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Set shell variable

2016-09-08T10:00:00-06:00

To see what a shell variable is currently set to you can echo it.

$ echo "$RAILS_ENV"

To set a shell variable you export it.

$ export RAILS_ENV=production

2016-09-07T10:00:00-06:00

Structure of a find command:

find where-to-look criteria action

$ find . -name "*front*" -print
#=> print out files that contain "front" in the current directory

$ find / -name foo.txt
#=> find a file called foo.txt from root

To avoid permission denied use the following:

$ find . ! -readable -prune -o -name '*.txt'
#=> find all readable .txt files from current directory

2016-05-15T10:00:00-06:00

$ cp source dest

Some of the options for copying things.

Command
cp -a	Preserves structure and attributes of file but not directory structure, ie permissions, etc.
cp -i	Interactive mode
cp -R	If source file is a directory copy the directory and entire subtree - If the source file end in / copies the contents of the directory
cp -v	Verbose mode
cp -n	Do not overwrite an existing file

2016-04-12T10:00:00-06:00

2016-04-07T10:00:00-06:00

$ set -o

2016-04-07T10:00:00-06:00

Command	Action	Example usage
>	Redirect standard output	Write to file
>!	Redirect standard output; overwrite file if it exists
>&	Redirect standard output and standard error
<	Redirect standard input	Read from file
\|	Redirect standard output to another command (pipe)
>>	Append standard output	Append to file

2016-04-06T10:00:00-06:00

Prepend time to a command to see how long it takes to run.

Example:

$ time sleep 12

2016-04-06T10:00:00-06:00

Some of the options for removing things.

Command
rm -d	Attempt to remove directories as well as other types of files.
rm -f	Attempt to remove file without prompting for confirmation. If file does not exist, do not display diagnostic message. The `-f` option overrides any previous `-i` options.
rm -i	Interactive mode
rm -R	Attempt to remove the file hierarchy rooted in each file argument. The `-R` option implies the `-d` option.
rm -v	Verbose mode

2016-04-06T10:00:00-06:00

Some of the options for listing things.

Command
ls -F	Display directorys with a trailing / - an asterisk after each executable, etc
ls -l	List in long format
ls -lh	Long list with human readible sizes
ls -t	Sort by time modified
ls -S	Sort by size
ls -r	Reverse the order of sorting
ls -R	Recursively list subdirectories encountered

2016-04-06T10:00:00-06:00

Some of the options for the du command.

Command
du -a	Display an entry for each file in a file hierarchy
du -s	Display an entry for each specified file
du -c	Display a grand total
du -h	Human readable