bash

https://changelog.com/posts/bash-it-a-community-bash-framework

http://fahdshariff.blogspot.com/2017/05/shell-scripting-and.html

< allows you to pass data contained in a file to the standard input of a command. The format is:

command < file

Examples:

# replace comma with new-lines: tr ',' '\n' < file   # read a file line-by-line and do something with each line: while IFS= read -r line; do   # do something with each line   ssh "$line" who -b done < hosts.txt

2. <<
<< allows you to pass multi-line text (called a here-document) to a command until a specific "token" word is reached. The format is:

command << TOKEN line 1 line 2 TOKEN

For example:

# query a database sqsh -S server -D db << END select * from table where foo='bar' go END

3. <<<
<<< allows you to pass a string of text (called a here-string) to a command. If you find yourself echo-ing text and piping it to a command, you should use a here-string instead. (See my previous post on Useless Use of Echo.) The format is:

command <<< text

Examples:

tr ',' '\n' <<< "foo,bar,baz"   grep "foo" <<< "foo,bar,baz"   mailx -s subject $USER <<< "email body"