Shell Scripting & Piping
The problem
Running the same sequence of commands repeatedly by hand is slow and error-prone — shell scripting lets you save a sequence of commands as a reusable program, and piping lets you compose small, single-purpose commands into a larger pipeline without writing new code for each combination.
Why now
Interprocess communication already described the pipe as an OS mechanism connecting two processes' input and output; piping in the shell is that exact mechanism exposed as a one-character syntax (|). Control flow already gave branching and looping in general — shell scripts are just that same vocabulary applied to sequences of commands instead of function calls.
Mental model
A pipeline is an assembly line: each command's standard output becomes the next command's standard input, letting you compose tiny, focused tools (grep, sort, wc) into something none of them could do alone. A shell script is just a saved, repeatable pipeline plus the same branch/repeat control flow you already know, applied to commands instead of function calls.
Requires
- Interprocess CommunicationOperating Systems
Piping (|) is literally the pipe IPC mechanism, invoked with one character between two commands instead of two lines of code; the underlying data-flow guarantee is identical.
- Control FlowProgramming Fundamentals
Shell scripts use the same branch (if) and repeat (for, while) primitives as any programming language; you need that vocabulary to read or write anything beyond a single command.
Unlocks
Used in
- Build and deployment automation scripts
- Log analysis pipelines (grep | sort | uniq -c to summarize error frequency)
- CI/CD pipeline steps, which are almost entirely shell scripts under the hood
- Cron jobs — scheduled shell scripts running maintenance or reporting tasks
Projects
- Write a shell script that finds all files matching a pattern, counts lines in each, and reports the total — combining find, wc, and a loop
- Build a pipeline (using grep, sort, uniq -c) that summarizes the most frequent error messages in a log file
Examples
- cat access.log | grep '500' | wc -l counts server errors by chaining three single-purpose tools
- A deploy script wraps a sequence of build, test, and upload commands into one repeatable, version-controlled file
Resources
Mastery checklist
- I can chain at least three commands together with pipes to solve a real text-processing task
- I can write a shell script using variables, a conditional, and a loop
- I can explain what standard input, output, and error are and how piping connects them
- I can make a script executable and run it directly