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cheat_sheets/linux/linux_metacharacters.md
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cheat_sheets/linux/linux_metacharacters.md
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# Linux metacharacters
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1. `;` : Separates commands.
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```
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command1 ; command2 # Run command1, then run command2 regardless of whether command1 succeeded.
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```
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2. `&` : Background execution.
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```
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command & # Runs "command" in the background.
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```
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3. `&&` : AND operator.
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```
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command1 && command2 # Run command1, then run command2 only if command1 succeeded.
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```
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4. `||` : OR operator.
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```
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command1 || command2 # Run command1, then run command2 only if command1 failed.
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```
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5. `|` : Pipe operator.
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```
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command1 | command2 # Output of command1 is passed as input to command2.
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```
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6. `()` : Command group.
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```
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(command1; command2) # Group commands into a subshell.
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```
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7. `{}` : Command block.
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```
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{ command1; command2; } # Group commands in the current shell.
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```
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8. `$()` : Command substitution.
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```
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echo $(command) # Runs "command" and substitutes its output in place.
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```
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9. ` `` ` (Backticks): Another way of command substitution.
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```
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echo `command` # Same as above, but this syntax can be harder to spot.
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```
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10. `>` : Output redirection.
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```
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command > file # Redirect the output of command to a file, overwriting the file.
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```
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11. `>>` : Append output.
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```
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command >> file # Append the output of command to a file.
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```
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12. `<` : Input redirection.
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```
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command < file # Use "file" as input for command.
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```
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13. `2>` : Error redirection.
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```
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command 2> file # Redirect the error output of command to a file, overwriting the file.
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```
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14. `2>>` : Append error output.
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```
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command 2>> file # Append the error output of command to a file.
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```
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15. `&>` : Redirect all output (stdout and stderr).
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```
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command &> file # Redirect all output of command to a file, overwriting the file.
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```
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16. `*` : Wildcard.
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```
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ls *.txt # List all .txt files.
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```
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17. `?` : Single character wildcard.
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```
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ls ?.txt # List all .txt files with a single character name.
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```
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18. `[]` : Character class.
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```
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ls [ab]*.txt # List all .txt files starting with 'a' or 'b'.
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```
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19. `!` : Negation.
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```
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command1; ! command1 # Execute command1, then execute command1 again only if the first execution failed.
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```
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20. `#` : Comment.
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```
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# This is a comment in Bash.
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```
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21. `\$` : Escape character.
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```
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echo \$HOME # prints $HOME, not the value of the variable.
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```
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22. `\"` : Escape character for quotes.
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```
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echo "This is a \"quote\"" # prints This is a "quote".
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```
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Be careful, especially when using redirections, as they can overwrite your files without warning if you're not careful.
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