I don\u2019t do much shell scripting, but every once in a while I use it to automate things. I was playing around with bash today and thought this might interest others.<\/p>\n
Define an array variable
\n$ servers=(server purple yellow dan);
\n$ echo $servers
\nserver<\/p>\n
Redefine it.
\n$ servers=(firstserver server purple yellow dan);
\n$ echo $servers
\nfirstserver<\/p>\n
That\u2019s not what I want. So how do we access the values? Let\u2019s try a for loop.
\n$ for name in $servers; do echo $name; done;
\n$ echo $servers
\nfirstserver<\/p>\n
Well that didn\u2019t do it. Let\u2019s try to access the second value with array notation.
\n$ for name in $servers; do echo $servers[1]; done;
\nfirstserver[1]<\/p>\n
If you look carefully at this you\u2019ll notice that what is happening is that you are concatenating the return value from $server with [1]. Try it again with this line.<\/p>\n
$ for name in $servers; do echo $servers[a]; done;
\nfirstserver[a]<\/p>\n
And again.
\n$ for name in $servers; do echo $servers.a; done;
\nfirstserver.a<\/p>\n
As long as you use a character that is not a valid part of a variable name, you get concatenation.
\ne.g. don\u2019t use an alphanumeric.
\n$ for name in $servers; do echo $serversabc; done;<\/p>\n
There is no variable called serverabc, so you get a blank line.<\/p>\n
It turns out that bash has weird syntax for working with variables.
\n$ echo ${servers[2]}
\npurple<\/p>\n
Add another value.
\n$ servers[5]=finalvalue
\n$ echo ${servers[5]}
\nfinalvalue<\/p>\n
So how about we separate out the loop variable like this?
\n$ for name in $servers; do echo $servers${name}; done;
\nfirstserverfirstserver<\/p>\n
Well, we\u2019re getting warmer.
\n$ for name in $servers; do echo $name; done;
\nfirstserver<\/p>\n
This is getting frustrating. Let\u2019s back up and try just listing a bunch of stuff in a list.
\n$ for name in firstserver server purple yellow dan finalvalue; do echo $name; done;
\nfirstserver
\nserver
\npurple
\nyellow
\ndan
\nfinalvalue<\/p>\n
So we can make a for loop iterate through items, but the normal way of accessing elements of an array doesn\u2019t work in bash. It turns out that you need special syntax.<\/p>\n
$ echo ${servers[@]}
\nfirstserver server purple yellow finalvalue finalvalue<\/p>\n
And to loop through everything like we wanted to do at the start.
\n$ for name in ${servers[@]}; do echo $name; done;
\nfirstserver
\nserver
\npurple
\nyellow
\ndan
\nfinal value<\/p>\n
That wasn\u2019t so hard was it?<\/p>\n","protected":false},"excerpt":{"rendered":"
I don\u2019t do much shell scripting, but every once in a while I use it to automate things. I was playing around with bash today and thought this might interest others. Define an array variable $ servers=(server purple yellow dan); $ echo $servers server Redefine it. $ servers=(firstserver server purple yellow dan); $ echo $servers … Continue reading for loops in bash<\/span><\/a><\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-1884","post","type-post","status-publish","format-standard","hentry","category-coding"],"_links":{"self":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/posts\/1884","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1884"}],"version-history":[{"count":0,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=\/wp\/v2\/posts\/1884\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1884"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1884"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.wellgolly.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1884"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}