- 01Setting up (what you'll need)
- 02Your first shell script (echo)
- 03Using variables
- 04Command-line arguments ($1, $2 ...)
- 05Branching (the if statement)
- 06Repeating (the for loop)
- 07Repeating (the while loop)
- 08Writing your own function
- 09Working with arrays
- 10Command substitution ($())
- 11Working with strings (parameter expansion)
- 12Reading from standard input (read)
- 13Exit status and && / ||
- 14Pipes and redirection
- 15The case statement
- 16Arithmetic ($(( )))
- 17The basics of grep, sed and awk
- 18Argument checks and error handling
- 19Function return values and exit codes
- 20[Project] Build a small log-tallying script
Pipes and redirection
This lesson covers the pipe (|), which hands one command's output to another, and redirection (>), which writes it to a file.
commandA | commandB passes A's output as B's input. command > file writes the output to a file (overwriting it), and >> appends.
The sample code shows the classic use of a pipe: extracting only the lines containing "ERROR" from several lines of log-like text with grep.
A common early stumble is mixing up > (overwrite) and >> (append) and wiping out the contents of an important log file. When you mean to append, always use >>.
In professional work, pipes and redirection are combined daily to pull just the lines you need out of a large log and total them up.
๐งช This site can't compile or run Shell Script directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser โ nothing is sent anywhere).