Shell Reference

Basics

`.`	a single period refers to the current directory
`..`	a double period refers to the directory immediately above the current directory
`~`	refers to your home directory. Note: this command does NOT work on Windows machines (Mac and Linux are okay)
`cd ./dirname`	changes the current directory to the directory `dirname`
`ls -F`	tells you what files and directories are in the current directory
`pwd`	tells you what directory you are in (`pwd` stands for print working directory)
`history`	lists previous commands you have entered. `history \| less` lets you page through the list.
`man` cmd	displays the manual page for a command.

`mkdir ./dirname`	makes a new directory called dirname below the current directory. Note: Windows users will need to use `\` instead of `/` for the path separator
`rm ./filename`	deletes a file called `filename` from the current directory
`rmdir ./dirname`	deletes the directory `dirname` from the current directory. Note: `dirname` must be empty for `rmdir` to run.
`mv tmp/filename .`	moves the file `filename` from the directory `tmp` to the current directory. Note: (i) the original `filename` in `tmp` is deleted. (ii) `mv` can also be used to rename files (e.g., `mv filename newname`
`cp tmp/filename .`	copies the file `filename` from the directory `tmp` to the current directory. Note: (i) the original file is still there

`*`	zero or more characters
`?`	exactly one character
`[abcde]`	exactly one of the characters listed
`[a-e]`	exactly one character in the given range
`[!abcde]`	any character not listed
`[!a-e]`	any character that is not in the given range
`{software,carpentry}`	exactly one entire word from the options given

`>`	write `stdout` to a new file; overwrites any file with that name (e.g., `ls *.md > mardkownfiles.txt`)
`>>`	append `stdout` to a previously existing file; if the file does not exist, it is created (e.g., `ls *.md >> markdownfiles.txt`)
`<`	assigns the information in a file to a variable, loop, etc (e.g., `n < markdownfiles.md`)
\|	Output from one command line program can be used as input to another one (e.g. ls .md \| head gives you the first 5 `.md` files in your directory)

`grep [options] day haiku.txt`	finds every instance of the string `day` in the file haiku.txt and pipes it to standard output
`-E`	tells grep you will be using a regular expression. Enclose the regular expression in quotes.
`-i`	makes matching case-insensitive
`-n`	limits the number of lines that match to the first n matches
`-v`	shows lines that do not match the pattern (inverts the match)
`-w`	outputs instances where the pattern is a whole word

`find start [options] [commands]`	look for files or directories with specified properties and take specified actions
`-type d`	match directories
`-type f`	match files
`-name 'pattern'`	match things with specific names
`-maxdepth n`	maximum search depth
`-mindepth n`	minimum search depth
`-print`	print matches

for filename in *.txt
do
    head -5 $(filename) | sort | uniq -c
done

history | tail -20 > recent-commands.sh