Shell

• Search all the man pages for a keyword
  • man -k searchTerm
    • e.g.
      • man -k directory
        • views all of the man pages related to the command directory such as mkdir, ls, etc.
• man man
• man intro
  • good intro guide to the command line
• man bash
• From Inside the man page
  • /searchTerm
    • searches inside that man page
    • n
      • goes to the next found term

• description of what the command does

• Lists all available commads

• shows the path to that command - where the actual binary is located as determined by $PATH environment variable
• which python3
• which ls

• <> are often used in Syntax guides to indicate that the <> surround a place for a command rather than an actual command. | is used to denote OR or Optional so in the line above we read that a Command can be used on its own but may be followed by Switches (single letters, preceded by a hyphen that adjust what the command does), Parameters (Things that the command needs to know in order to work) and a Target (The thing that the command will be applied to).
• switches aka options aka flags
  • often work either shorthand with one dash -U or with a full name -user
  • Evaluate to Boolean
  • Shorthand -a
  • Longhand --all

• Autocomplete partially typed commands, files, etc.
• If there are multiple possibilities, tab won’t complete, but if you double tap tab you’ll get a list of the possibilities
  • Good for finding the names of options and switches
  • Good for finding all the apps that start with a set of letters with apt-get install for example

• Cycles through previous inputs

• Halts the current command, cancel the current operation and/or start with a fresh new line - sends a sigint

• quits a terminal mode, like in less, e.g. - Ctrl-c doesn’t work in less. I think it might be in vi or something

• Stops the current command, resume with fg in the foreground or bg in the background

• Recent commands
• Can search them as well?

• Clears the screen leaving your typing there
• Equivalent to the clear BASH command

• Exits the shell

• REISUB

• Cursor to start of line

• Cursor to end of line

• Cut/Delete left of cursor

• Cut/Delete right of cursor

• Cut/Delete word to left of cursor

• Paste what you cut via Ctrl-U or K or W

• E.g. If you forget sudo you could just type "sudo !!"

• E.g.
  • Mkdir ~/docs/Evan
  • Cd !$

• e.g.
  • sudo apt-get upgrade &
  • ping google.com & ping apple.com &
    • runs both commands in background

• cycles through previous terminal commands

• command to list your terminal history
• !num
  • !53
  • executes specific numbered command
• !num:p
  • To edit a command from history
  • This prints the comnand instead of executing it so that you can then arrow up to edit it
• history with datestamps
  • $ HISTTIMEFORMAT="%F %T " $ history
  • This is only valid for the current session, but you can also add this to your bash profile if you want that to be permanent
• sudo !! trick to repeat last command with sudo prepended
  • omnioutliner:///open?row=dOpCUN901UY

• usually per line?
• a pun on more
• q to quit
• I think it runs in vi

• usually per page?

• function hello { echo Hello! } $ hello

• STR="Hello World!" echo $STR

• unset variable_name

• ""
• ''

• cat bands.txt | wc
• cat bands.txt | sort | grep The*

• "The xargs command in UNIX is a command line utility for building an execution pipeline from standard input. Whilst tools like grep can accept standard input as a parameter, many other tools cannot. Using xargs allows tools like echo and rm and mkdir to accept standard input as arguments."
• execute arguments
• echo 'one two three' | xargs mkdir ls one two three
  • "By default xargs reads items from standard input as separated by blanks and executes a command once for each argument. In the following example standard input is piped to xargs and the mkdir command is run for each argument, creating three folders."

• Instead of output going to screen it goes to a file
• e.g.
  • ls -l Documents > documents.txt
  • sort < bands.txt
  • sort < bands.txt > bands_sorted.txt

makes the output appended to the file instead of overwriting

• goes the other way
• redirects stdin instead of stdout?
• e.g.
  • cat gymnastics.txt is the same as cat < gymnastics.txt

• commands are interpreted in order

• if
• then
• else
• fi
• e.g.
  • if ls *.txt ; then echo We’ve found text files ; else echo No files found ; fi

• touch file; sleep 10; rm file <-- 10 seconds

• Collection Traversal
  • seq method is outdated
    • for i in `seq 1 10`; do echo $i done
  • for i in $( ls ); do echo item: $i done
  • for i in {1...3} do echo $i done

• Example
  • count=0 while [ $count -lt 100 ]; do echo $count let count=count+1 done

• Like while loop but in reverse, basically. But I think you can just use boolean ! to get the same thing?
• Example
  • COUNTER=20 until [ $COUNTER -lt 10 ]; do echo COUNTER $COUNTER let COUNTER-=1 done

• C, C++, Java like syntax #issue
  • start=4
  • end=12
  • jump=4
  • for (( i = $start ; i <= $end ; i += $jump ))
  • do
  • echo $i
  • done

• HUP
• INT
• QUIT
• ILL
• TRAP
• ABRT
• EMT
• FPE
• KILL
• BUS
• SEGV
• SYS
• PIPE
• ALRM
• TERM
• URG
• STOP
• TSTP
• CONT
• CHLD
• TTIN
• TTOU
• IO
• XCPU
• XFSZ
• VTALRM
• PROF
• WINCH
• INFO
• USR1
• USR2
• The basic Linux signals all have a number (1-30+)
• A number of signals can be captured and redirected by the process, whereas others cannot - e.g. 9/kill
• SIGTERM
  • 15
  • may be ignored
• SIGKILL
  • 9
  • forces termination
  • only use if needed - if hanging
• SIGINT

• e.g.
  • rm -r !(*.txt)
    • delete all files except for txt files

• The $(...) shell operator executes the command within parentheses and substitutes its output into the command line.
• e.g.:
  • docker rm -vf $(docker ps -a -q)

• calculator

• Normally quotes are unnecessary

• Allows you to use special characters
• e.g.
  • echo “First line/nSecond Line/nThird Line”

• cat file1 file2 > file3
  • concatenates file1 and file2 together in file3
• cat file1 | less
  • displays contents of file1 on screen and pauses before each screen advance
• cat file1 file2 file 3 | sort > file 4
  • concatenates file1, file2, and file3, pipes it to the sort filter which alphabetizes each line before it is written to file4

• Wraps the lines of myfile.txt to a width of 5 characters, and writes the output to newfile.txt.

• I think needs a Bash upgrade on macOS
• [31m controls the text color
• 30-37 sets foreground color
• 40-47 sets background color
• -e allows escaped characters

• tests the default audio device by playing tones

• plays a sound file

• text to speech?

• Can make gifs e.g.

• (Plays all wav files it can find)

• Does a file named name exist in the working directory

• is the fike named name a directory?