{"id":866,"date":"2020-12-05T20:28:15","date_gmt":"2020-12-05T18:28:15","guid":{"rendered":"https:\/\/www.bashpi.org\/?page_id=866"},"modified":"2021-04-13T10:09:38","modified_gmt":"2021-04-13T07:09:38","slug":"bash-arrays","status":"publish","type":"page","link":"https:\/\/www.bashpi.org\/?page_id=866","title":{"rendered":"Bash arrays"},"content":{"rendered":"\n

There are two types of arrays you can use – indexed and associative arrays.<\/p>\n\n\n\n

Start by declaring the arrays<\/strong><\/p>\n\n\n\n

$ declare -a indexed_array\n$ declare -A associative_array<\/pre>\n\n\n\n
Add values to arrays<\/strong> – note the possibility to add values to arrays with += operator.<\/p>\n\n\n\n
$ indexed_array[0]=\"value1\"\n$ indexed_array[1]=\"value2\"\n$ indexed_array[2]=\"value3\"\n$ indexed_array+=\"value4\"\n$ indexed_array+=\"value5\"\n\n$ associative_array[one]=\"value1\"\n$ associative_array[two]=\"value2\"\n$ associative_array[three]=\"value3\"\n\n# or add multiple values like this\n\n$ indexed_array=(value6 value7 value8)\n$ indexed_array+=(value4 value5)\n$ associative_array=([one]=value1 [two]=value2 [three]=value3)\n$ associative_array+=([four]=value4 [five]=value5)<\/pre>\n\n\n\n
Print out array values<\/strong><\/p>\n\n\n\n
$ echo ${indexed_array[@]}\n\n# or \n\n$ echo ${associative_array[*]}\n<\/pre>\n\n\n\n
Print out array indexes or keys<\/strong> – add ! before array name<\/p>\n\n\n\n
for index in \"${!indexed_array[@]}\"; do \n echo \"${index}\"\ndone\n\nfor key in \"${!associative_array[@]}\"; do\necho \"$key\"\ndone<\/pre>\n\n\n\n
Number of values in arrays<\/strong> – use # before array name<\/p>\n\n\n\n
echo \"indexed array contains ${#indexed_array[@]} values\"\necho \"associative_array array contains ${#associative_array[@]} values\"<\/pre>\n\n\n\n
Deleting values from an array<\/strong> – use unset<\/p>\n\n\n\n
unset indexed_array[2]\nunset associative_array[three]<\/pre>\n\n\n\n
Deleting entire array<\/strong> – useful if you play around with lost of data<\/p>\n\n\n\n
unset indexed_array\nunset associative_array<\/pre>\n\n\n\n
Read file into array <\/strong>– you don’t need to loop trough each line<\/p>\n\n\n\n
Use bash internal command readarray.  -t option removes trailing newline. More options look in man bash<\/code>. Following will read each line of file.txt into indexed array named indexed_array<\/em>.<\/p>\n\n\n\n
readarray -t indexed_array < file.txt<\/pre>\n\n\n\n
Add command output into an array<\/strong> – same thing, you don’t need loop<\/p>\n\n\n\n
Use bash internal command readarray. -t option removes trailing newline. More options look in man bash<\/code>. Following will read each line of ps -ef into indexed array named indexed_array<\/em>. Note the double < < separated with space. This is called process substitution<\/a>. This feeds command output into stdin of the readarray command. NB! dont leave space between last < and the brackets. <\/p>\n\n\n\n
readarray -t indexed_array < <(ps -ef)<\/pre>\n\n\n\n
<\/p>\n\n\n\n
If you found this useful, say thanks, click on some banners or donate<\/a>, I can always use some beer money.<\/p>\n","protected":false},"excerpt":{"rendered":"
There are two types of arrays you can use – indexed and associative arrays. Start by declaring the arrays $ declare -a indexed_array $ declare -A associative_array Add values to arrays – note the possibility to add values to arrays with += operator. $ indexed_array[0]=”value1″ $ indexed_array[1]=”value2″ $ indexed_array[2]=”value3″ $ indexed_array+=”value4″ $ indexed_array+=”value5″ $ associative_array[one]=”value1″ […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-866","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.bashpi.org\/index.php?rest_route=\/wp\/v2\/pages\/866","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bashpi.org\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.bashpi.org\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.bashpi.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bashpi.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=866"}],"version-history":[{"count":7,"href":"https:\/\/www.bashpi.org\/index.php?rest_route=\/wp\/v2\/pages\/866\/revisions"}],"predecessor-version":[{"id":1220,"href":"https:\/\/www.bashpi.org\/index.php?rest_route=\/wp\/v2\/pages\/866\/revisions\/1220"}],"wp:attachment":[{"href":"https:\/\/www.bashpi.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=866"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}