Linux Basic — Advanced Scripting

Advanced Scripting

You can now write correct, debuggable scripts. This chapter unlocks the power features — the ones that let a one-line Bash trick replace a 30-line Python helper.

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What You Will Learn

By the end of this chapter you will be able to:

• Stream multi-line input into a command with here-documents (<<EOF)
• Pass a single string as stdin with here-strings (<<<)
• Treat a command’s output as a file with process substitution (<(cmd))
• Isolate scope and side-effects with subshells ( ... ) vs grouping { ... ; }
• Use eval, coproc, and exec deliberately — and know when not to

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Topics in This Chapter

#	Topic	Description
1	Here-Documents	<<EOF and <<-EOF for multi-line input
2	Here-Strings	<<< for single-string stdin
3	Process Substitution	<(cmd) and >(cmd)
4	Subshells & Grouping	( ... ) vs { ... ; }
5	eval, coprocess & exec	dynamic code, two-way pipes, replace shell
6	Practice Exercises	Hands-on tasks

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When Advanced Features Pay Off

These features all solve a recurring problem: how do I plumb data between commands without temporary files or shell loops?

• A heredoc replaces printf "line1\nline2\n..." | cmd
• A here-string replaces echo "$x" | cmd
• Process substitution lets diff, comm, paste compare command outputs directly
• A subshell isolates a cd or set -e change so it doesn’t leak
• exec swaps the script’s stdout to a log file without piping every line

Used together, they keep advanced scripts short, fast, and free of mktemp cleanup boilerplate.

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Next → Here-Documents