SHELL下十二种读文件的方法及运行效率

#!/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

结果:

$ ./read_file.sh mylist.txt

Starting File Processing of each Method

Method 1:
function while_read_LINE
    0.58s real     0.20s user     0.48s system

Method 2:
function while_read_LINE_bottom
    0.03s real     0.00s user     0.03s system

Method 3:
function while_line_LINE_bottom
    4.41s real     0.17s user     0.40s system

Method 4:
function cat_while_LINE_line
    4.55s real     6.94s user     3.21s system

Method 5:
function while_line_LINE
    4.48s real     6.53s user     3.29s system

Method 6:
function while_LINE_line_bottom
    4.28s real     0.23s user     0.40s system

Method 7:
function while_LINE_line_cmdsub2
    4.57s real     6.73s user     3.10s system

Method 8:
function while_LINE_line_bottom_cmdsub2
    4.47s real     0.17s user     0.40s system

Method 9:
function while_read_LINE_FD
    0.02s real     0.01s user     0.01s system

Method 10:
function while_LINE_line_FD
    4.30s real     0.21s user     0.49s system

Method 11:
function while_LINE_line_cmdsub2_FD
    4.37s real     0.10s user     0.53s system

Method 12:
function while_line_LINE_FD
    4.25s real     0.10s user     0.49s system