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Delete 20150827 Linux or UNIX--Bash Read a File Line By Line.md
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translation by strugglingyouth
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Linux/UNIX: Bash Read a File Line By Line
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================================================================================
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How do I read a file line by line under a Linux or UNIX-like system using KSH or BASH shell?
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You can use while..do..done bash loop to read file line by line on a Linux, OSX, *BSD, or Unix-like system.
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**Syntax to read file line by line on a Bash Unix & Linux shell:**
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1. The syntax is as follows for bash, ksh, zsh, and all other shells -
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1. while read -r line; do COMMAND; done < input.file
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1. The -r option passed to red command prevents backslash escapes from being interpreted.
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1. Add IFS= option before read command to prevent leading/trailing whitespace from being trimmed -
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1. while IFS= read -r line; do COMMAND_on $line; done < input.file
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Here is more human readable syntax for you:
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#!/bin/bash
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input="/path/to/txt/file"
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while IFS= read -r var
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do
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echo "$var"
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done < "$input"
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**Examples**
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Here are some examples:
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#!/bin/ksh
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file="/home/vivek/data.txt"
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while IFS= read line
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do
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# display $line or do somthing with $line
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echo "$line"
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done <"$file"
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The same example using bash shell:
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#!/bin/bash
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file="/home/vivek/data.txt"
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while IFS= read -r line
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do
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# display $line or do somthing with $line
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printf '%s\n' "$line"
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done <"$file"
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You can also read field wise:
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#!/bin/bash
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file="/etc/passwd"
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while IFS=: read -r f1 f2 f3 f4 f5 f6 f7
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do
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# display fields using f1, f2,..,f7
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printf 'Username: %s, Shell: %s, Home Dir: %s\n' "$f1" "$f7" "$f6"
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done <"$file"
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Sample outputs:
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Fig.01: Bash shell scripting- read file line by line demo outputs
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**Bash Scripting: Read text file line-by-line to create pdf files**
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My input file is as follows (faq.txt):
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4|http://www.cyberciti.biz/faq/mysql-user-creation/|Mysql User Creation: Setting Up a New MySQL User Account
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4096|http://www.cyberciti.biz/faq/ksh-korn-shell/|What is UNIX / Linux Korn Shell?
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4101|http://www.cyberciti.biz/faq/what-is-posix-shell/|What Is POSIX Shell?
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17267|http://www.cyberciti.biz/faq/linux-check-battery-status/|Linux: Check Battery Status Command
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17245|http://www.cyberciti.biz/faq/restarting-ntp-service-on-linux/|Linux Restart NTPD Service Command
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17183|http://www.cyberciti.biz/faq/ubuntu-linux-determine-your-ip-address/|Ubuntu Linux: Determine Your IP Address
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17172|http://www.cyberciti.biz/faq/determine-ip-address-of-linux-server/|HowTo: Determine an IP Address My Linux Server
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16510|http://www.cyberciti.biz/faq/unix-linux-restart-php-service-command/|Linux / Unix: Restart PHP Service Command
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8292|http://www.cyberciti.biz/faq/mounting-harddisks-in-freebsd-with-mount-command/|FreeBSD: Mount Hard Drive / Disk Command
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8190|http://www.cyberciti.biz/faq/rebooting-solaris-unix-server/|Reboot a Solaris UNIX System
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My bash script:
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#!/bin/bash
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# Usage: Create pdf files from input (wrapper script)
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# Author: Vivek Gite <Www.cyberciti.biz> under GPL v2.x+
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#---------------------------------------------------------
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#Input file
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_db="/tmp/wordpress/faq.txt"
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#Output location
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o="/var/www/prviate/pdf/faq"
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_writer="~/bin/py/pdfwriter.py"
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# If file exists
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if [[ -f "$_db" ]]
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then
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# read it
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while IFS='|' read -r pdfid pdfurl pdftitle
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do
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local pdf="$o/$pdfid.pdf"
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echo "Creating $pdf file ..."
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#Genrate pdf file
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$_writer --quiet --footer-spacing 2 \
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--footer-left "nixCraft is GIT UL++++ W+++ C++++ M+ e+++ d-" \
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--footer-right "Page [page] of [toPage]" --footer-line \
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--footer-font-size 7 --print-media-type "$pdfurl" "$pdf"
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done <"$_db"
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fi
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**Tip: Read from bash variable**
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Let us say you want a list of all installed php packages on a Debian or Ubuntu Linux, enter:
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# My input source is the contents of a variable called $list #
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list=$(dpkg --list php\* | awk '/ii/{print $2}')
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printf '%s\n' "$list"
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Sample outputs:
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php-pear
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php5-cli
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php5-common
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php5-fpm
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php5-gd
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php5-json
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php5-memcache
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php5-mysql
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php5-readline
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php5-suhosin-extension
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You can now read from $list and install the package:
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#!/bin/bash
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# BASH can iterate over $list variable using a "here string" #
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while IFS= read -r pkg
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do
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printf 'Installing php package %s...\n' "$pkg"
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/usr/bin/apt-get -qq install $pkg
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done <<< "$list"
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printf '*** Do not forget to run php5enmod and restart the server (httpd or php5-fpm) ***\n'
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Sample outputs:
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Installing php package php-pear...
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Installing php package php5-cli...
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Installing php package php5-common...
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Installing php package php5-fpm...
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Installing php package php5-gd...
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Installing php package php5-json...
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Installing php package php5-memcache...
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Installing php package php5-mysql...
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Installing php package php5-readline...
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Installing php package php5-suhosin-extension...
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*** Do not forget to run php5enmod and restart the server (httpd or php5-fpm) ***
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--------------------------------------------------------------------------------
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via: http://www.cyberciti.biz/faq/unix-howto-read-line-by-line-from-file/
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作者：[作者名][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](https://linux.cn/) 荣誉推出
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