

cmp out exp || fail=1
test $fail = 1 && diff out exp 2> /dev/null

(exit $fail); exit