- 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 ($(( )))
- 17The basics of grep, sed and awk
- 18Argument checks and error handling
- 19Function return values and exit codes
- 20[Project] Build a small log-tallying script
Command substitution ($())
This lesson covers command substitution, which captures the output of a command into a variable.
Writing $(command) takes the output of the command as a string, which you can then assign to a variable or pass to another command.
The sample code writes today=$(date +%Y-%m-%d) to fetch today's date into a variable and embeds it in a message.
A common early stumble is the difference from the older backtick form, `command`. Both mean the same thing, but $() nests more easily and reads better, so it is the recommended form today.
In professional work, command substitution comes up constantly for branching on the result of a command and for putting a timestamp into a log file name.
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).