how to echo a double backslash plus a variable (version number) like “\\hostname\release\1.02A01” by using sh?

问题

I want to echo a Windows shared folder address to users in a Linux shell script, the address are strings like this: \\hostname\release\1.02A01. and the last string(1.02A01) is a version number, it's changed each time when I run the script. I tried something like this in sh (not bash ), but it doesn't work:

version=$1 # version number are get from the parameter

repository="\\\hostname\release\$version"

echo $repository # I get this: \hostname\dir$version

Here are the two errors:

the double backslashes are not correct.
the version is not parsed correctly.

回答1:

1) In unix/linux sh, the backslash("\") has to be escaped/preceded with a backslash("\").
2) The string concatenation you are doing INSIDE quotes is LITERAL, if you want the value of $version, you have to put it OUTSIDE the closing quote.

I put this in a shell ( shell1 ) in centos linux and executed it under "sh":

sh-4.1# cat shell1
version=$1
repository="\\\\hostname\\release\\"$version
echo $repository

This is the output:

sh-4.1# ./shell1 1.02A01 <br>
\\hostname\release\1.02A01

回答2:

To avoid needing to escape the backslashes, use single quotes instead of double quotes.

repository='\\hostname\release\'"$version"

The double quotes are needed for $version to allow the parameter expansion to occur. Two quoted strings adjacent to each other like this are concatenated into one string.

回答3:

Ah the BASH escape trap.

Maybe try:

version=`echo $1`
repository='\''\hostname\release\'$version

Tested with:

~ $ cat stack

#!/bin/bash

string="1.02A01"
version=`echo $string`
repository='\''\hostname\release\'$version

echo $repository

~ $ bash stack

\\hostname\release\1.02A01

回答4:

Do not use echo to output text and use printf instead. The echo command has several portability issues and the printf function is much easier to use because it has a clear “print what I meant” part — the format string — with placeholders for text replacement.

repository="\\\\hostname\\release\\$version"
printf '%s\n' "$repository"

You should reserve the use of echo for the most simple bits of information, like tracing messages, or even not use it at all.

来源：https://stackoverflow.com/questions/25678262/how-to-echo-a-double-backslash-plus-a-variable-version-number-like-hostname

标签

Linux

shell

escaping