shell-tricks.md

Shell Command Shortcuts and Tricks Cheat Sheet

History Expansion

• !!: Repeats the last command.
• !$: Last word of the previous command.
• !^: First argument of the previous command.
• !n: Repeats the nth command in your history.
• !-n: Repeats the command n places back in the history list.
• !string: Executes the most recent command starting with 'string'.

Brace Expansion

• {a,b,c}: Expands into a b c (useful for manipulating multiple files).

Tilde Expansion

• ~: Home directory.
• ~username: Home directory of username.

Variable Expansion

• $variable: Value of variable.
• ${variable}: Same as above but useful for appending characters immediately after the variable without ambiguity.

Command Substitution

• $(command): Runs command and uses its output.
• `command`: Older syntax for command substitution.

Arithmetic Expansion

• $((expression)): Evaluates arithmetic expression and substitutes the result.

Wildcard Expansion (Globbing)

• *: Matches any characters.
• ?: Matches any single character.
• [abc]: Matches any one character listed.

Quoting

• " ": Double quotes (special characters except $, \, and backticks lose special meaning).
• ' ': Single quotes (everything is taken literally).

Redirection and Pipes

• >: Redirects output to a file, overwriting existing contents.
• >>: Appends the output to the end of a file.
• <: Takes input from a file.
• |: Directs output of one command to another.