Create 20150827 Linux or UNIX--Bash Read a File Line By Line.md

translated/tech/20150827 Linux or UNIX--Bash Read a File Line By Line.md

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+Linux/UNIX: 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 bash 的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:**
+
+1.对于 bash, ksh, zsh,和其他的 shells 语法如下 - 
+1. while read -r line; do COMMAND; done < input.file
+1.通过 -r 选项传递给红色的命令阻止反斜杠被解释。
+1.在 read 命令之前添加 IFS= option，来防止 leading/trailing 尾随的空白字符被分割 - 
+1. 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"
+
+在 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 <"$file"
+
+示例输出:
+
+![Fig.01: Bash shell scripting- read file line by line demo outputs](http://s0.cyberciti.org/uploads/faq/2011/01/Bash-Scripting-Read-File-line-by-line-demo.jpg)
+
+图01：Bash shell scripting- 读取文件并逐行输出文件
+
+**Bash Scripting: 逐行读取文本文件并创建为 pdf 文件**
+
+我的输入文件如下（faq.txt）:
+
+    4|http://www.cyberciti.biz/faq/mysql-user-creation/|Mysql User Creation: Setting Up a New MySQL User Account
+    4096|http://www.cyberciti.biz/faq/ksh-korn-shell/|What is UNIX / Linux Korn Shell?
+    4101|http://www.cyberciti.biz/faq/what-is-posix-shell/|What Is POSIX Shell?
+    17267|http://www.cyberciti.biz/faq/linux-check-battery-status/|Linux: Check Battery Status Command
+    17245|http://www.cyberciti.biz/faq/restarting-ntp-service-on-linux/|Linux Restart NTPD Service Command
+    17183|http://www.cyberciti.biz/faq/ubuntu-linux-determine-your-ip-address/|Ubuntu Linux: Determine Your IP Address
+    17172|http://www.cyberciti.biz/faq/determine-ip-address-of-linux-server/|HowTo: Determine an IP Address My Linux Server
+    16510|http://www.cyberciti.biz/faq/unix-linux-restart-php-service-command/|Linux / Unix: Restart PHP Service Command
+    8292|http://www.cyberciti.biz/faq/mounting-harddisks-in-freebsd-with-mount-command/|FreeBSD: Mount Hard Drive / Disk Command
+    8190|http://www.cyberciti.biz/faq/rebooting-solaris-unix-server/|Reboot a Solaris UNIX System
+
+我的 bash script:
+
+    #!/bin/bash
+    # Usage: Create pdf files from input (wrapper script)
+    # Author: Vivek Gite <Www.cyberciti.biz> under GPL v2.x+
+    #---------------------------------------------------------
+     
+    #Input file
+    _db="/tmp/wordpress/faq.txt"
+     
+    #Output location
+    o="/var/www/prviate/pdf/faq"
+     
+    _writer="~/bin/py/pdfwriter.py"
+     
+    # If file exists 
+    if [[ -f "$_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
+ 
+**提示：从 bash 的变量开始读取**
+
+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 中看到安装的包：
+
+    #!/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...
+
+
+    *** 不要忘了运行php5enmod并重新启动服务（httpd 或 php5-fpm） ***
+
+--------------------------------------------------------------------------------
+
+via: http://www.cyberciti.biz/faq/unix-howto-read-line-by-line-from-file/
+
+作者：[作者名][a]
+译者：[strugglingyouth](https://github.com/strugglingyouth)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](https://linux.cn/) 荣誉推出