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One of the most important features of Bash is to handle large strings. Here is an example of how you can use multi-line strings in Bash to represent documents:
document=$(cat <<EOF
This is a multi-line string
representing a document.
You can have as many lines
as you want.
EOF
)
echo "$document"
# This will print:
This is a multi-line string
representing a document.
You can have as many lines
as you want.
We use the <<EOF notation to indicate the start of a multi-line string, and EOF to indicate the end. Anything between these markers will be treated as part of the string.
We assign the result to a variable named document in this case. Then we echo the variable to print the entire multi-line string.
Multi-line strings are useful when you want to represent longer texts, documents or configuration files in your Bash scripts. The text within the string can contain new lines, spaces and tabs, and Bash will preserve the formatting.
String Interpolation
Here is how you can use string interpolation to insert variables into large strings in Bash:
name="John"
age=30
document=$(cat <<EOF
Hello, my name is $name and I am $age years old.
I enjoy programming in Bash.
EOF
)
echo "$document"
# This will print:
Hello, my name is John and I am 30 years old.
I enjoy programming in Bash.
We define two variables - name and age.
Then we use the <<EOF notation to define a multi-line string, representing a document. Within that string, we use $name and $age to insert the variable values.
This is called string interpolation - inserting variable values into a string. We assign the result to the document variable and then echo it to print the full text with the variable values inserted.
The output will be:
Hello, my name is John and I am 30 years old.
I enjoy programming in Bash.
So by combining multi-line strings and string interpolation, we can construct longer documents programmatically in Bash, inserting variable data into the text.
Use-Cases
Here are some use cases of multi-line strings in Bash:
Representing longer texts or documents: As we saw in the previous examples, multi-line strings are useful when you want to represent longer texts, configurations or documents within your Bash scripts.
Template strings: You can use multi-line strings as templates, and then insert variable data into them using string interpolation. This is useful for generating customized output.
Here documents: Multi-line strings are also used with here documents, which redirect the output of the string to a command's standard input. This is used to pass longer inputs to commands.
Configuration files: You can construct configuration files programmatically using multi-line strings and string interpolation. This allows you to generate customized config files from within your scripts.
SQL queries: Multi-line strings are useful for representing longer SQL queries within Bash scripts. You can insert table names, column names and other variables into the SQL string.
Email messages: Similarly, you can generate customized email messages from within Bash scripts using multi-line strings and string interpolation.
Logging: Multi-line strings allow you to construct more descriptive log messages within your Bash scripts, including variable data and details.
So in summary, any time you want to represent longer texts, templates or documents within Bash, or generate customized output programmatically, multi-line strings become very useful.
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