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Useful tricks for running commands

Useful tricks for running commands#

As commands can become quite complex in their structure when adding multiple options(s) and argument(s) and any typing error will lead a failed command, it is important to make your commands as reproducible as possible. One way to achieve this is by using tricks for running commands that make the typing more efficient, prevent mistakes and allow tracking of commands that you ran previously to ensure you can re-run them. And importantly, it saves a lot of time.

  • You can use the ‘Up’ and ‘Down’ arrow keys to navigate through previously used commands (known as your history) and repeat or modify them.

  • When typing a command or file name, you can press the ‘Tab’ key to auto complete what you are typing. If there are multiple commands or files with similar names, auto completion will fill in as far as the first ambiguous character before you have to give it some more input. This method makes it much less likely that you make a spelling error. Also, if you double press the ‘tab’ key all the available options to complete will be shown.

  • Windows: To copy text from the terminal you will have to ‘Highlight’ -> ‘Right-click’ -> ‘Copy’. Similarly you have to use the in-browser menu ‘Right-click’ -> ‘Paste’ to paste your selected text into the terminal. The reason for this is that Ctrl + c and Ctrl + v have effects inside the terminal.

  • Mac: You can fortunately use ‘Cmd + c’ and ‘Cmd + v’ to copy and paste as normal. You can use Ctrl and various keys for in-terminal commands.

  • Pressing ‘Ctrl + l’ will clear the screen.

  • Pressing ‘Ctrl + r’ will allow you to search through your command history.

  • See previous commands by typing history and pressing enter.

  • Pressing ‘Ctrl + c’ will send an interrupt signal that cancels the currently running command and brings you back to the command line.

  • ‘Double-click’ to select a word, ‘Triple-click’ to select a line

  • Using a ‘#’ character as part of a command allows you to make comments that have no effect when run.

Exercise 1.2#

Exercise 1.2

  • Use the arrow key to execute the same command again

 # Press the up arrow once and the last command appears
echo 'My first command'

  • Try typing e then pressing tab twice, what do you see?

# You see all the possible commands that start with "e" when you press tab twice after entering “e”
e2freefrag             edquota                era_check              eu-readelf
e2fsck                 efibootdump            era_dump               eu-size
e2image                efibootmgr             era_invalidate         eu-stack
e2label                efikeygen              era_restore            eu-strings
e2mmpstatus            efisiglist             esac                   eu-strip
e2undo                 efivar                 escputil               eutp
e4crypt                egrep                  espdiff                eu-unstrip
e4defrag               eject                  espeak-ng              eval
eapol_test             elfedit                ether-wake             evince
easy_install-2         elif                   ethtool                evince-previewer
easy_install-2.7       else                   eu-addr2line           evince-imageer
easy_install-3         enable                 eu-ar                  evmctl
easy_install-3.6       encguess               eu-elfclassify         ex
ebtables               enchant-2              eu-elfcmp              exec
ebtables-restore       enchant-lsmod-2        eu-elfcompress         exempi
ebtables-save          enscript               eu-elflint             exit
echo                   env                    eu-findtextrel         exiv2
ed                     envsubst               eu-make-debug-archive  expand
edgepaint              eog                    eu-nm                  export
edid-decode            eps2eps                eu-objdump             exportfs
editdiff               eqn                    eu-ranlib              expr

  • Try adding c to make ec and pressing tab again. What happens?

# The command autocompletes after adding the “c” to the “e”
echo

  • Try to copy/paste your echo command “echo ‘My first command’”

# Note that ctrl + c to copy does not work in windows terminal or mobaxterm - instead highlighting text automatically copies it
# In mobaxterm ctrl + v to paste also does not work - instead right-click to paste
echo 'My first command'

  • Try to clear the screen, can you still paste your echo command?

# To clear the screen use ctrl + l or the command 'clear' and you can still paste the command
echo 'My first command'

  • Try to using your command history with ctrl+r, to re-run your last command. How many letters of echo do you need to type to find your previous command?

# To search through your command history, type ctrl + r, typing e is sufficient to find your last command, press enter to re-run the command

  • Press ctrl + r again, then imagine you wanted to search by history instead of ctrl+r, thus try to interrupt your command. What happens?

# After typing ctrl + r, type ctrl + c to interrupt that command, then type history and you can copy/paste your command from the history to re-run
# Then either double-click on each word in your command and copy/paste or instead triple-click on the line of words to copy/paste and then remove the line number to re-run the command

  • What will happen to your command history when you log out of the server and re-connect?

# Check your history
history

# Exit from the server and close the window
exit

# Re-connect to the server and check your history
ssh <your eth username>@cousteau.ethz.ch
history

  • Run your first command with a comment describing what this command does. What happens to the comment?

# Run your first command with a comment describing what it does after #
echo 'My first command' #This command prints 'My first command' on the command line
# Notice that your comment after the # is not displayed in your result
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