用Bash多次写入文件 [英] Writing to a file multiple times with Bash

问题描述

我正在创建一个bash脚本来自动化一些命令，并且在将错误检查写入同一文件时遇到了一些麻烦。

I am creating a bash script to automate some commands and I am having some trouble writing my error checking to the same file.

#!/bin/bash

touch ErrorLog.txt

bro-cut service < conn.log | sort | uniq -c > ProtocolHierarchy.txt
if [ $? -eq 0 ]; then
    echo -e "OK Protocol Hierarchy Created\n" > ErrorLog.txt
else
    echo -e "FAILED Creating Protocol Hierarchy\n" > ErrorLog.txt
fi

bro-cut id.orig_h < dns.log | sort | uniq -c > AllIPAddresses.txt

if [ $? -eq 0 ]; then
    echo -e "OK Created all IP Addresses\n" > ErrorLog.txt
else
    echo -e "FAILED Creating all IP Addresses\n" > ErrorLog.txt
fi

目标是拥有一个我可以打开的文件，并看到所有命令均有效或失败，当前文件如下所示：

The goal being to have a file I can open and see that all the commands worked or failed, currently the file looks like this

-e OK Created all IP Addresses

当我希望它看起来像这样

When I would like it to look like this

OK Protocol Hierarchy Created
OK Created all IP Addresses

我是bash脚本真的很新，因此任何提示将不胜感激！

I am really new to bash scripting so any tips would be greatly appreciated!

推荐答案

打开一次，然后多次写入该文件描述符。

Open it once, and write to that file descriptor multiple times.

# Open (creating or truncating) the output file (only once!)
exec 3>ErrorLog.txt

# Write a line to that already-open file
echo "something" >&3

# Write a second line to that already-open file
echo "something else" >&3

# Optional: close the output file (can also be implicit when the script exits)
exec 3>&-

另一个常见的习惯用法是使用>> 以附加模式打开，但是每行执行一次

The other common idiom is to open in append mode using >>, but doing that once per line is considerably less efficient.

# Open ErrorLog.txt, truncating if it exist, write one line, and close it
echo "something" >ErrorLog.txt

# Reopen ErrorLog.txt, write an additional line to the end, and close it again
echo "something else" >>ErrorLog.txt

---

将这种做法放入脚本中（并进行其他一些最佳实践的改进）如下所示：

---

Putting this practice to work in your script (and making some other best-practice improvements) looks like the following:

#!/bin/bash

# not related to file output, but to making sure we detect errors
# only works correctly if run with bash, not sh!
set -o pipefail ## set exit status based on whole pipeline, not just last command

# picking 3, since FD numbers 0-2 are reserved for stdin/stdout/stderr
exec 3>ErrorLog.txt

if bro-cut service <conn.log | sort | uniq -c >ProtocolHierarchy.txt; then
    echo "OK Protocol Hierarchy Created" >&3
else
    echo "FAILED Creating Protocol Hierarchy" >&3
fi

if bro-cut id.orig_h <dns.log | sort | uniq -c >AllIPAddresses.txt; then
    echo "OK Created all IP Addresses" >&3
else
    echo "FAILED Creating all IP Addresses" >&3
fi

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