用bash指令碼讀檔案的方法有很多。請看第一部分,我使用了while迴圈及其後的管道命令(|)(cat $FILE | while read line; do … ),並在迴圈當中遞增 i 的值,最後,我得到了非我所想的 i 。主要的原因是,管道命令會發起子shell來讀取檔案,而任何在(子shell的)while迴圈中的操作(例如 i ++),都會隨著子shell的結束而丟失。
而第二種,也是最壞的一種,其最明顯的錯誤就是在讀檔案的過程中使用了for迴圈(for fileline in $(cat $FILE);do ..),這樣每列印一個單詞就換一次行,因為for迴圈使用空格作為預設的IFS。
完美的方法,即第三種的while迴圈(while read line;do …. done < $FILE) 是最合適且最簡單的一行行地讀檔案的方法。請看以下例子。
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Input: $ cat sample.txt This is sample file This is normal text file Source: $ cat readfile.sh #!/bin/bash i=1; FILE=sample.txt # Wrong way to read the file. # This may cause problem, check the value of 'i' at the end of the loop echo "###############################" cat $FILE | while read line; do echo "Line # $i: $line" ((i++)) done echo "Total number of lines in file: $i" # The worst way to read file. echo "###############################" for fileline in $(cat $FILE);do echo $fileline done # This is correct way to read file. echo "################################" k=1 while read line;do echo "Line # $k: $line" ((k++)) done < $FILE echo "Total number of lines in file: $k" Output: $ ./readfile.sh ############################### Line # 1: This is sample file Line # 2: This is normal text file Total number of lines in file: 1 ############################### This is sample file This is normal text file ################################ Line # 1: This is sample file Line # 2: This is normal text file Total number of lines in file: 3 |