TranslateProject/published/201508/20150827 Linux or UNIX--Bash Read a File Line By Line.md
2015-08-31 23:46:47 +08:00

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Bash 下如何逐行读取一个文件
================================================================================
在 Linux 或类 UNIX 系统下如何使用 KSH 或 BASH shell 逐行读取一个文件?
在 Linux、OSX、 *BSD 或者类 Unix 系统下你可以使用 while..do..done 的 bash 循环来逐行读取一个文件。
###在 Bash Unix 或者 Linux shell 中逐行读取一个文件的语法
对于 bash、ksh、 zsh 和其他的 shells 语法如下
while read -r line; do COMMAND; done < input.file
通过 -r 选项传递给 read 命令以防止阻止解释其中的反斜杠转义符
read 命令之前添加 `IFS=` 选项来防止首尾的空白字符被去掉
while IFS= read -r line; do COMMAND_on $line; done < input.file
这是更适合人类阅读的语法:
#!/bin/bash
input="/path/to/txt/file"
while IFS= read -r var
do
echo "$var"
done < "$input"
**示例**
下面是一些例子:
#!/bin/ksh
file="/home/vivek/data.txt"
while IFS= read line
do
# display $line or do somthing with $line
echo "$line"
done <"$file"
bash shell 中相同的例子:
#!/bin/bash
file="/home/vivek/data.txt"
while IFS= read -r line
do
# display $line or do somthing with $line
printf '%s\n' "$line"
done <"$file"
你还可以看看这个更好的:
#!/bin/bash
file="/etc/passwd"
while IFS=: read -r f1 f2 f3 f4 f5 f6 f7
do
# display fields using f1, f2,..,f7
printf 'Username: %s, Shell: %s, Home Dir: %s\n' "$f1" "$f7" "$f6"
done <"$file"
示例输出:
![Fig.01: Bash shell scripting- read file line by line demo outputs](http://s0.cyberciti.org/uploads/faq/2011/01/Bash-Scripting-Read-File-line-by-line-demo.jpg)
*图01Bash 脚本:读取文件并逐行输出文件*
###Bash 脚本:逐行读取文本文件并创建为 pdf 文件
我的输入文件如下faq.txt:
4|http://www.cyberciti.biz/faq/mysql-user-creation/|Mysql User Creation: Setting Up a New MySQL User Account
4096|http://www.cyberciti.biz/faq/ksh-korn-shell/|What is UNIX / Linux Korn Shell?
4101|http://www.cyberciti.biz/faq/what-is-posix-shell/|What Is POSIX Shell?
17267|http://www.cyberciti.biz/faq/linux-check-battery-status/|Linux: Check Battery Status Command
17245|http://www.cyberciti.biz/faq/restarting-ntp-service-on-linux/|Linux Restart NTPD Service Command
17183|http://www.cyberciti.biz/faq/ubuntu-linux-determine-your-ip-address/|Ubuntu Linux: Determine Your IP Address
17172|http://www.cyberciti.biz/faq/determine-ip-address-of-linux-server/|HowTo: Determine an IP Address My Linux Server
16510|http://www.cyberciti.biz/faq/unix-linux-restart-php-service-command/|Linux / Unix: Restart PHP Service Command
8292|http://www.cyberciti.biz/faq/mounting-harddisks-in-freebsd-with-mount-command/|FreeBSD: Mount Hard Drive / Disk Command
8190|http://www.cyberciti.biz/faq/rebooting-solaris-unix-server/|Reboot a Solaris UNIX System
我的 bash 脚本:
#!/bin/bash
# Usage: Create pdf files from input (wrapper script)
# Author: Vivek Gite <Www.cyberciti.biz> under GPL v2.x+
#---------------------------------------------------------
#Input file
_db="/tmp/wordpress/faq.txt"
#Output location
o="/var/www/prviate/pdf/faq"
_writer="~/bin/py/pdfwriter.py"
# If file exists
if [[ -f "$_db" ]]
then
# read it
while IFS='|' read -r pdfid pdfurl pdftitle
do
local pdf="$o/$pdfid.pdf"
echo "Creating $pdf file ..."
#Genrate pdf file
$_writer --quiet --footer-spacing 2 \
--footer-left "nixCraft is GIT UL++++ W+++ C++++ M+ e+++ d-" \
--footer-right "Page [page] of [toPage]" --footer-line \
--footer-font-size 7 --print-media-type "$pdfurl" "$pdf"
done <"$_db"
fi
###技巧:从 bash 变量中读取
让我们看看如何在 Debian 或者 Ubuntu Linux 下列出所有安装过的 php 包,请输入:
# 我将输出内容赋值到一个变量名为 $list中 #
list=$(dpkg --list php\* | awk '/ii/{print $2}')
printf '%s\n' "$list"
示例输出:
php-pear
php5-cli
php5-common
php5-fpm
php5-gd
php5-json
php5-memcache
php5-mysql
php5-readline
php5-suhosin-extension
你现在可以从 $list 中看到它们,并安装这些包:
#!/bin/bash
# BASH can iterate over $list variable using a "here string" #
while IFS= read -r pkg
do
printf 'Installing php package %s...\n' "$pkg"
/usr/bin/apt-get -qq install $pkg
done <<< "$list"
printf '*** Do not forget to run php5enmod and restart the server (httpd or php5-fpm) ***\n'
示例输出:
Installing php package php-pear...
Installing php package php5-cli...
Installing php package php5-common...
Installing php package php5-fpm...
Installing php package php5-gd...
Installing php package php5-json...
Installing php package php5-memcache...
Installing php package php5-mysql...
Installing php package php5-readline...
Installing php package php5-suhosin-extension...
*** Do not forget to run php5enmod and restart the server (httpd or php5-fpm) ***
--------------------------------------------------------------------------------
via: http://www.cyberciti.biz/faq/unix-howto-read-line-by-line-from-file/
作者: VIVEK GIT
译者:[strugglingyouth](https://github.com/strugglingyouth)
校对:[wxy](https://github.com/wxy)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译,[Linux中国](https://linux.cn/) 荣誉推出