shell下12种读文件的方法

#!/usr/bin/ksh

#

# SCRIPT: 12_ways_to_parse.ksh.ksh

#

#

# REV: 1.2.A

#

# PURPOSE:  This script shows the different ways of reading

#       a file line by line.  Again there is not just one way

#       to read a file line by line and some are faster than

#       others and some are more intuitive than others.

#

# REV LIST:

#

#       03/15/2002 - Randy Michael

#       Set each of the while loops up as functions and the timing

#       of each function to see which one is the fastest.

#

#######################################################################

#

#       NOTE: To output the timing to a file use the following syntax:

#

#          12_ways_to_parse.ksh file_to_process  > output_file_name 2>&1

#

#       The actaul timing data is sent to standard error, file

#       descriptor (2), and the function name header is sent

#       to standard output, file descriptor (1).

#

#######################################################################

#

# set -n  # Uncomment to check command syntax without any execution

# set -x  # Uncomment to debug this script

#

FILENAME="$1"

TIMEFILE="/tmp/loopfile.out"

>$TIMEFILE

THIS_SCRIPT=$(basename $0)

######################################

function usage

{

echo "\nUSAGE: $THIS_SCRIPT  file_to_process\n"

echo "OR - To send the output to a file use: "

echo "\n$THIS_SCRIPT  file_to_process  > output_file_name 2>&1 \n"

exit 1

}

######################################

function while_read_LINE

{

cat $FILENAME | while read LINE

do

echo "$LINE"

:

done

}

######################################

function while_read_LINE_bottom

{

while read LINE

do

echo "$LINE"

:

done < $FILENAME

}

######################################

function while_line_LINE_bottom

{

while line LINE

do

echo $LINE

:

done < $FILENAME

}

######################################

function cat_while_LINE_line

{

cat $FILENAME | while LINE=`line`

do

echo "$LINE"

:

done

}

######################################

function while_line_LINE

{

cat $FILENAME | while line LINE

do

echo "$LINE"

:

done

}

######################################

function while_LINE_line_bottom

{

while LINE=`line`

do

echo "$LINE"

:

done < $FILENAME

}

######################################

function while_LINE_line_cmdsub2

{

cat $FILENAME | while LINE=$(line)

do

echo "$LINE"

:

done

}

######################################

function while_LINE_line_bottom_cmdsub2

{

while LINE=$(line)

do

echo "$LINE"

:

done < $FILENAME

}

######################################

function while_read_LINE_FD

{

exec 3<&0

exec 0< $FILENAME

while read LINE

do

echo "$LINE"

:

done

exec 0<&3

}

######################################

function while_LINE_line_FD

{

exec 3<&0

exec 0< $FILENAME

while LINE=`line`

do

echo "$LINE"

:

done

exec 0<&3

}

######################################

function while_LINE_line_cmdsub2_FD

{

exec 3<&0

exec 0< $FILENAME

while LINE=$(line)

do

print "$LINE"

:

done

exec 0<&3

}

######################################

function while_line_LINE_FD

{

exec 3<&0

exec 0< $FILENAME

while line LINE

do

echo "$LINE"

:

done

exec 0<&3

}

######################################

########### START OF MAIN ############

######################################

# Test the Input

# Looking for exactly one parameter

(( $# == 1 )) || usage

# Does the file exist as a regular file?

[[ -f $1 ]] || usage

echo "\nStarting File Processing of each Method\n"

echo "Method 1:"

echo "\nfunction while_read_LINE\n" >> $TIMEFILE

echo "function while_read_LINE"

time while_read_LINE >> $TIMEFILE

echo "\nMethod 2:"

echo "\nfunction while_read_LINE_bottom\n" >> $TIMEFILE

echo "function while_read_LINE_bottom"

time while_read_LINE_bottom >> $TIMEFILE

echo "\nMethod 3:"

echo "\nfunction while_line_LINE_bottom\n" >> $TIMEFILE

echo "function while_line_LINE_bottom"

time while_line_LINE_bottom >> $TIMEFILE

echo "\nMethod 4:"

echo "\nfunction cat_while_LINE_line\n" >> $TIMEFILE

echo "function cat_while_LINE_line"

time cat_while_LINE_line >> $TIMEFILE

echo "\nMethod 5:"

echo "\nfunction while_line_LINE\n" >> $TIMEFILE

echo "function while_line_LINE"

time while_line_LINE >> $TIMEFILE

echo "\nMethod 6:"

echo "\nfunction while_LINE_line_bottom\n" >> $TIMEFILE

echo "function while_LINE_line_bottom"

time while_LINE_line_bottom >> $TIMEFILE

echo "\nMethod 7:"

echo "\nfunction while_LINE_line_cmdsub2\n" >> $TIMEFILE

echo "function while_LINE_line_cmdsub2"

time while_LINE_line_cmdsub2 >> $TIMEFILE

echo "\nMethod 8:"

echo "\nfunction while_LINE_line_bottom_cmdsub2\n" >> $TIMEFILE

echo "function while_LINE_line_bottom_cmdsub2"

time while_LINE_line_bottom_cmdsub2 >> $TIMEFILE

echo "\nMethod 9:"

echo "\nfunction while_read_LINE_FD\n" >> $TIMEFILE

echo "function while_read_LINE_FD"

time while_read_LINE_FD >> $TIMEFILE

echo "\nMethod 10:"

echo "\nfunction while_LINE_line_FD\n" >> $TIMEFILE

echo "function while_LINE_line_FD"

time while_LINE_line_FD >> $TIMEFILE

echo "\nMethod 11:"

echo "\nfunction while_LINE_line_cmdsub2_FD\n" >> $TIMEFILE

echo "function while_LINE_line_cmdsub2_FD"

time while_LINE_line_cmdsub2_FD >> $TIMEFILE

echo "\nMethod 12:"

echo "\nfunction while_line_LINE_FD\n" >> $TIMEFILE

echo "function while_line_LINE_FD"

time while_line_LINE_FD >> $TIMEFILE